Article pubs.acs.org/IC

Uranyl Ion Complexes with Long-Chain Aliphatic α,ω-Dicarboxylates and 3d-Block Metal Counterions Pierre Thuéry*,† and Jack Harrowfield‡ †

NIMBE, CEA, CNRS, Université Paris-Saclay, CEA Saclay, 91191 Gif-sur-Yvette, France ISIS, Université de Strasbourg, 8 allée Gaspard Monge, 67083 Strasbourg, France

‡

S Supporting Information *

ABSTRACT: Twelve new complexes were obtained from reaction of uranyl ions with the aliphatic dicarboxylic acids HOOC−(CH2)n−2−COOH (H2Cn; n = 7−10 and 12) under solvo-hydrothermal conditions, in the presence of 3d-block metal ions (Mn2+, Fe3+, Co2+, Ni2+, and Cu2+) and 2,2′-bipyridine (bipy) or 1,10-phenanthroline (phen). In contrast to previously reported triple-stranded helicates obtained with C92− and C122−, all these complexes crystallize as polymeric one-dimensional (1D) or two-dimensional (2D) species. [Fe(bipy)3][(UO2)2(C7)3]·3H2O (1), [Cu(phen)2]2[(UO2)3(C7)4(H2O)2]·2H2O (2), and [Cu(bipy)2]2[(UO2)2(C9)3] (6), in which the 3d cation was reduced in situ, are 1D ladderlike polymers displaying tetra- or hexanuclear rings, of sufficient width to encompass two counterions in 2 and 6. The three complexes [Co(phen)3][(UO2)3(C8)3(O)]·H2O (3), [Ni(phen)3][(UO2)3(C8)3(O)]·H2O (4) and [Co(phen)3][(UO2)3(C9)3(O)]·H2O (5) contain bis(μ3-oxo)-bridged tetranuclear secondary building units, and they crystallize as deeply furrowed 2D assemblies. Depending on the nature of the counterion, C102− gives [Ni(bipy)3][(UO2)2(C10)3]·2H2O (7), a 2D network displaying elongated decanuclear rings containing the counterions, or [Mn(phen)3][(UO2)2(C10)3]·6H2O (8), [Co(phen)3][(UO2)2(C10)3]·7H2O (9), and [Ni(phen)3][(UO2)2(C10)3]·7H2O (10), which consist of 2D assemblies with honeycomb topology; the hexanuclear rings in 8−10 are chairlike and occupied by one counterion and two uranyl groups from neighboring layers. Two complexes of the ligand with the longest chain, C122−, are reported. [UO2(C12)(bipy)] (11) is a neutral 1D species in which bipy chelates the uranyl ion and plays an important role in the packing through π-stacking interactions. Two polymeric units, 1D and 2D, coexist in the complex [Ni(bipy)3][(UO2)2(C12)3][UO2(C12)(H2O)2]·H2O (12); the 2D network has the honeycomb topology, but the hexanuclear rings are markedly convoluted, with local features akin to those in helicates, and the counterions are embedded in intralayer cavities. Emission spectra measured in the solid state show in most cases various degrees of quenching, with intense and well-resolved uranyl emission being observed only for complexes 2 and 11.

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INTRODUCTION Considering the wealth of diverse and often original architectures that have been observed in uranyl−organic coordination polymers and frameworks with virtually all common poly(carboxylic acid)s,1 the search for novel topologies now depends largely on modifications of the synthetic procedures, such as solvent, concentration or temperature changes, or addition of coligands or other metallic species. The use of different organic solvents in solvo-hydrothermal synthesis has proved a worthwhile approach,2 while addition of alkali, alkaline-earth, d-, p-, or f-block metal cations has been much investigated and is often a path to dimensionality increase.3 We have recently been particularly interested in the use of [M(bipy/phen)3]2+ counterions (where M = 3d-block metal cation, bipy = 2,2′-bipyridine, and phen = 1,10phenanthroline) as structure-directing species, as illustrated by the synthesis of original polycatenated systems incorporating such cations and the 4,4′-biphenyldicarboxylate ligand.4 Other elongated dicarboxylic acids suitable for a similar study are the linear aliphatic α,ω-diacids of general formula HOOC− (CH2)n−2−COOH (H2Cn), and it is notable that triple © XXXX American Chemical Society

interpenetration has previously been found in the mixed ligand complex [UO2(C6)(4,4′-bipy)].5 Examples of uranyl complexes with the acids corresponding to n = 4 (succinic)6 and 5 (glutaric)6c,7 are well-known (acids with n < 4 will be disregarded here), and those with the longer molecules, n = 6 (adipic), 7 (pimelic), 8 (suberic), 9 (azelaic), and 10 (sebacic) have been investigated in great detail by Cahill’s group.5,8 The association of these latter ligands with molecules in the bridging bipyridine family, 4,4′-bipyridine, 1,2-bis(4-pyridyl)ethane, and trans-1,2-bis(4-pyridyl)ethylene, was particularly studied, and the various roles assumed by these molecules (uranyl coordination, charge balance, and structure-direction) have been shown to be related to the length matching with the dicarboxylate ligand.5,8c Combination of these long-chain dicarboxylates (n = 7−10) with the more exotic cucurbiturils has also been explored, the latter macrocycles proving to be either coordinated or enclosed within the lattice.9 It is notable that although many uranyl complexes with the Cn2− anions Received: November 4, 2015

A

DOI: 10.1021/acs.inorgchem.5b02540 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry

autogenous pressure, giving light yellow crystals of complex 3 within 10 d (5 mg, 11% yield based on U). Anal. Calcd for C60H62CoN6O20U3: C, 36.77; H, 3.19; N, 4.29. Found: C, 36.90; H, 3.10; N, 4.34%. In one experiment, 3 was obtained alongside a larger quantity of the previously reported complex [UO2Co(C8)2(phen)2]2, the latter having been obtained pure in another similar experiment.10 [Ni(phen)3][(UO2)3(C8)3(O)]·H2O (4). Suberic acid (H2C8, 18 mg, 0.10 mmol), UO2(NO3)2·6H2O (33 mg, 0.07 mmol), Ni(NO3)2· 6H2O (10 mg, 0.03 mmol), 1,10-phenanthroline (18 mg, 0.10 mmol), DMF (0.25 mL), and demineralized water (0.5 mL) were placed in a 10 mL tightly closed glass vessel and heated at 140 °C under autogenous pressure, giving light yellow crystals of complex 4 within three weeks. The solution was filtered while hot, and the crystals were washed with hot water (23 mg, 50% yield based on U). Anal. Calcd for C60H62N6NiO20U3: C, 36.77; H, 3.19; N, 4.29. Found: C, 37.19; H, 3.09; N, 4.36%. [Co(phen)3][(UO2)3(C9)3(O)]·H2O (5). Azelaic acid (H2C9, 19 mg, 0.10 mmol), UO2(NO3)2·6H2O (33 mg, 0.07 mmol), Co(NO3)2· 6H2O (10 mg, 0.03 mmol), 1,10-phenanthroline (18 mg, 0.10 mmol), DMF (0.25 mL), and demineralized water (0.5 mL) were placed in a 10 mL tightly closed glass vessel and heated at 140 °C under autogenous pressure, giving light yellow crystals of complex 5 within one week. The solution was filtered while hot, and the crystals were washed with hot water (11 mg, 24% yield based on U). Anal. Calcd for C63H68CoN6O20U3: C, 37.79; H, 3.42; N, 4.20. Found: C, 37.96; H, 3.32; N, 4.17%. [Cu(bipy)2]2[(UO2)2(C9)3] (6). Azelaic acid (H2C9, 19 mg, 0.10 mmol), UO2(NO3)2·6H2O (33 mg, 0.07 mmol), Cu(NO3)2·2.5H2O (7 mg, 0.03 mmol), 2,2′-bipyridine (16 mg, 0.10 mmol), DMF (0.25 mL), and demineralized water (0.5 mL) were placed in a 10 mL tightly closed glass vessel and heated at 140 °C under autogenous pressure, giving dark orange crystals of complex 6 in low yield within one week. [Ni(bipy)3][(UO2)2(C10)3]·2H2O (7). Sebacic acid (H2C10, 20 mg, 0.10 mmol), UO2(NO3)2·6H2O (33 mg, 0.07 mmol), Ni(NO3)2· 6H2O (10 mg, 0.03 mmol), 2,2′-bipyridine (16 mg, 0.10 mmol), DMF (0.25 mL), and demineralized water (0.5 mL) were placed in a 10 mL tightly closed glass vessel and heated at 140 °C under autogenous pressure, giving light orange-pink crystals of complex 7 overnight. The solution was filtered while hot, and the crystals were washed with hot water (8 mg, 13% yield). Anal. Calcd for C60H76N6NiO18U2: C, 42.29; H, 4.50; N, 4.93. Found: C, 41.50; H, 4.36; N, 4.71%. [Mn(phen)3][(UO2)2(C10)3]·6H2O (8). Sebacic acid (H2C10, 20 mg, 0.10 mmol), UO2(NO3)2·6H2O (33 mg, 0.07 mmol), Mn(NO3)2· 4H2O (8 mg, 0.03 mmol), 1,10-phenanthroline (18 mg, 0.10 mmol), DMF (0.25 mL), and demineralized water (0.5 mL) were placed in a 10 mL tightly closed glass vessel and heated at 140 °C under autogenous pressure, giving light yellow crystals of complex 8 within one month. The solution was filtered while hot and the crystals were washed with hot water (30 mg, 46% yield). The presence of approximately two water molecules in excess of the number found from crystal structure determination is indicated by elemental analysis. Anal. Calcd for C66H84MnN6O22U2 + 2H2O: C, 42.16; H, 4.72; N, 4.47. Found: C, 41.94; H, 4.34; N, 4.43%. [Co(phen)3][(UO2)2(C10)3]·7H2O (9). Sebacic acid (H2C10, 20 mg, 0.10 mmol), UO2(NO3)2·6H2O (33 mg, 0.07 mmol), Co(NO3)2· 6H2O (10 mg, 0.03 mmol), 1,10-phenanthroline (18 mg, 0.10 mmol), DMF (0.25 mL), and demineralized water (0.5 mL) were placed in a 10 mL tightly closed glass vessel and heated at 140 °C under autogenous pressure, giving light orange crystals of complex 9 overnight. The solution was filtered while hot, and the crystals were washed with hot water (32 mg, 49% yield). Anal. Calcd for C66H86CoN6O23U2: C, 42.47; H, 4.64; N, 4.50. Found: C, 42.39; H, 4.35; N, 4.51%. [Ni(phen)3][(UO2)2(C10)3]·7H2O (10). Sebacic acid (H2C10, 20 mg, 0.10 mmol), UO2(NO3)2·6H2O (33 mg, 0.07 mmol), Ni(NO3)2· 6H2O (10 mg, 0.03 mmol), 1,10-phenanthroline (18 mg, 0.10 mmol), DMF (0.25 mL), and demineralized water (0.5 mL) were placed in a 10 mL tightly closed glass vessel and heated at 140 °C under autogenous pressure, giving light pink crystals of complex 10 overnight. The solution was filtered while hot, and the crystals were

crystallize as one-dimensional (1D) or two-dimensional (2D) species, molecular complexes6e,9a and three-dimensional (3D) frameworks6a,c,8a,c,9b have also been observed. In a recent work on uranyl complexes synthesized under solvo-hydrothermal (water/N,N-dimethylformamide (DMF)) conditions with H2C8, H2C9, and dodecanedioic acid (H2C12), using [M(bipy/phen)3]2+ counterions (M = Mn, Co, Ni), we obtained the anionic triple-stranded helicates [(UO2)2(C9)3]2− and [(UO2)2(C12)3]2−, the first ever reported in uranyl chemistry, as well as the neutral metallacycles [UO2M(C8)2(phen)2]2 (M = Mn, Co).10 In the former case, the uranyl ion is chelated by three carboxylate groups from three Cn2− ligands, these being sufficiently flexible to allow the formation of a closed binuclear species with both uranyl ions on a threefold rotation axis. The value n = 9 seems to be the lowest possible for such an arrangement, and a dinuclear uranyl complex with only two dicarboxylate spacers and pendent M(phen)2 groups was obtained for n = 8. In the course of this work, several 1D and 2D assemblies were also synthesized with acids H2C7− H2C10 and H2C12, in the presence of 3d-block metal cations and either bipy or phen, that have now been characterized by their crystal structure and their emission spectrum in the solid state, as described herein. The uranyl complexes with H2C12 reported here and in our previous work are the first with this diacid, for which only a handful of metal complexes are known,11 while no metal complex with a higher member in the H2Cn family is reported in the Cambridge Structural Database (CSD, Version 5.35).12

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EXPERIMENTAL SECTION

Syntheses. Caution! Uranium is a radioactive and chemically toxic element, and uranium-containing samples must be handled with suitable care and protection. UO2(NO3)2·6H2O (depleted uranium, R. P. Normapur, 99%), Co(NO3)2·6H2O, and Ni(NO3)2·6H2O were purchased from Prolabo, Mn(NO3)2·4H2O was from Merck, 2,2′-bipyridine (bipy) was from Fluka, and NH4Fe(SO4)2·12H2O, Cu(NO3)2·2.5H2O, the carboxylic acids, and 1,10-phenanthroline (phen) from Aldrich. Elemental analyses were performed by MEDAC Ltd. at Chobham, U.K. Infrared spectra, recorded on the pure solids on a Nicolet 6700 FTIR instrument using a diamond ATR attachment, are given as Supporting Information. [Fe(bipy)3][(UO2)2(C7)3]·3H2O (1). Pimelic acid (H2C7, 16 mg, 0.10 mmol), UO2(NO3)2·6H2O (33 mg, 0.07 mmol), NH4Fe(SO4)2· 12H2O (15 mg, 0.03 mmol), 2,2′-bipyridine (16 mg, 0.10 mmol), DMF (0.25 mL), and demineralized water (0.5 mL) were placed in a 10 mL tightly closed glass vessel and heated at 140 °C under autogenous pressure, giving dark red crystals of complex 1 within 3 d. The solution was filtered while hot, and the crystals were washed with hot water (14 mg, 25% yield). Anal. Calcd for C51H60FeN6O19U2: C, 38.45; H, 3.80; N, 5.28. Found: C, 38.13; H, 3.41; N, 5.25%. [Cu(phen)2]2[(UO2)3(C7)4(H2O)2]·2H2O (2). Pimelic acid (H2C7, 16 mg, 0.10 mmol), UO2(NO3)2·6H2O (33 mg, 0.07 mmol), Cu(NO3)2· 2.5H2O (7 mg, 0.03 mmol), 1,10-phenanthroline (18 mg, 0.10 mmol), DMF (0.25 mL), and demineralized water (0.5 mL) were placed in a 10 mL tightly closed glass vessel and heated at 140 °C under autogenous pressure, giving dark red crystals of complex 2 within 3 d. The solution was filtered while hot, and the crystals were washed with hot water (20 mg, 36% yield based on U). Anal. Calcd for C76H80Cu2N8O26U3: C, 38.64; H, 3.41; N, 4.74. Found: C, 38.18; H, 3.14; N, 4.69%. [Co(phen)3][(UO2)3(C8)3(O)]·H2O (3). Suberic acid (H2C8, 18 mg, 0.10 mmol), UO2(NO3)2·6H2O (33 mg, 0.07 mmol), Co(NO3)2· 6H2O (10 mg, 0.03 mmol), 1,10-phenanthroline (18 mg, 0.10 mmol), DMF (0.25 mL), and demineralized water (0.5 mL) were placed in a 10 mL tightly closed glass vessel and heated at 140 °C under B

DOI: 10.1021/acs.inorgchem.5b02540 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry Table 1. Crystal Data and Structure Refinement Details chemical formula M (g mol−1) cryst syst space group a (Å) b (Å) c (Å) α (deg) β (deg) γ (deg) V (Å3) Z Dcalcd (g cm−3) μ(Mo Kα) (mm−1) F(000) reflns collcd indep reflns obsd reflns [I > 2σ(I)] Rint params refined R1 wR2 S Δρmin (e Å−3) Δρmax (e Å−3) chemical formula M (g mol−1) cryst syst space group a (Å) b (Å) c (Å) α (deg) β (deg) γ (deg) V (Å3) Z Dcalcd (g cm−3) μ(Mo Kα) (mm−1) F(000) reflns collcd indep reflns obsd reflns [I > 2σ(I)] Rint params refined R1 wR2 S Δρmin (e Å−3) Δρmax (e Å−3)

1

2

3

4

5

6

C51H60FeN6O19U2 1592.96 monoclinic P21/n 12.5658(5) 19.4157(8) 23.6519(12) 90 97.181(4) 90 5725.2(4) 4 1.848 5.970 3080 280 158 10 870 8122 0.045 712 0.038 0.085 1.027 −1.37 1.30 7

C76H80Cu2N8O26U3 2362.65 triclinic P1̅ 9.9979(6) 10.6941(6) 18.5112(13) 85.224(4) 83.546(3) 86.053(4) 1956.3(2) 1 2.005 6.808 1134 87 329 7397 5788 0.115 596 0.075 0.215 1.082 −1.85 2.71 8

C60H62CoN6O20U3 1960.17 triclinic P1̅ 10.8117(5) 12.2223(5) 23.5169(13) 97.787(3) 95.257(3) 90.830(3) 3064.9(3) 2 2.124 8.249 1854 155 217 11 625 9059 0.056 821 0.038 0.097 1.082 −2.33 2.16 9

C60H62N6NiO20U3 1959.95 triclinic P1̅ 10.7649(4) 12.2260(5) 23.6149(9) 97.762(2) 95.283(2) 90.817(2) 3065.3(2) 2 2.123 8.284 1856 149 523 11 627 9745 0.040 821 0.032 0.083 1.077 −2.29 2.22 10

C63H68CoN6O20U3 2002.25 triclinic P1̅ 11.6477(4) 12.0409(2) 23.5965(9) 98.629(2) 97.656(2) 90.808(2) 3240.79(18) 2 2.052 7.803 1902 175 972 12 308 10 680 0.051 857 0.029 0.074 1.098 −1.55 2.20 11

C67H74Cu2N8O16U2 1850.48 triclinic P1̅ 8.1626(4) 13.2785(9) 16.1158(9) 74.996(3) 79.256(4) 83.724(4) 1654.18(17) 1 1.858 5.589 902 85 359 6253 5639 0.039 487 0.027 0.064 1.067 −0.71 1.28 12

C22H28N2O6U 654.49 monoclinic P21/c 7.2124(3) 16.8032(9) 18.7312(7) 90 99.080(2) 90 2241.61(17) 4 1.939 7.281 1256 79 170 4241 3495 0.020 353 0.066 0.162 1.049 −5.13 3.04

C78H110N6NiO25U3 2304.51 monoclinic P21/n 15.0293(4) 24.3182(8) 23.7651(7) 90 91.476(2) 90 8682.9(4) 4 1.763 5.867 4496 258 741 16 426 12 913 0.055 1069 0.046 0.124 1.063 −1.34 2.30

C60H76N6NiO18U2 1704.03 triclinic P1̅ 12.2516(5) 17.7464(10) 30.9207(17) 103.190(2) 91.302(3) 92.067(3) 6537.9(6) 4 1.731 5.299 3336 264 975 24 786 17 075 0.058 1576 0.083 0.233 1.091 −2.29 4.72

C66H84MnN6O22U2 1844.39 triclinic P1̅ 12.9786(9) 13.6451(8) 22.8298(18) 85.394(4) 82.172(3) 67.366(3) 3695.2(5) 2 1.658 4.615 1814 157 669 13 982 9287 0.075 892 0.064 0.173 1.101 −1.54 2.26

C66H86CoN6O23U2 1866.39 monoclinic P21/c 14.6188(3) 22.1607(6) 22.2424(5) 90 94.9287(10) 90 7179.1(3) 4 1.727 4.808 3676 318 590 13 614 11 650 0.041 883 0.074 0.171 1.328 −4.00 4.15

C66H86N6NiO23U2 1866.17 monoclinic P21/c 14.6176(6) 22.2078(8) 22.1851(9) 90 94.911(2) 90 7175.4(5) 4 1.727 4.841 3680 397 710 13 617 11 372 0.058 883 0.069 0.152 1.257 −3.31 3.68

filtered while hot, and the crystals were washed with hot water (14 mg, 31% yield based on U). Anal. Calcd for C22H28N2O6U: C, 40.37; H, 4.31; N, 4.28. Found: C, 40.96; H, 4.38; N, 4.21%. The same complex was obtained in the absence of Mn(NO3)2·4H2O, with all other conditions unchanged. [Ni(bipy)3][(UO2)2(C12)3][UO2(C12)(H2O)2]·H2O (12). Dodecanedioic acid (H2C12, 23 mg, 0.10 mmol), UO2(NO3)2·6H2O (33 mg, 0.07 mmol), Ni(NO3)2·6H2O (10 mg, 0.03 mmol), 2,2′-bipyridine (16 mg, 0.10 mmol), DMF (0.25 mL), and demineralized water (0.5 mL)

washed with hot water (36 mg, 55% yield). Anal. Calcd for C66H86N6NiO23U2: C, 42.48; H, 4.64; N, 4.50. Found: C, 42.34; H, 4.36; N, 4.47%. [UO2(C12)(bipy)] (11). Dodecanedioic acid (H2C12, 23 mg, 0.10 mmol), UO2(NO3)2·6H2O (33 mg, 0.07 mmol), Mn(NO3)2·4H2O (8 mg, 0.03 mmol), 2,2′-bipyridine (16 mg, 0.10 mmol), DMF (0.25 mL), and demineralized water (0.5 mL) were placed in a 10 mL tightly closed glass vessel and heated at 140 °C under autogenous pressure, giving light yellow crystals of complex 11 within 3 d. The solution was C

DOI: 10.1021/acs.inorgchem.5b02540 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry

Figure 1. (top left) View of complex 1. Displacement ellipsoids are drawn at the 50% probability level. Symmetry codes: i = x − 1, y, z; j = x + 1, y, z. (top right) View of the 1D assembly. (bottom left) Packing with ribbons viewed end-on. The uranium coordination polyhedra are colored yellow, and those of iron are orange. Solvent molecules and hydrogen atoms are omitted. (bottom right) View of the hydrogen bonding pattern. Symmetry code: k = −x, 1 − y, 1 − z. were placed in a 10 mL tightly closed glass vessel and heated at 140 °C under autogenous pressure, giving light orange-pink crystals of complex 12 in low yield within 4 d. Crystallography. The data were collected at 150(2) K on a Nonius Kappa-CCD area detector diffractometer13 using graphitemonochromated Mo Kα radiation (λ = 0.710 73 Å). The crystals were introduced into glass capillaries with a protective oil coating (Hampton Research). The unit cell parameters were determined from 10 frames, then refined on all data. The data (combinations of φand ω-scans with a minimum redundancy of 4 for 90% of the reflections) were processed with HKL2000.14 Absorption effects were corrected empirically with the program SCALEPACK.14 The structures were solved by intrinsic phasing with SHELXT15 (except when an isomorphous model could be used), expanded by subsequent difference Fourier synthesis and refined by full-matrix least-squares on F2 with SHELXL-2014.16 All non-hydrogen atoms were refined with anisotropic displacement parameters. The hydrogen atoms bound to oxygen atoms were retrieved from difference Fourier maps when possible, and the carbon-bound hydrogen atoms were introduced at calculated positions; all hydrogen atoms were treated as riding atoms with an isotropic displacement parameter equal to 1.2 times that of the parent atom. Special details are given as Supporting Information. Crystal data and structure refinement parameters are given in Table 1. The molecular plots were drawn with ORTEP-3,17 and the polyhedral representations were drawn with VESTA.18 The topological analyses were conducted with TOPOS.19

Luminescence Measurements. Emission spectra were recorded on solid samples using a Horiba−Jobin−Yvon Fluorolog spectrofluorometer. The powdered complex was pressed between two silica plates, which were mounted such that the faces were oriented vertically and at 45° to the incident excitation radiation. An excitation wavelength of 420 nm was used in all cases, and the emissions were monitored between 450 and 650 nm.

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RESULTS AND DISCUSSION Synthesis. The polycatenated systems previously obtained with the 4,4′-biphenyldicarboxylate ligand comprised hexagonal honeycomb 2D networks and [Ni(bipy/phen)3]2+ counterions with a 2:3:1 metal/ligand/counterion stoichiometry.4 To check for the possibility of analogous architectures with the much more flexible Cn2− dicarboxylates (n = 7−10 and 12), the same stoichiometry was used in the present syntheses so as to favor the formation of hexagonal arrays with triply chelated uranyl cations, but it was not always retained in the final compounds. Solvo-hydrothermal conditions were used, with DMF as organic solvent and a 2:1 water/DMF volume ratio; DMF was previously used as a solvent with some of these H2Cn acids,6c−e while other solvents tested (tetrahydrofuran, acetonitrile, and N-methyl-2-pyrrolidone) proved unsuitable in that they did not give any exploitable crystalline material. D

DOI: 10.1021/acs.inorgchem.5b02540 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry

the total point (Schläfli) symbol {42.6}, and it is analogous to the double-chain structure formed with azelate anions in the presence of trans-1,2-bis(4-pyridyl)ethylene.8c The [Fe(bipy)3]2+ counterions are located between the ribbons, and when viewed down the b axis, they project toward the center of the tetranuclear rings (which have dimensions of ∼12 × 11 Å), with an aromatic ring crossing one ribbon on either side. The water solvent molecules are involved in an interesting pattern since they build a centrosymmetric tetrameric cyclic array with descriptor R44(8) in graph set notation,22 with further bonds to carboxylate oxygen atoms (some of them via another water molecule) uniting two 1D polymeric chains through the formation of R44(16) rings, as shown in Figure 1; the O···O distances are in the range of 2.779(8)−3.020(7) Å (one of the hydrogen atoms bonded to O19 is seemingly not involved in hydrogen bonding). No significant CH···π interaction is present, but as many as 25 H(aromatic)···O(oxo/carboxylate) contacts with H···O distances in the range of 2.38−2.90 Å may indicate the presence of weak CH···O hydrogen bonds,23 as previously observed in the helicates built with C92− and C122− anions.10 These can however only be extremely minor at best compared to the dominant Coulombic interactions and best shape fitting in determining the packing geometry. The stoichiometry in complex 2 is different, with a 3:4 uranium/ligand ratio. The asymmetric unit contains two uranyl ions, one of them (U2) being disordered over two positions close to one another and related by an inversion center, as well as part of the ligands bound to it (see Supporting Information). U1 is triply chelated, with U−O(carboxylate) bond lengths in the range of 2.421(12)−2.512(13) Å [average 2.47(3) Å], while the coordination of U2 is more uncertain due to disorder, with two carboxylate donors either chelating or monodentate in trans positions, and two water molecules (Figure 2). As in 1, one of the ligands connects atoms of the U1 family into linear chains directed along the a axis; the ligand is however not extended, but kinked, with both anti and gauche C−C−C−C torsion angles. Two such chains are further connected to one another by bridges comprising two sinuous ligands and the disordered atom U2, resulting in the formation of a ribbon twice as large as that in complex 1 and with its two halves slightly offset along the b axis; the topology, {42.6}, is the same as in 1 since atoms of the U2 family are only edge-defining. In contrast to compound 1, two smaller counterions are located here inside each hexanuclear ring (dimension ∼30 × 9 Å). The copper(I) cation is in a distorted tetrahedral environment, as usual for this cation,24 with a dihedral angle of 87.09(13)° between the two phen molecules and N−Cu−N angles in the range of 82.9(5)−130.4(5)°. The average Cu−N bond length of 2.026(14) Å is also in agreement with the value of 2.057(3) Å determined from a survey of the CSD.24 Possible paralleldisplaced π-stacking interactions may exist between each cation and those included in the two adjacent ribbons along the b axis, with centroid···centroid distances in the range of 3.56−3.76 Å, and weak CH(aromatic)···O(oxo/carboxylate) hydrogen bonds involving adjacent ribbons may also be present, with H···O distances as short as 2.18 Å. The water molecules are disordered, and their hydrogen atoms were not found, so that nothing definite can be said about the hydrogen bonds they form, apart from that they probably link adjacent chains. Two isomorphous complexes were obtained with the C82− suberate anion, [Co(phen)3][(UO2)3(C8)3(O)]·H2O (3) and [Ni(phen)3][(UO2)3(C8)3(O)]·H2O (4). Although it is not strictly isomorphous, one of the complexes with the C92−

These conditions allowed homogeneous solutions to be obtained when heating at 140 °C, from which crystals deposited during the heating phase when the experiment was successful (several complexes were, however, obtained in low yield). The crystals were filtered off without the solutions being allowed to cool so as to avoid precipitation of the unreacted acid and/or other species, which was often noticed otherwise. The acids were always found to be fully deprotonated in the final products, and no base had to be added to that effect. One of the difficulties in analyzing the results of solvo-/ hydrothermal syntheses is that so little is known of the solution thermodynamics relating to the reactants, especially in mixed solvents. Assuming the Irving−Williams series20 established from complex ion stability constant measurements at 298 K would remain valid at 413 K (140 °C), it is unsurprising to find, for example, that species involving [Mn(bipy)3]2+ cations are much less readily isolated than those of analogues involving heavier transition metals (and that bipy is found coordinated to U in compound 11), while the stabilization of low oxidation states regarded as a characteristic of ligands such as bipy and phen at ambient temperatures could be considered to explain the reduction of Fe(III) and Cu(II) to Fe(II) and Cu(I) in the present experiments (compounds 1, 2, and 6).21 These oneelectron reduction reactions may involve DMF or the carboxylic acids as reducing agents. These conclusions depend on the assumption that the composition of the isolated, crystalline solids directly reflects the speciation in the reactant solutions, but it is clear from the long periods required in some cases for the deposition of crystals that kinetic factors (including hydrolysis of the organic cosolvent) must play a role along with thermodynamic influences. An interesting issue is whether or not the species precipitated are simply those for which the solubility diminishes as a function of temperature, and since this phenomenon is relatively rare, it is quite possible that many of the species isolated in our studies of uranyl systems may represent minor components within the parent solutions. The formation of secondary building units containing oxo or hydroxo ligands resulting from hydrolysis is frequent in uranyl chemistry,1 and bridging oxo ligands are indeed present in complexes 3−5, two of them containing C82− and the third C92− anions, but there is no indication as to why such oxo ions were formed in these cases. Thus, as we noted previously, the pursuit of solvothermal syntheses remains a largely empirical process. Crystal Structures. The 12 complexes obtained are described below in the order of increasing chain length, which appears to be also broadly the order of complexity. Two complexes with the C72− pimelate anion were isolated, [Fe(bipy)3][(UO2)2(C7)3]·3H2O (1) and [Cu(phen)2]2[(UO2)3(C7)4(H2O)2]·2H2O (2), both of them with a 3d cation having undergone reduction (see above). Although the stoichiometry in complex 1, represented in Figure 1, is that which was intended, the geometry is not the 2D honeycomb one. The asymmetric unit contains two inequivalent uranyl ions, both of them tris-chelated with U−O bond lengths in the range of 2.427(4)−2.541(4) Å [average 2.48(3) Å], these values being unexceptional. Two of the ligands have an extended linear form, and they connect uranyl ions into linear chains directed along the a axis, while the third is bent (with alternate anti and gauche C−C−C−C torsion angles). The latter unites two chains into a ribbon bent along its axis, the average equatorial planes of the two uranyl ions making a dihedral angle of 70.76(6)°. The ribbon is ladder-shaped, with E

DOI: 10.1021/acs.inorgchem.5b02540 Inorg. Chem. XXXX, XXX, XXX−XXX

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Figure 3. (top) View of complex 3 (isomorphous to complex 4). Displacement ellipsoids are drawn at the 30% probability level. Symmetry codes: i = −x − 1, 1 − y, 2 − z; j = x + 1, y − 1, z; k = −x, − y, 2 − z; l = x − 1, y, z; m = x − 1, y + 1, z; n = x + 1, y, z. (middle) The 2D assembly viewed edge-on. (bottom) Packing with layers viewed edge-on. The uranium coordination polyhedra are colored yellow, and those of cobalt are orange. Only one position of the disordered part is represented; counterions are omitted in the first two views and solvent molecules and hydrogen atoms are omitted in all views.

Figure 2. (top) View of complex 2. Displacement ellipsoids are drawn at the 30% probability level. Only one position of the disordered parts is represented. Symmetry codes: i = x − 1, y, z; j = 1 − x, 2 − y, − z; k = x + 1, y, z. (middle) View of the 1D assembly. (bottom) Packing with ribbons viewed end-on. The uranium coordination polyhedra are colored yellow, and those of copper are blue; both positions of the disordered uranium atoms are represented as parti-colored yellow and white spheres. Solvent molecules and hydrogen atoms are omitted in all views.

azelate anion, [Co(phen)3][(UO2)3(C9)3(O)]·H2O (5), crystallizes in the same space group and with close unit cell parameters, the introduction of one more carbon atom in the aliphatic chain having no important effect in this case. Since all these complexes display the same overall geometry, only 3 will be described in detail. The asymmetric unit contains three uranyl ions in different environments since, while U3 is triply chelated, U1 and U2 are both in five-coordinate environments with one chelating carboxylate and either two monodentate carboxylates and one oxo atom, or the reverse (Figures 3 and 4; additional views for 4 and 5 are given as Supporting Information). U1, U2, and the μ3-oxo atom O19 thus generate a centrosymmetric tetranuclear secondary building unit of common geometry3o,u,5,9,25 and corresponding to type (i) in the nomenclature of Loiseau et al.1e In particular, such tetranuclear subunits have been found in complexes with C62−−C102− incorporating additional N-donors5 or cucurbi-

Figure 4. View of complex 5. Displacement ellipsoids are drawn at the 50% probability level. Only one position of the disordered parts is represented. Symmetry codes: i = 3 − x, − y, 1 − z; j = x − 1, y + 1, z; k = 2 − x, 1 − y, 1 − z; l = x + 1, y, z; m = x + 1, y − 1, z; n = x − 1, y, z. Views of the 2D assembly and the packing, close to those in 3 and 4, are given as Supporting Information.

turil molecules.9b The average U−O bond lengths of 2.48(5), 2.40(6), and 2.25(4) Å for chelating, monodentate, and μ3-oxo donors, respectively, are unexceptional. U1 and U3 are thus bound to three and U2 to two carboxylate ligands; conversely, F

DOI: 10.1021/acs.inorgchem.5b02540 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry one ligand is bis-chelating with one atom further bridging (O9), the second is chelating/bridging bidentate, and the third is bischelating, so that the first two connect three metal ions and the third only two; all assume irregular, kinked, or sinuous shapes. The tetranuclear units are connected to one another by double carboxylate bridges to form chains running along the [1 1̅ 0] axis, while the atoms of the U3 family and the bis-chelating ligand build chains directed along the a axis. These two differently oriented families of chains are linked to each other by the chelating/bridging bidentate ligands to give a thick (∼28 Å) 2D assembly displaying the tetranuclear units in the center and the isolated U3 atoms on both sides. When viewed down the a axis, these sheets display strongly protruding U3 chains; adjacent sheets along the c axis are interdigitated, while retaining interlayer spaces containing the counterions. Two CH···π interactions may be significant, between hydrogen atoms pertaining either to an aliphatic chain or to the adjoining counterion along the a axis, with H···centroid distances of 2.88 and 2.92 Å and C−H···centroid angles of 137 and 165°, respectively. Some CH···O hydrogen bonds may also be present, with the shorter H···O distance being 2.31 Å. The water molecule, the hydrogen atoms of which have not been found, seems to be hydrogen bonded to carboxylate oxygen atoms from a single layer. Another complex was obtained with C92−, [Cu(bipy)2]2[(UO2)2(C9)3] (6), which does not contain additional oxo bridges. The asymmetric unit in 6 comprises one uranyl ion, and one of the two ligands is disordered around an inversion center (see Supporting Information). The uranium atom is triply chelated, as in 1 and 2, with an average U−O bond length of 2.473(18) Å, and a ladderlike 1D assembly analogous to that in 1 is formed (Figure 5). However, the tetranuclear rings being more elongated (∼16 × 9 Å) and the counterions smaller (as well as their charge), two of the latter can be accommodated within each ring. In contrast to complex 2, the smaller size of the rings here results in the bipy molecules being located outside the rings (while the phen molecules are straddling them in 2). The copper(I) cation is in an environment intermediate between square planar and tetrahedral, with a dihedral angle of 50.09(5)° between the two bipy molecules; the average Cu−N bond length is 2.024(9) Å, and the N−Cu−N angles span the range of 81.20(12)−141.44(13)°. Four possible paralleldisplaced π-stacking interactions may exist between counterions located in the same ring or in rings pertaining to different ribbons, with centroid···centroid distances in the range of 4.10−4.18 Å, and some weak CH(aliphatic)···π (H···centroid distance 2.85 Å) and CH(aromatic)···O(oxo/carboxylate) (shortest H···O distance 2.42 Å) interactions may also be discerned. Four complexes were obtained from sebacic acid, namely, [Ni(bipy)3][(UO2)2(C10)3]·2H2O (7), [Mn(phen)3][(UO2)2(C10)3]·6H2O (8), [Co(phen)3][(UO2)2(C10)3]·7H2O (9), and [Ni(phen)3][(UO2)2(C10)3]·7H2O (10). Complex 7 retains the stoichiometry of the reactants, and it crystallizes with two nearly identical, but crystallographically independent polymeric motifs, each of them containing two independent uranyl ions, both of which are triply chelated (Figure 6). The U−O(carboxylate) bond lengths are in the range of 2.430(13)−2.492(11) Å [average 2.462(15) Å], as usual. For each motif, the asymmetric unit contains two complete ligands and two possessing inversion symmetry; all are bis-chelating and assume a kinked or curved geometry. Atom U2 (U4 in the second motif) is involved in the building of a small

Figure 5. (top) View of complex 6. Displacement ellipsoids are drawn at the 40% probability level. Only one position of the disordered parts is represented. Symmetry codes: i = x, y + 1, z; j = x, y − 1, z; k = −x, 2 − y, 1 − z. (middle): View of the 1D assembly with disordered atoms represented as parti-colored spheres. (bottom) Packing with ribbons viewed end-on. The uranium coordination polyhedra are colored yellow and those of copper are blue. Hydrogen atoms are omitted in all views.

centrosymmetric dinuclear metallacycle, analogous to those previously reported with C82−, although the latter were molecular species.10 U2 is connected to U1 (U4 to U3 in the second motif) by a single ligand, while U1 and U3 are linked to two more uranium atoms through the centrosymmetric ligands. Large decanuclear rings of an extremely elongated shape (∼53 × 12 Å in the widest parts) are thus built, with two smaller rings protruding inside. This gives rise to the formation of a 2D network parallel to (1 0 0), with the point symbol {103}{10}. These rings are sufficiently large to accommodate two counterions, these being located at both ends since the median part of the ring is occupied by the dinuclear units. The two independent motifs are offset so that the packing is of the bump-to-hollow type, the thinner parts corresponding to rows of dinuclear units directed along the b axis. Two solvent water molecules are located inside the dinuclear rings; although water hydrogen atoms were not found, short contacts indicate that each water molecule is involved in hydrogen bonds with oxo or carboxylate acceptors from a single layer. CH(aliphatic)···π (H···centroid distances in the range of 2.88−3.00 Å) and G

DOI: 10.1021/acs.inorgchem.5b02540 Inorg. Chem. XXXX, XXX, XXX−XXX

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Figure 6. (top) View of one of the two independent motifs in complex 7. Displacement ellipsoids are drawn at the 30% probability level. Symmetry codes: i = −x, − y − 1,−z; j = −x, 1 − y, 1 − z; k = −x, 2 − y, 1 − z. (middle) The 2D assembly viewed face-on. (bottom) Packing with layers viewed edge-on. The uranium coordination polyhedra are colored yellow, and those of nickel are green. Counterions are omitted in the first view, and solvent molecules and hydrogen atoms are omitted in all views.

Figure 7. (top) View of complex 8. Displacement ellipsoids are drawn at the 40% probability level. Symmetry codes: i = x − 1, y − 1, z; j = x, y − 1, z + 1; k = x + 1, y + 1, z; l = x, y + 1, z − 1. (middle) View of the 2D honeycomb assembly. (bottom) Packing with layers viewed edgeon and counterions omitted; one layer is singled out in the lower part.

CH(aromatic)···O(oxo/carboxylate) (shortest H···O distance 2.33 Å) interactions may also be present. In contrast to 7, complexes 8−10 contain phen instead of bipy as N-donor. The asymmetric unit in complex 8 contains two uranyl ions and three bis-chelating ligands (Figure 7). The uranium atoms are triply chelated, with U−O bond lengths in the range of 2.443(8)−2.480(8) Å [average 2.460(10) Å]. The stoichiometry matches that initially used during the synthesis, as for 1, 6, and 7, and the assembly formed is two-dimensional with the honeycomb {63} topology (hcb), as was expected. The layers, parallel to (1 1̅ 1̅), display large rings comprising six metal ions as nodes and six dicarboxylate ligands as edges, with largest and smallest dimensions of ∼32 × 20 Å. These rings are slightly larger than those in the complexes with the same topology built from 4,4′-biphenyldicarboxylate ligands (∼27 × 22/23 Å),4 but the 2D → 3D inclined polycatenation that was observed in the latter case is not present here. The layers are not nearly planar as they were in the previous case, but they display a sawtooth shape when viewed down the [1 1 0] axis, with the planar parts, defined by the two ligands in flat conformation, connected to one another by the ligand that is

kinked at both ends, as illustrated by the isolated layer in the packing representation in Figure 7 (bottom), so that the hexanuclear rings have a distorted chair conformation. These layers are tightly packed, and each uranyl ion is located within a ring of the neighboring layer (with one of the oxo bonds threaded through the ring); conversely, each ring is occupied by one uranyl ion from each of the two neighboring layers, but no topologically significant bond crosses the rings. This is thus a borderline case, since only slight modifications of the geometry could have ensured parallel polycatenation. The zigzag shape of the kinked ligand, and the nonplanarity of the rings that results from it, is the main difference with the case of the linear 4,4′biphenyldicarboxylate ligand, and it is probably hampering the occurrence of inclined polycatenation. The counterions are also located within the rings, in which they occupy an off-center position, as illustrated in Figure 8, and the phen molecules H

DOI: 10.1021/acs.inorgchem.5b02540 Inorg. Chem. XXXX, XXX, XXX−XXX

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Figure 8. (top) View of two layers in complex 8 with included counterions. (bottom) Two views of one hexanuclear ring with included counterion and uranyl ions from the two neighboring layers. The uranium coordination polyhedra are colored yellow, and those of manganese are green; the included uranium atoms are represented as yellow spheres.

Figure 9. (top) View of complex 11. Displacement ellipsoids are drawn at the 30% probability level. Only one position of the disordered parts is represented. Symmetry codes: i = x − 2, 3/2 − y, z − 1/2; j = x + 2, 3/2 − y, z + 1/2. (bottom) Packing with chains vertical. Hydrogen atoms are omitted in all views.

mean-square deviation 0.073 Å), the dihedral angle between bipy and this plane being 33.1(9)°. The dicarboxylate ligand, partly disordered, is flat for two-thirds of its length and curved at the extremity, and it unites the uranyl ions into a zigzag chain directed along the [4 0 1] axis. In the case of this neutral species, aromatic interactions are likely to play an important part in determining the packing. Indeed, the chains are arranged so that stacks of bipy molecules involved in parallel-displaced πstacking interactions run parallel to the a axis, as shown in Figure 9 [centroid···centroid distances of 3.758(7)−4.150(7) Å, dihedral angle of 0 or 9.3(6)°]. The bipy molecules thus appear as anchoring parts in these otherwise flexible and weakly interacting polymers. The last complex, [Ni(bipy)3][(UO2)2(C12)3][UO2(C12)(H2O)2]·H2O (12), is also peculiar in that it associates two different polymeric motifs. The asymmetric unit contains four uranium atoms, two of them (U1, U2) in general position and the others (U3, U4) located on inversion centers (U3 being disordered; see Supporting Information) (Figure 10). U1 and U2 are triply chelated [average U−O bond length 2.470(16) Å], and they are part of an anionic [(UO2)2(C12)3]2− assembly with the 2:3 metal/ligand stoichiometry found in the honeycomb arrays. Indeed, the 2D network formed, parallel to (0 1 0), has the point symbol {63} of the hcb lattice, but it appears as a deeply furrowed one. The kinked shape of the ligands results in the aliphatic chains of three of them being located inside the hexanuclear ring, giving the latter a triskelion shape when viewed down the b axis. However, the 2D assembly is far from being planar, and the rings are quite convoluted, as shown by the edge-on view in Figure 10, in which each ring corresponds to four successive uranyl ions, two of them close to

protrude into the rings of adjacent layers. Apart from dominant Coulombic interactions, CH(aliphatic)···π (H···centroid distances in the range of 2.66−3.00 Å) and CH(aromatic)··· O(oxo/carboxylate) (shortest H···O distance 2.33 Å) interactions may also be present. The hydrogen atoms of the water molecules (some of them disordered) were not found, and the hydrogen-bonding scheme is thus uncertain. Although they crystallize in a different space group, the isomorphous complexes 9 and 10 display an overall arrangement similar to that in 8, with layers parallel to (2 0 1) (see figures in Supporting Information), so that these complexes will not be described further, except to note that the seven solvent water molecules build a very intricate hydrogen bond pattern that unites the layers into a 3D architecture. Of the two complexes obtained with dodecanedioate, one is peculiar in that it is the only compound in this series that does not include 3d cations. The asymmetric unit in [UO2(C12)(bipy)] (11) comprises a single uranyl ion that is chelated by two carboxylate groups and the bipy molecule (Figure 9). Although the affinity of uranyl is greater for carboxylates than for the neutral bipy, the latter is often found to act as a coligand, as in the present case.26 Its regioisomer 4,4′bipyridine was used in previous studies, but its bridging nature makes it an utterly different coligand.5,8c The U−O(carboxylate) and the U−N bond lengths are unexceptional, with average values of 2.449(16) and 2.65(3) Å, respectively. The uranium hexagonal bipyramidal environment is however very distorted, with atoms N1 and N2 displaced by 0.49(4) and 0.77(6) Å on either side of the mean plane defined by the uranium atom and the four carboxylate oxygen donors (rootI

DOI: 10.1021/acs.inorgchem.5b02540 Inorg. Chem. XXXX, XXX, XXX−XXX

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Figure 10. (top left) View of complex 12. Displacement ellipsoids are drawn at the 30% probability level. Counterions, solvent molecules, and carbon-bound hydrogen atoms are omitted. Symmetry codes: i = x − 1/2, 3/2 − y, z + 1/2; j = x − 1, y, z; k = −x, 1 − y, − z; l = −x, 1 − y, 1 − z; m = x + 1/2, 3/2 − y, z − 1/2; n = x + 1, y, z. (top right) View of the 2D assembly. (bottom left) The 2D assembly viewed edge-on. (bottom right) Packing including counterions. The uranium coordination polyhedra are colored yellow, and those of nickel are green. Only one position of the disordered parts is represented. Solvent molecules and hydrogen atoms are omitted from the last three views.

the mean plane and the others located alternately above and below it. As a result, the layers are stacked in a bump-to-hollow way. Atoms U3 and U4 are also hexacoordinate in their equatorial plane, being bound to two chelating carboxylate groups in trans positions, and two water molecules. They are part of neutral undulating chains [UO2(C12)(H2O)2] running along the c axis, which wind their way between the layers without ever crossing them. Although unusual, the coexistence of two different polymeric species within the same lattice has previously been observed in uranyl−organic assemblies.27 The counterions are located in the intralayer spaces, within the cavities defined by three carboxylate ligands bound to the same uranyl ion, which has the shape of an open cage (Figure 11). These cavities are akin to those in the helicates formed by the same ligand,10 but, instead of the three C122− anions bridging only two uranyl ions located on a trigonal axis, they are divergent here and connect the central uranium atom to three metallic centers while wrapping around the counterion. As in the previous cases, the interactions between cation and anion are mainly Coulombic and, in this case, best shape fitting may be very important too (with a possible structure-directing effect of the cation). Only one CH(aliphatic)···π (H···centroid distance 2.87 Å) and some CH(aromatic)···O(oxo/carboxylate) (shortest H···O distance 2.31 Å) interactions may be found. The water molecules, both coordinated and free, are hydrogen bonded to carboxylate oxygen atoms [O···O

Figure 11. Inclusion of the counterion in the intralayer cavity (bold lines) in complex 12. The uranium coordination polyhedra are colored yellow, and that of nickel is green.

distances in the range of 2.359(17)−3.082(10) Å], thus creating a network uniting the layers and chains into a 3D structure. Luminescence Properties. Emission spectra under excitation at a wavelength of 420 nm, a value suitable for uranyl excitation,28 were recorded in the solid state for all compounds. The spectra for compounds 2 and 11 are shown in Figure 12, and all the others are given as Supporting Information. Uranyl emission is characterized by the vibronic J

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assumed that transfer of the uranyl excitation energy to the 3T2g excited state of the Ni(II) ion, followed by its radiative decay, must have occurred. Thus, it is argued that the same could be true in the cases of complexes 4 and 7, with complex 12 providing an interesting case where the energy transfer does not occur. In complex 10, there appears to be a very weak uranyl emission but again no energy transfer to Ni(II).

■

CONCLUSIONS Twelve uranyl complexes with long-chain aliphatic α,ωdicarboxylates have been synthesized and characterized by their crystal structure and their emission spectrum. All were obtained under solvo-hydrothermal conditions from 2:3 uranyl/H2Cn mixtures, in the presence of 3d-block metal ions and bipy or phen donors. The presence of [M(bipy/phen)3]2+ counterions is observed in all cases but that of the neutral complex 11 in which bipy is coordinated to uranium, and those in which reduction of Cu(II) occurred to give [Cu(bipy/ phen)2]+ cations (2 and 6). An extensive study of these acids had previously been conducted in which 4,4′-bipyridine, 1,2bis(4-pyridyl)ethane, and trans-1,2-bis(4-pyridyl)ethylene were used as additional ligands, lattice guests, or counterions (when protonated).5,8c Considering the flexibility of these aliphatic dicarboxylate ligands, it is not surprising that modifications in the experimental procedure such as those between the latter series of experiments and the present one result in the isolation of quite different species. Three coordination modes were previously observed, chelating, chelating and bridging (or bridging tridentate), and bridging bidentate. All these are present here also, but the bis-chelating mode is by far the most common since the other two are only found in complexes 3−5, the latter being the only complexes in this series that involve the formation of tetranuclear secondary building units built around μ3-oxo anions; it may be assumed that this close arrangement of uranyl ions favors bridging coordination modes. Several analogous tetranuclear subunits were also found in the previously reported series, with the same or slightly different polyhedra arrangements, and they were all associated with the presence of bridging carboxylates.5,8c In all the other complexes, the uranyl ions are isolated and most often triply chelated, a coordination mode that was also observed in the previous series. This coordination mode has also previously been found in molecular complexes containing two metal cations and three ligands with triple-stranded helicate geometry involving C92− and C122−.10 When the species formed are polymeric, this 2:3 metal/ligand stoichiometry does not necessarily result in the formation of the honeycomb networks, since the polymers formed can be 1D and ladderlike, as in complexes 1 (C72−) and 6 (C92−), or display a 2D tessellation of di- and decanuclear rings as in complex 7 (C102−). Honeycomb topologies are found in complexes 8−10 (C102−), in which the main difference with 7 is replacement of bipy by phen donors, thus showing the structure-directing effect exerted by counterions. The large hexanuclear rings in these latter cases are chairshaped, and they contain one counterion and two uranyl ions from neighboring sheets; no interpenetration is however observed. With the even longer ligand C122−, a 2D assembly of similar topology is formed (12), but the rings adopt a very convoluted shape. This points to the intermediate nature of this species, which has the hcb topology, but displays local features matching those in the helicates obtained with the same ligand. The dominant interactions in all these complexes in the solid state are Coulombic,31,32 and it is only in the neutral complex

Figure 12. Emission spectra of compounds 2 and 11. The excitation wavelength was 420 nm.

progression corresponding to the S11 → S00 and S10 → S0ν (ν = 0−4) electronic transitions.29 However, more or less complete quenching by transition metal cations, probably through energy transfer to the d−d excited state followed by nonradiative decay, is well documented,2a,3n,p,u,v,30 and it occurs in compounds 1, 3, 5, 6, 8, 9, and 10. It is only for the coppercontaining complex 2, the uranyl-only species 11 and, in a lesser measure, the nickel-containing complex 12 that wellresolved spectra are observed. The maxima positions are at 481, 501, 523, and 547 nm in 2, 487, 507, 529, and 553 nm in 11, and 480, 499, and 521 nm in 12. The spectra of complexes 2 and 12 are thus nearly identical, although the emission intensity in the latter is much weaker, and that of 11 displays a redshift of ∼6 nm. The nickel-containing complexes 4 and 7 are peculiar since they display a very broad and barely resolved emission band in the 500−590 nm range. A quite similar spectrum was previously obtained3u for another uranyl complex containing [Ni(bipy)3]2+ counterions, where, given that the emission spectrum resembled the absorption spectrum of [Ni(bipy)3]2+, while no emission could be observed for [Ni(bipy)3](NO3)2 when directly irradiated at 420 nm (nor was there literature evidence found for emission under other conditions), it was K

DOI: 10.1021/acs.inorgchem.5b02540 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry 11 formed by uranyl alone with C122− and bipy coligands that parallel-displaced π-stacking interactions are clearly important in determining the packing. All these results show that, although it has been already much investigated in uranyl chemistry, this family of Cn2− ligands, remarkable by the variation of the aliphatic chain length as only parameter, is still susceptible to yield complexes of original geometry depending on the n value and the nature of additional species present (as well as possibly the stoichiometry of the reactants and the temperature, which have been kept constant here). The structure-directing effects of the counterions are so subtle as to prevent specific prevision of the final species formed, these being extremely varied and encompassing molecular complexes of unprecedented form as well as 1D and 2D assemblies, some of them of quite intricate geometry. A striking illustration of this is found in the isolation of a polymeric complex of C92− when [M(phen)3]2+ is the countercation but of triple-helicate species when the countercation is [M(bipy)3]2+ and vice versa for C122−, while none of these cations seems to be suitable for helicate formation with the intermediate-sized C102−. All these results provide yet further evidence of the remarkable variety of factors that are open to exploitation in solvothermal syntheses.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.5b02540. Crystal structure refinement details, additional figures, emission and IR spectra. (PDF) X-ray crystallographic information, including structures. (CIF) X-ray crystallographic information, including structures. (CIF)

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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REFERENCES

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DOI: 10.1021/acs.inorgchem.5b02540 Inorg. Chem. XXXX, XXX, XXX−XXX

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DOI: 10.1021/acs.inorgchem.5b02540 Inorg. Chem. XXXX, XXX, XXX−XXX