Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 140 (2015) 437–443

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Structure, photochemistry and magnetic properties of tetrahydrogenated Schiff base chromium(III) complexes Bin Liu ⇑, Jie Chai, SiSi Feng, BinSheng Yang ⇑ Institute of Molecular Science, Key Laboratory of Chemical Biology of Molecular Engineering of Education Ministry, Shanxi University, Taiyuan 030006, China

h i g h l i g h t s

g r a p h i c a l a b s t r a c t

 Five tetrahydrogenated Schiff base NH

Cr(III) complexes were composed.  The stability relates to the chelate

O

effect of rings.  The photochemistry reaction was studied.  Complex 5 exhibits a strong antiferromagnetic coupling.

Cr

H 2N

O

Cr

O NH2

3

Keywords: Chromium(III) Tetrahydrogenated Schiff base Kinetics Photochemistry Chelate effect Magnetism

O NH2

2

NH

NH Cr

O H 2N

O NH2

4

NH

Cr

O O

O O

O Cr

O NH

NH

5

a b s t r a c t Four mononuclear chromium(III) complexes [Cr(L(1))(en)]Br0.3Cl0.7 (1), [Cr(L(1))(pr)]Cl (2), [Cr(L(2)) (en)]ClO4 (3), [Cr(L(2))(pr)]Cl (4) along with one dinuclear l-methoxo [Cr(l-OMe)(L1)]2 (5) were synthesized (en = 1,2-ethanediamine, pr = 1,3-diaminopropane H2L(1) = Tetrahydrosalen = H2[H4]salen = N,N0 -bis (2-hydroxybenzyl)-1,2-ethanediamine, H2L(2) = Tetrahydrosalpr = H2[H4]salpr = N,N0 -bis(2-hydroxybenzyl)-1,3-diaminopropane). The competitive reactions in the presence of EDTA were carried out and the first-order rate constants k(1) = (5.2 ± 0.2)  103 h1 < k(2) = (6.7 ± 0.3)  103 h1 < k(3) = (8.0 ± 0.1)  103h1 < k(4) = (9.5 ± 0.2)  103 h1 were obtained by spectroscopic measurements. In addition, photo-induced decomposition was monitored under irradiation of xenon lamp. The sequence of first-order rate constants is k0 (1) = (4 ± 0.1)  104 s1 < k0 (2) = (6 ± 0.3)  104 s1 < k0 (3) = (1.1 ± 0.2)  103 s1 < k0 (4) = (1.4 ± 0.2)  103 s1, which is in accordance with that of kinetics studies with EDTA. Dinuclear complex 5 exhibits a strong antiferromagnetic coupling with the J = 10.8 cm1. Ó 2015 Elsevier B.V. All rights reserved.

Introduction Transition metal complexes with oxygen and nitrogen donor Schiff bases are of particular interest because of their unusual con-figurations, structural lability and sensitivity to molecular environments as functional materials [1]. Although the tetradentate Schiff-base ligands containing N2O2 donors are easy to coordinate to transition- and non-transition-metal ions, the coordination ⇑ Corresponding authors. Tel.: +86 351 7016358. E-mail addresses: [email protected] (B. Liu), [email protected] (B. Yang). http://dx.doi.org/10.1016/j.saa.2015.01.012 1386-1425/Ó 2015 Elsevier B.V. All rights reserved.

H2N

NH2

NH

H 2N

Article history: Received 17 November 2014 Received in revised form 30 December 2014 Accepted 11 January 2015 Available online 17 January 2015

Cr

NH

O

i n f o

O

1

NH

a r t i c l e

NH

NH

NH

geometries afforded to metal centers by these multidentate species has sustained their widespread interest over the past 150 years. It should be noted that hydrogenation of tetradentate Schiff bases will not only increase the donor strength of the internal nitrogen donors, but also increase the ligand flexibility [2]. Taylor and Reglinski have studied the effect of donor groups and geometry on the redox potential of tetrahydrogenated Schiff base complexes by systematically increasing the size of the polymethylene chain between the internal nitrogen donors [1,3]. Although the transition metal complexes of tetrahydrogenated ligand H2[H4]salen [4] and H2[H4]Salpr [3] (H2[H4]salen = N,N0 -bis(2-hydroxybenzyl)-1,2-eth-

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B. Liu et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 140 (2015) 437–443

anediamine, H2[H4]salpr = N,N0 -bis(2-hydroxybenzyl)-1,3-diaminopropane) have been fully studied, few Cr(III) complexes with salen2, [H4]salen2, salpr2 or [H4]Salpr2 have been reported [5–7]. It is well known that Cr(III) complexes with Schiff bases and theirs derivatives play an important role in catalytic reactions, photochemistry, artificial nucleases, carbohydrate metabolism. Interested by the thermodynamic, kinetic, and electronic properties of Cr(III) complexes with salicylate and en ligands [8], we initiated an investigation of oligomeric Cr(III) compounds containing the tetrahydrogenated ligand [H4]salen2 or [H4]Salpr2 and ethanediamine (en) or 1,3-diaminopropane (pr). The use of Zn as a reducing agent can turn the inert Cr(III) to reactive Cr(II). The combination of these polydentate ligands can lead to the formation of stable chelates. In this paper five tetrahydrogenated Schiff base Cr(III) complexes were synthesized for the first time. The possible steric effects including the number of chelate rings and the size of chelate ring upon the kinetics stability and photochemistry reaction were investigated by spectroscopic measurements. The magnetic properties of a dinuclear Cr(III) complex were also explored. Experimental General procedure Unless otherwise stated all chemicals were commercially obtained and used without further purification. All manipulations were performed under aerobic conditions. The ligands H2L(1) and H2L(2) (H2L(1) = Tetrahydrosalen, H2L(2) = Tetrahydrosalpr) were obtained from methods given in the literature (see the ESI) [1c]. All other chemicals were of analytical grade. 1 H NMR spectra were recorded on Bruker-300 MHz spectrometers, the chemical shifts (d) were reported as ppm in DMSO. ESI-MS spectra were recorded on an Agilent 6520 Accurate-Mass Q-TOF LC/MS mass spectrometer. UV–visible (UV–Vis) spectra were measured with a Varian 50 BIO spectrophotometer. Elemental analyses were measured on a Vario EL III analyzer. IR spectra were recorded with a Bruker TENSOR 21 FT-IR spectrophotometer. Synthesis [Cr(L(1))(en)]Br0.3Cl0.7CH3OH (1), [Cr(L(1))(l-OMe)]22CH3OH (5) Complexes 1 and 5 were formed from the same batch. H2L(1) (136 mg, 0.5 mmol), CrCl36H2O (133 mg, 0.5 mmol) and granular (Mesh size 20) zinc (0.10 g, 1.5 mmol) were put in flask, and methanol (20 mL) was added. After an hour’s refluxing, ethanediamine (en, 1 mL, 15.0 mmol) was added to the solution; the solution was kept stirring and refluxing for 0.5 h, purple precipitate was obtained. Filtered through the funnel, purple minicrystal and aubergine filtrate were obtained. The purple minicrystal was redissolved by addition of ethanol: H2O = 1:1, then KBr was added to the solution. The solution was filtered through the funnel, plenty of block purple crystals (complex 1) were obtained in the filtrate after a few days (yield > 70%). The aubergine filtrate was placed over night, and another aubergine crystal 5 was obtained (yield < 10%). Interestingly, the yield of complex 1 or 5 was affected by the amount of added en solution: the more en was added, the more 1 was produced. Anal. Cacld. for C19H30Br0.3Cl0.7CrN4O3 (1): C, 49.50; H, 6.56; N, 12.15. Find: C, 49.38; H, 6.49; N, 12.19. Anal. Cacld. for C36H52Cr2N4O9 (5): C, 54.81, H, 6.64, N, 7.10. Find: C, 54.63, H, 6.42, N, 7.22. IR: 1: 3400, 3113, 1595, 1480, 1275, 1053, 762, 628 cm1; 5: 3176, 2925, 1595, 1478, 1290, 1064, 758 cm1.

and methanol (20 mL) was added. After an hour’s refluxing, 1,3diaminopropane (pr, 2 mL, 24.0 mmol) was added to the solution, the solution was kept stirring and refluxing for 0.5 h, purple precipitate was obtained. Filtered through the funnel, purple minicrystal (complex 2) was obtained. Anal. Cacld. for C20H32ClCrN4O3: C, 51.78; H, 6.95; N, 12.08. Find: C, 51.74; H, 6.99; N, 12.11. ESI-MS spectra: m/z = 396.16 (Fig. S4), [M]+; [M]+ calculated: 396.16. IR: 3271, 3113, 2930, 1595, 1480, 1276, 1080, 760 cm1. [Cr(L(2))(en)]ClO4 (3) H2L(2) (143 mg, 0.5 mmol), CrCl36H2O (133 mg, 0.5 mmol) and granular (Mesh size 20) zinc (0.10 g, 1.5 mmol) were refluxing in methanol (20 mL) for an hour, then en (1 mL, 15.0 mmol) was added to the solution, the solution was kept stirring and refluxing for 0.5 h, purple precipitate was obtained. The solution was filtered through the funnel; purple minicrystal and aubergine filtrate were obtained. Sodium perchlorate (0.12 g, 1.0 mmol, note: perchlorate salts are explosive) was added to the aubergine filtrate carefully in room temperature, purple crystal were obtained (complex 3) over night. Anal. Cacld. for C19H28ClCrN4O2: C, 52.96; H, 6.32; N, 13.00. Find: C, 52.98; H, 6.218; N, 13.03. IR: 3303, 3244, 1595, 1479, 1286, 1107, 766 cm1. [Cr(L(2))(pr)]ClCH3OH (4) H2L(2) (143 mg, 0.5 mmol), CrCl36H2O (133 mg, 0.5 mmol) and granular (Mesh size 20) zinc (0.10 g, 1.5 mmol) were refluxing in methanol (20 mL) for an hour, then pr (2 mL, 24 mmol) was added to the solution, keep refluxing for 0.5 h and purple precipitate was obtained. The result solution was filtered and the aubergine filtrate was placed, purple crystal (complex 4) was obtained over night. Anal. Cacld. for C21H34ClCrN4O3: C, 52.77; H, 7.17; N, 11.72. Find: C, 52.79; H, 7.14; N, 11.69. IR: 3107, 2934, 1596, 1482, 1278 cm1. X-ray structure determination For each sample, a single crystal with suitable dimensions for Xray diffraction analyses was mounted on a glass rod, the crystal data were collected with a Siemens (Bruker) SMART CCD diffractometer using monochromated Mo-Ka radiation (0.71073 Å) at 293 K. In all cases intensity data were measured by thin-slice xor x- and u-scans. The method used to solve the structure was direct method and the structure was further expanded using Fourier difference techniques with the SHELXTL-97 program package [9]. Absorption corrections were carried out using the SADABS program supplied by Bruker [10]. The anisotropic refinement was applied for all non-hydrogen atoms while hydrogen atoms in all samples were included in idealized positions and their Uiso values were set to ride on the Ueq values of the parent carbon, nitrogen or oxygen atoms. Details of the crystallographic data collection, structural determination and refinement are summarized in Table 1. Selected bond lengths (Å) and angles (°) of 1, 3, 4, and 5 are shown in Table 2. For crystallographic data in CIF format, see the ESI. CCDC reference numbers: 712642, 913849, 1002820, 1002821. Photochemical stability 1  103 M complex 1–4 in Tris–HCl buffer (0.01 M, pH = 7.4) was exposed to light of xenon lamp (CEL-S500/350, 50 mW/cm2, AM 1.5) in methanol, 293 K for hours. This course was monitored by UV–Vis spectra. Magnetic measurements

[Cr(L(1))(pr)]Cl (2) H2L(1) (136 mg, 0.5 mmol), CrCl36H2O (133 mg, 0.5 mmol) and granular (Mesh size 20) zinc (0.10 g, 1.5 mmol) were put in flask,

Variable-temperature magnetic susceptibility on a crystalline sample was performed on a Quantum Design MPMS-XL SQUID

439

B. Liu et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 140 (2015) 437–443 Table 1 Crystal data and refinement details for complex 1, 3, 4 and 5. Complex

1

3

4

5

Formula Formula weight Crystal system space group a/Å b/Å c/Å a (°) b (°) c (°) V/Å3 Z Density/g cm3 F(0 0 0) h h, k, l Tot. Uniq. Data R(int) Nreflections, Nparameter GOF on F2 R1[I > 2s (I)], wR2

C19H30Br0.30Cl0.70CrN4O3 463.26 Orthorhombic 2(1)2(1)2(1) 8.2150(5) 13.2027(8) 19.8414(13) 90 90 90 2152.0(2) 4 1.430 970 2.57–25.02 7/9, 9/15, 23/22 8094/805/0.0629 3805/255 0.998 0.0579, 0.0965

C19H28ClCrN4O6 495.90 Triclinic P  1 9.6977(8) 11.4352(10) 11.8037(12) 114.782(2) 104.2810(10) 99.5480(10) 1096.44(17) 2 1.502 518 3.02–25.01 11/11, 13/13, 14/14 3850/3850/0.0000 3850/324 1.126 0.0802, 0.2294

C21H34ClCrN4O3 477.97 Monoclinic, P2(1)/c 7.5886(8) 12.1186(13) 25.557(2) 90 97.441(2) 90 2330.5(4) 4 1.362 1012 2.71–25.02 5/9, 13/14, 30/30 18588/4092/0.1393 4092/271 1.102 0.1288, 0.2967

C36H52Cr2N4O9 788.82 Monoclinic, P2(1)/c 7.6249(9) 13.7319(12) 19.087(2) 90 100.895(2) 90 1962.4(4) 2 1.335 832 1.84–25.01 8/9, 16/13, 22/21 9620/3450/0.0522 3450/254 1.043 0.0612, 0.1605

Table 2 Selected bond lengths (Å) and angles (°) of 1, 3, 4, and 5. Bond lengths

Bond angles

Bond angles

Bond angles

Compound 1 Cr1–O1 Cr1–O2 Cr1–N1 Cr1–N2 Cr1–N3 Cr1–N4

1.900(4) 1.927(4) 2.100(4) 2.070(4) 2.097(4) 2.105(4)

O1-Cr1-O2 O1-Cr1-N2 O2-Cr1-N2 O1-Cr1-N3 O2-Cr1-N3

90.45(17) 93.21(17) 91.62(16) 92.95(19) 87.67(17)

N2-Cr1-N3 O1-Cr1-N1 O2-Cr1-N1 N2-Cr1-N1 N3-Cr1-N1

173.80(18) 90.03(17) 173.27(18) 81.65(18) 99.00(18)

O1-Cr1-N4 O2-Cr1-N4 N2-Cr1-N4 N3-Cr1-N4 N1-Cr1-N4

173.55(18) 88.37(17) 93.16(17) 80.67(18) 91.89(17)

Compound 3 Cr1–O2 Cr1–O1 Cr1–N1 Cr1–N2 Cr1–N3 Cr1–N4

1.920(5) 1.931(5) 2.124(6) 2.090(6) 2.108(6) 2.112(6)

O2-Cr1-O1 O2-Cr1-N2 O1-Cr1-N2 O2-Cr1-N3 O1-Cr1-N3

92.7(2) 91.8(2) 87.2(2) 85.5(2) 95.5(2)

N2-Cr1-N3 O2-Cr1-N4) O1-Cr1-N4 N2-Cr1-N4 N3-Cr1-N4

176.4(2) 86.3(2) 176.6(2) 96.1(2) 81.2(2)

O2-Cr1-N1 O1-Cr1-N1 N2-Cr1-N1 N3-Cr1-N1 N4-Cr1-N1

176.1(2) 89.3(2) 91.6(2) 91.0(2) 91.6(2)

Compound 4 Cr1–O2 Cr1–O1 Cr1–N1 Cr1–N2 Cr1–N3 Cr1–N4

1.930(8) 1.931(8) 2.128(9) 2.083(10) 2.075(11) 2.065(11)

O2-Cr1-O1 O2-Cr1-N4 O1-Cr1-N4 O2-Cr1-N3 O1-Cr1-N3

87.6(3) 88.2(4) 92.5(4) 91.6(4) 177.8(4)

N4-Cr1-N3 O2-Cr1-N2 O1-Cr1-N2 N4-Cr1-N2 N3-Cr1-N2

85.4(5) 89.9(4) 93.7(4) 173.4(4) 88.3(4)

O2-Cr1-N1 O1-Cr1-N1 N4-Cr1-N1 N3-Cr1-N1 N2-Cr1-N1

175.3(3) 89.7(3) 88.0(4) 91.0(4) 94.2(4)

Compound 5 Cr1–O2 Cr1–O1 Cr1–O3#1 Cr1–O3 Cr1–N1 Cr1–N2

1.943(4) 1.954(3) 1.958(4) 1.968(4) 2.068(5) 2.078(4)

O2-Cr1-O1 O2-Cr1-O3#1 O1-Cr1-O3#1 O2-Cr1-O3 O1-Cr1-O3

90.58(15) 94.39(16) 92.81(16) 172.64(16) 92.60(16)

O3#1-Cr1-O3 O2-Cr1-N1 O1-Cr1-N1 O3#1-Cr1-N1 O3-Cr1-N1

78.82(19) 92.70(17) 91.25(17) 171.78(17) 93.87(17)

O2-Cr1-N2 O1-Cr1-N2 O3#1-Cr1-N2 O3-Cr1-N2 N1-Cr1-N2

90.25(16) 174.15(19) 92.90(17) 87.27(16) 82.93(18)

magnetometer. The susceptibility measurement was performed in the 300–1.8 K temperature range with an applied field of 1 kOe. Data were corrected for the sample holder and diamagnetism was estimated from Pascal constants. X-ray powder diffraction was performed on bulk samples prior to magnetic studies. Results and discussion Synthetic and structural studies Both ligands N,N0 -bis(2-hydroxybenzyl)-1,2-ethanediamine (H2L(1)) and N,N0 -bis (2-hydroxybenzyl)-1,3-diaminopropane (H2L(2)) were prepared as previously reported and were isolated in good yields [1c]. The first step of the present work aimed at studying the coordination of H2L(1) and H2L(2) toward Cr(III) salt for the obtainment of well-defined Cr(III) metal complexes. Thus,

the reaction of H2L(1) (1.0 equivalents), excess en with CrCl36H2O in methanol affords the mononuclear complex 1 in 70% yield (Scheme 1) and binuclear complex 5 (