Accepted Manuscript Temperature-dependent self-assembly of Near-infrared (NIR) luminescent Zn2Ln and Zn2Ln3 (Ln = Nd, Yb or Er) complexes from the flexible Salen-type Schiff-base ligand Tiezheng Miao, Zhao Zhang, Weixu Feng, Peiyang Su, Heini Feng, Xingqiang Lü, Daidi Fan, Wai-Kwok Wong, Richard A. Jones, Chengyong Su PII: DOI: Reference:

S1386-1425(14)00726-4 http://dx.doi.org/10.1016/j.saa.2014.04.153 SAA 12117

To appear in:

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy

Received Date: Revised Date: Accepted Date:

9 January 2014 21 March 2014 23 April 2014

Please cite this article as: T. Miao, Z. Zhang, W. Feng, P. Su, H. Feng, X. Lü, D. Fan, W-K. Wong, R.A. Jones, C. Su, Temperature-dependent self-assembly of Near-infrared (NIR) luminescent Zn2Ln and Zn2Ln3 (Ln = Nd, Yb or Er) complexes from the flexible Salen-type Schiff-base ligand, Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy (2014), doi: http://dx.doi.org/10.1016/j.saa.2014.04.153

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Temperature-dependent

self-assembly

of

Near-infrared (NIR) luminescent Zn2Ln and Zn2Ln3 (Ln = Nd, Yb or Er) complexes from the flexible Salen-type Schiff-base ligand Tiezheng Miao a, Zhao Zhanga, Weixu Fenga, Peiyang Sua, Heini Fenga, Xingqiang Lüa*, Daidi Fana, Wai-Kwok Wongb, Richard A. Jonesc, Chengyong Sud

a

Shaanxi Key Laboratory of Degradable Medical Material, Shaanxi Key Laboratory of

Physico-inorganic Chemistry, Northwest University, Xi’an 710069, Shaanxi, China b

Department of Chemistry, Hong Kong Baptist University, Waterloo Road, Kowloon Tong,

Hong Kong, China. c

Department of Chemistry and Biochemistry, The University of Texas at Austin, 1 University

Station A5300, Austin, TX 78712-0165, United States d

MOE Laboratory of Bioinoragnic and Synthetic Chemistry/KLGH EI of Environment and

Energy Chemistry, School of Chemistry and Chemical Engineering, Sun Yat-Sen University, Guangzhou 510275, Guangdong, China

To whom correspondence should be addressed. Tel./fax: +86-029-88302312 E-mail: [email protected]

1

Abstract Through

the

self-assembly

of

the

precursor

[Zn(L)(MeCN)]

(H2 L

=N,N’-bis(3-methoxy-salicylidene)cyclohexane-1,2-diamine ) with LnCl3·6H2O (Ln = La, Nd, Yb, Er or Gd) and NaN3 in alcohol-containing solutions, two series of mixed anions-induced Zn2Ln-arrayed complexes [Zn2(L)2(MeOH)ClLn(N3)]·Cl (Ln = La, 1; Ln = Nd, 2; Ln = Yb, 3; Ln

=

Er,

4

or

Ln

=

Gd,

5)

and

Zn2Ln3-arrayed

complexes

[Zn2(L)3Cl2(µ2-OH)(µ3-OH)2 Ln3(N3)2] (Ln = La, 6; Ln = Nd, 7; Ln = Yb, 8; Ln = Er, 9 or Ln = Gd, 10) are obtained at room temperature or under reflux, respectively. In contrast to Zn2Ln-arrayed complexes with the two Zn2+ ions in the inner cis-N2O2 cores and one Ln3+ ion in the outer O2O2 moieties, the demetalation of partial precursors leads to the selective exchange of Zn2+ centers for the Ln3+ ions for the formation of novel heterometallic Zn2Ln3-arrayed complexes with the Ln3+ ions in both the inner cis-N2O2 core and the outer O2O2 moieties of the ligands. The result of their photophysical properties shows that the characteristic near-infrared (NIR) luminescence of Nd3+ or Yb3+ ion has been sensitized from the excited state (both 1 LC and 3LC) of the ligand H2L, while relatively lower quantum yields for Zn2Ln3-arrayed complexes than those for Zn2 Ln-arrayed complexes, correspondingly, should be due to the luminescent quenching with the involvement of OH- oscillators arround the Ln3+ ions.

Keywords: Heterometallic Zn2Ln-arrayed or Zn2Ln3-arrayed complexes; Mixed anions; Temperature dependence for demetalation; Sensitization of NIR luminescence

2

1. Introduction Much recent efforts have been devoted into near-infrared (NIR) luminescent Ln3+ (Ln = Nd, Yb or Er) complexes because of their potential applications in NIR organic light-emitting diodes (OLEDs) [1], tele-communication [2] and bio-analysis [3]. However, due to forbidden parity from f-f transitions, the absorption coefficients of these Ln3+ ions are normally very low, which needs the introduction of chromophores to sensitize the NIR luminescence of Ln3+ ions indirectly [4]. Compared with cyclic [5] or acyclic [6] aromatic ligands as the sensitizers for Ln3+ NIR luminescence, d-block transition metal complexes [7] are more superior, because they can display the desired excited state (1LC, 3LC, 3MLCT or 3LMCT) and the desired absorption wavelength. Moreover, from the viewpoint of efficient sensitization of Ln3+-based NIR luminescence, the choice of suitable chromophores remains an actual challenge, which requires the realization of the energy level’s match of the excited state of the chromophores to the Ln3+ ions’ excited state [8] besides the complete avoidance or decrease of the luminescent quenching effect arising from OH-, CH- or NH-containing oscillators around the Ln3+ ions [9]. In our or others recent reports, series of discrete or polymeric complexes have been obtained from the self-assembly of 3d Zn2+ and 4f Ln3+ ions with the Salen-type Schiff-base ligands with the outer O2O2 moieties, and the Zn2+ Schiff-base complexes, as the suitable chromophores, could effectively sensitize of the NIR luminescence of the Ln3+ ions. On the one hand, the use of different counter-anions plays a key role on the structural types of the heterometallic complexes. For example, NO3- anion could coordinate with the Ln3+ ion and/or occupy the axial position of the Zn2+ ion, resulting in the formation of common

3

hetero-binuclear ZnLn complexes [10]. As to Cl- or OAc- anion with bridging function, Zn2Ln [11] or Zn2Ln2-arrayed complexes [12] are observed. By contrast, the use of mixed anions, especially oxygen-enriched mixed anions (OAc-/NO3- [13]), usually endows the simple ZnLn complexes with OAc--bridged linkage between. On the other hand, discrete Zn2Ln2 [14] or Zn4Ln2 [15] complexes and 1D [16] or 2D [17] coordination polymers in the presence of ancillary ligands can also be constructed. Nevertheless, in both heterometallic systems, the relatively “soft” Lewis acid 3d Zn2+ ion selectively lies in the cis-N2O2 core of the ligand and the “hard” Lewis acid 4f Ln3+ ion necessarily occupies the outer O2O2 moiety. As a matter of fact, it is well known that the coordination of Ln3+ ion in the cis-N2O2 core of the Salen-type Schiff-base ligands is common as shown polynuclear [18] or polymeric Ln3+ Salen complexes [19]. To some extent, it makes the self-assembly of 3d and 4f mixed metal complexes from the Salen-type Schiff-base ligands with the outer O2O2 moieties more complicated, which stimulates us further exploration on the new heterometallic complexes with both coordination modes of Ln3+ ions in the cis-N2O2 core and the outer O2O2 cavity. Herein, with the [Zn(L)(MeCN)]

from

the

typical

Salen-type

Schiff-base ligand

H2L

(H2L

=

N,N’-bis(3-methoxy-salicylidene)cyclohexane-1,2-diamine) as the precursor, two series of mixed anions (Cl-/N3-)-induced Zn2Ln complexes [Zn2(L)2 (MeOH)ClLn(N3)]·Cl (Ln = La, 1; Ln = Nd, 2; Ln = Yb, 3; Ln = Er, 4 or Ln = Gd, 5) and Zn2Ln3 complexes [Zn2(L)3Cl2(µ2-OH)(µ3-OH)2 Ln3(N3)2] (Ln = La, 6; Ln = Nd, 7; Ln = Yb, 8; Ln = Er, 9 or Ln = Gd, 10) are obtained, respectively. Differently from the Zn2Ln-arrayed complexes 1-5 with one Ln3+ ion in the two outer O2O2 moieties, the specialty of Ln3+ ions in both the cis-N2O2 core and the outer O2 O2 moiety endows the novel heterometallic complexes for 6-10. The

4

self-assembly mechanism on the same mixed anions-induced Zn2 Ln or Zn2Ln3 complexes and the comparison on their photophysical properties are also discussed.

2. Experimental Section 2.1 Materials and Methods All chemicals were commercial products of reagent grade and were used without further purification. Elemental analyses were performed on a Perkin-Elmer 240C elemental analyzer. Infrared spectra were recorded on a Nicolet Nagna-IR 550 spectrophotometer in the region 4000 - 400 cm-1 using KBr pellets. 1H NMR spectra were recorded on a JEOL EX270 spectrometer with SiMe4 as internal standard in CD3CN at room temperature. ESI-MS was performed on a Finnigan LCQDECA XP HPLC-MSn mass spectrometer with a mass to charge (m/z) range of 4000 using a standard electrospray ion source and CH3CN as solvent. Electronic absorption spectra in the UV/Vis region were recorded with a Cary 300 UV spectrophotometer, and steady-state visible fluorescence, PL excitation spectra on a Photon Technology International (PTI) Alphascan spectrofluorometer and visible decay spectra on a pico-N2 laser system (PTI Time Master). The quantum yield of the visible luminescence for each sample was determined by the relative comparison procedure, using a reference of a known quantum yield (quinine sulfate in dilute H2SO4 solution, Фem = 0.546). The Фem values were calculated as φem = φr (Br/Bs)(ns/nr)2 (Ds/Dr), in which the subscript s and r refer to the sample and the reference standard solution, respectively, n is the refractive index of the solvent, D is the integrated intensity, and B is the excitation intensity. Values of B were calculated as B = 1 - 10-AL, where A is the absorbance at the excitation wavelength and L is

5

the optical length (L = 1 cm) in all cases. The refractive indices of the solvents at room temperature were taken from standard sources, and errors for the φem values (±1%) were estimated. NIR emission and excitation in solution were recorded by PTI QM4 spectrofluorometer with a PTI QM4 Near-Infrared InGaAs detector.

2.2 Synthesis 2.2.1 Synthesis of the Salen-type Schiff-base ligand H2L (H2L =N,N’-bis(3-methoxy-salicylidene)cyclohexane-1,2-diamine ) The Salen-type Schiff-base ligand H2L was prepared from the condensation of the racemic 1,2-diaminocyclohexane (6.0 ml, 50 mmol) and o-vanillin (15.0 g, 100 mmol) in a molar ratio of 1:2 according to the typical procedure from the literature [19]. Yield: 13.6 g, 71%. Calc. for C22H26N2O4 : C, 69.09; H, 6.85; N, 7.32%; found: C, 69.01; H, 6.94; N, 7.25%. IR (KBr, cm-1): 3455 (b), 3058 (w), 2933 (w), 2862 (w), 2597 (w), 1619 (s), 1588 (w), 1470 (s), 1418 (m), 1345 (w), 1251 (vs), 1196 (w), 1168 (w), 1144 (w), 1085 (m), 1036 (w), 984 (m), 953 (w), 894 (w), 849 (w), 776 (w), 731 (m), 668 (w), 616 (w), 595 (w), 568 (w), 516 (w), 467 (w), 422 (w). 1H NMR (400 MHz, CD3CN): δ (ppm) 13.84 (s, 2H, -OH), 8.24 (s, 2H, -CH=N), 6.85 (d, 2H, -Ph), 6.78 (d, 2H, -Ph), 6.72 (t, 2H, -Ph), 3.86 (s, 6H, -OMe), 3.32 (m, 2H, -Ch), 1.92 (m, 4H, -Ch), 1.58 (m, 4H, -Ch).

2.2.2 Syntheses of precursor [Zn(L)(MeCN)] To a stirred solution of H2L (0.765 g, 2 mmol) in absolute MeCN (10 ml), solid Zn(OAc)2·2H2O (0.440 g, 2 mmol) was added, and the resultant mixture was heated under

6

reflux for 5 h. After cooling to room temperature, the clear yellow solution was filtered and solvent from the filtrate was allowed to evaporate slowly at room temperature. The yellow microcrystalline product of [Zn(L)(MeCN)] was isolated by filtration after several days. Yield: 0.430 g, 51%. Calc. for C24H27N3O4: C, 68.39; H, 6.46; N, 9.97%; found: C, 68.27; H, 6.74; N, 9.91%. IR (KBr, cm-1): 3053 (w), 2932 (w), 2845 (w), 2261 (w), 1636 (vs), 1545 (w), 1456 (s), 1395 (w), 1325 (m), 1231 (s), 1167 (w), 1084 (m), 1024 (w), 970 (w), 922 (w), 856 (w), 795 (w), 735 (m), 662 (w), 605 (w), 550 (w), 494 (w), 455 (w). 1H NMR (400 MHz, CD3CN): δ (ppm) 8.41 (s, 2H, -CH=N), 6.80 (d, 2H, -Ph), 6.77 (d, 2H, -Ph), 6.34 (t, 2H, -Ph), 3.71 (s, 6H, -OMe), 2.04 (m, 2H, -Ch), 1.52 (m, 4H, -Ch), 1.41 (m, 4H, -Ch).

2.2.3 Synthesis of complexes [Zn2(L)2(MeOH)ClLn(N3)]·Cl (Ln = La, 1; Ln = Nd, 2; Ln = Yb, 3; Ln = Er, 4 or Ln = Gd, 5) To a stirred solution of precursor [Zn(L)(MeCN)] (127 mg, 0.3 mmol) in absolute MeCN (10 ml), a solution of LnCl3 ·6H2O (0.3 mmol, Ln = La, 106 mg; Ln = Nd, 108 mg; Ln = Yb, 116 mg; Ln = Er, 115 mg or Ln = Gd, 112 mg) in absolute MeOH was added, and the mixture was continuously stirred overnight at room temperature. Solid NaN3 (59 mg, 0.9 mmol) was then added and the resultant final mixture was stirred at room temperature for 2 h. The respective pale yellow clear solution was filtered, and diethyl ether was allowed to diffuse slowly into the respective filtrate at room temperature, and then pale yellow microcrystallines 1-5 were obtained in about three weeks, respectively. For 1: Yield: 0.118 g, 61%. Calc. for C45H52N7O9Cl2Zn2La: C, 45.98; H, 4.46; N, 8.34%; found: C, 45.93; H, 4.62; N, 8.28%. IR (KBr, cm-1): 3126 (w), 2352 (w), 2061 (m), 1638 (s),

7

1472 (w), 1400 (vs), 1283 (w), 1241 (w), 1224 (m), 1175 (w), 1072 (s), 991 (w), 954 (m), 861 (w), 820 (w), 789 (w), 739 (m), 672 (w), 613 (w), 540 (w), 519 (w), 449 (w), 436 (w). 1H NMR (400 MHz, CD3CN): δ (ppm) 13.12 (s, 1H, -OH), 8.54 (s, 4H, -CH=N), 6.91 (d, 4H, -Ph), 6.80 (d, 4H, -Ph), 6.36 (t, 4H, -Ph), 3.71 (s, 12H, -OMe), 2.94 (m, 4H, -Ch), 2.05 (s, 3H, -CH3), 1.63 (m, 8H, -Ch), 1.51 (m, 8H, -Ch). ESI-MS (MeCN) m/z: 1140.07 ([M-Cl]+, 100%); 1176.53 ([M+H]+, 17%). For 2: Yield: 0.112 g, 63%. Calc. for C45H52 N7O9Cl2Zn2Nd: C, 45.77; H, 4.44; N, 8.30%; found: C, 45.68; H, 4.55; N, 8.23%. IR (KBr, cm-1): 3129 (w), 2362 (w), 2064 (m), 1635 (s), 1473 (w), 1401 (vs), 1278 (w), 1247 (w), 1222 (m), 1173 (w), 1074 (s), 993 (w), 952 (m), 865 (w), 824 (w), 784 (w), 737 (m), 669 (w), 617 (w), 541 (w), 517 (w), 447 (w), 431 (w). ESI-MS (MeCN) m/z: 1145.40 (100%, [M-Cl]+); 1181.86 (21%, [M+H]+). For 3: Yield: 0.105 g, 58%. Calc. for C45H52N7 O9Cl2Zn2Yb: C, 44.68; H, 4.33; N, 8.11%; found: C, 44.59; H, 4.37; N, 8.08%. IR (KBr, cm-1): 3123 (w), 2428 (w), 2361 (w), 2063 (m), 1633 (s), 1472 (w), 1399 (vs), 1283 (w), 1243 (w), 1223 (m), 1170 (w), 1082 (s), 991 (w), 961 (m), 859 (w), 832 (w), 786 (w), 743 (m), 665 (w), 618 (w), 542 (w), 516 (w), 473 (w), 458 (w). 440 (w). ESI-MS (MeCN) m/z: 1174.20 ([M-Cl]+, 100%); 1210.66 ([M+H]+, 14%). For 4: Yield: 0.103 g, 57%. Calc. for C45H52N7O9Cl2Zn2Er: C, 44.90; H, 4.35; N, 8.14%; found: C, 44.85; H, 4.40; N, 8.02%. IR (KBr, cm-1): 3129 (w), 2427 (w), 2362 (w), 2062 (m), 1635 (s), 1471 (w), 1400 (vs), 1281 (w), 1241 (w), 1221 (m), 1174 (w), 1080 (s), 991 (w), 959 (m), 858 (w), 830 (w), 789 (w), 742 (m), 664 (w), 617 (w), 540 (w), 518 (w), 472 (w), 454 (w). 442 (w). ESI-MS (MeCN) m/z: 1168.42 ([M-Cl]+, 100%); 1204.88 ([M+H]+, 15%). For 5: Yield: 0.115 g, 64%. Calc. for C45H52 N7O9Cl2Zn2Gd: C, 45.27; H, 4.39; N, 8.21%;

8

found: C, 45.15; H, 4.47; N, 8.16%. IR (KBr, cm-1): 3137 (w), 2421 (w), 2366 (w), 2066 (m), 1637 (s), 1468 (w), 1402 (vs), 1306 (w), 1278 (w), 1243 (w), 1222 (m), 1170 (w), 1080 (s), 990 (w), 957 (m), 850 (w), 830 (w), 783 (w), 743 (m), 664 (w), 615 (w), 545 (w), 520 (w), 475 (w), 461 (w). 432 (w). ESI-MS (MeCN) m/z: 1158.41 ([M-Cl]+, 100%); 1194.87 ([M+H]+, 11%).

2.2.4 Synthesis of complexes [Zn2(L)3Cl2(µ2-OH)(µ3-OH)2Ln3(N3)2](Ln = La, 6; Ln = Nd, 7; Ln = Yb, 8; Ln = Er, 9 or Ln = Gd, 10) To a stirred solution of precursor [Zn(L)(MeCN)] (127 mg, 0.3 mmol) in absolute MeCN (10 ml), a solution of LnCl3 ·6H2O (0.3 mmol, Ln = La, 106 mg; Ln = Nd, 108 mg; Ln = Yb, 116 mg; Ln = Er, 115 mg or Ln = Gd, 112 mg) in absolute MeOH was added, and the mixture was refluxed for about 2 h. After cooling to room temperature, solid NaN3 (59 mg, 0.9 mmol) was then added and the resultant final mixture was stirred at room temperature for another 2 h. The respective pale yellow clear solution was filtered, and diethyl ether was allowed to diffuse slowly into the respective filtrate at room temperature, and then pale yellow microcrystallines 6-10 were obtained in about several weeks, respectively. For 6: Yield: 0.085 g, 45%. Calc. for C66H75 N12O15Cl2 Zn2La3: C, 41.84; H, 3.99; N, 8.87%; found: C, 41.72; H, 4.03; N, 8.82%. IR (KBr, cm-1): 3058 (w), 2940 (m), 2852 (w), 2065 (m), 1658 (vs), 1551 (w), 1498 (m), 1475 (s), 1381 (m), 1280 (m), 1222 (m), 1169 (w), 1082 (m), 1022 (w), 959 (m), 912 (w), 855 (m), 781 (w), 745 (s), 662 (m), 618 (w), 557 (w), 509 (w). 1H NMR (400 MHz, CD3CN): δ (ppm) 14.07 (s, 2H, -OH-), 13.32 (s, 1H, -OH-), 8.52 (s, 6H, -CH=N), 6.93 (d, 6H, -Ph), 6.79 (d, 6H, -Ph), 6.42 (t, 6H, -Ph), 3.79 (s, 18H,

9

-OMe), 2.14 (m, 6H, -Ch), 1.58 (m, 12H, -Ch), 1.52 (m, 12H, -Ch). ESI-MS (CH3CN) m/z: 1852.76 ([M-N3]+, 100%); 1895.78 ([M+H]+, 20%). For 7: Yield: 0.082 g, 43%. Calc. for C66H75N12O15Cl2Zn2Nd3: C, 41.49; H, 3.96; N, 8.80%; found: C, 41.46; H, 4.02; N, 8.71%. IR (KBr, cm-1): 3063 (w), 2934 (m), 2858 (w), 2064 (m), 1655 (vs), 1551 (w), 1503 (m), 1460 (s), 1387 (m), 1288 (m), 1223 (m), 1167 (w), 1076 (m), 1022 (w), 957 (m), 908 (w), 853 (m), 789 (w), 745 (s), 671 (m), 615 (w), 554 (w). ESI-MS (MeCN) m/z: 1868.76 ([M-N3]+, 100%); 1911.79 ([M+H]+, 17%). For 8: Yield: 0.102 g, 51%. Calc. for C66H75N12O15Cl2Zn2Yb3: C, 39.69; H, 3.79; N, 8.42%; found: C, 39.61; H, 3.85; N, 8.37%. IR (KBr, cm-1): 3063 (w), 2934 (m), 2858 (w), 2068 (m), 1658 (vs), 1557 (w), 1501 (m), 1470 (s), 1387 (m), 1288 (m), 1227 (m), 1169 (w), 1084 (m), 1022 (w), 961 (m), 908 (w), 856 (m), 789 (w), 746 (s), 673 (m), 619 (w), 555 (w), 505(w). ESI-MS (MeCN) m/z: 1955.16 ([M-N3 ]+, 100%); 1989.19 ([M+H]+, 14%). For 9: Yield: 0.099 g, 50%. Calc. for C66H75N12O15Cl2Zn2Er3: C, 40.04; H, 3.82; N, 8.49%; found: C, 39.97; H, 3.85; N, 8.46%. IR (KBr, cm-1): 3060 (w), 2938 (m), 2859 (w), 2067 (m), 1653 (vs), 1558 (w), 1504 (m), 1471 (s), 1389 (m), 1283 (m), 1226 (m), 1168 (w), 1080 (m), 1020 (w), 958 (m), 914 (w), 853 (m), 785 (w), 742 (s), 664 (m), 615 (w), 558 (w), 507 (w). ESI-MS (MeCN) m/z: 1937.82 ([M-N3]+, 100%); 1980.85 ([M+H]+, 12%). For 10: Yield: 0.094 g, 48%. Calc. for C66H75N12O15Cl2Zn2Gd3: C, 40.66; H, 3.88; N, 8.62%; found: C, 40.53; H, 3.93; N, 8.56%. IR (KBr, cm-1): 3065 (w), 2936 (m), 2858 (w), 2066 (m), 1652 (vs), 1555 (w), 1502 (m), 1464 (s), 1389 (m), 1288 (m), 1223 (m), 1169 (w), 1078 (m), 1022 (w), 959 (m), 912 (w), 854 (m), 789 (w), 745 (s), 671 (m), 615 (w), 555 (w), 509 (w). ESI-MS (MeCN) m/z: 1909.79 ([M-N3]+, 100%); 1950.82 ([M+H]+, 15%).

10

2.3 X-ray crystallography Single crystals of 2·3H2O and 9·2H2 O of suitable dimensions were mounted onto thin glass fibers. All the intensity data were collected on a Bruker SMART CCD diffractometer (Mo-Kα radiation and λ = 0.71073 Å) in Φ and ω scan modes. Structures were solved by Direct methods followed by difference Fourier syntheses, and then refined by full-matrix least-squares techniques against F2 using SHELXTL [20]. All other non-hydrogen atoms were refined with anisotropic thermal parameters. Absorption corrections were applied using SADABS [21]. All hydrogen atoms were placed in calculated positions and refined isotropically using a riding model. Crystallographic data and refinement parameters for the complexes are presented in Table 1. Relevant atomic distances and bond angles are collected in Table 2. CCDC reference numbers 979121 (for 2⋅3H2O) and 979122 (for 9⋅2H2 O).

3. Results and discussion 3.1 Synthesis and characterization As shown in Scheme 1, reaction of equimolar amount of the Salen-type Schiff-base ligand H2L and Zn(OAc)2·2H2O in absolute MeCN, afforded the precursor [Zn(L)(MeCN)] in a yield of 51%. Further through reaction of the precursor with LnCl3·6H2O (Ln = La, Nd, Yb, Er or Gd) and NaN3 in mixed solvents (MeOH-MeCN) with a molar ratio of 1:1:3 at room temperature, series of hetero-trinuclear Zn2Ln complexes [Zn2(L)2(MeOH)ClLn(N3)]·Cl (Ln = La, 1; Ln = Nd, 2; Ln = Yb, 3; Ln = Er, 4 or Ln = Gd, 5) were obtained, respectively. However, when the reaction was dealt with reflux under the same condition, another series of

11

hetero-pentanuclear Zn2Ln3 [Zn2(L)3Cl2(µ2-OH)(µ3 -OH)2Ln3(N3)2] (Ln = La, 6; Ln = Nd, 7; Ln = Yb, 8; Ln = Er, 9 or Ln = Gd, 10) were always obtained, respectively. The differences of composition and structure (vida infra) on the two series of Zn2Ln-arrayed and Zn2Ln3-arrayed complexes should be resulted from the variation of the reaction temperature. [Scheme 1 inserted here] The precursor [Zn(L)(MeCN)] and two series of Zn2Ln-arrayed complexes 1-5 and Zn2Ln3-arrayed complexes 6-10 were well characterized by EA, FT-IR, 1H NMR and ESI-MS. In the FT-IR spectra, the characteristic strong absorptions of the ν(C=N) vibrations at 1636 cm-1 for the precursor [Zn(L)(MeCN)], 1633-1638 cm-1 for complexes 1-5 or 1652-1658 cm-1 for complexes 6-10, respectively, are distinctively blue-shifted by the range of 17 cm-1 , 14-19 cm-1 or 33-39 cm-1 relative to that (1619 cm-1) of the free ligand H2L upon the coordination of the metal ions. For complexes 1-5 and 6-10, an additional characteristic absorptions at 2061-2068 cm-1 should be attributed to the νas vibrations of coordinated N3- anion. As to the room temerature 1H NMR spectra of complexes Zn2La (1) and Zn2La3 (6), besides the disappearance of the typically intramolecular resonance-assisted hydrogen bonded (RAHB) [22] O-H···N proton resonances of the free Salen-type Schiff-base ligand H2L, slightly spread shifts (δ from 8.54 to 1.51 ppm for 1 and 8.52 to 1.52 ppm for 6) of the proton resonances of the coordinated ligands relative to that (δ from 8.24 to 1.58 ppm) of the free ligand are observed, respectively. The ESI-MS spectra of the two series of complexes 1-5 and 6-10 in MeCN display the respective similar patterns and exhibit the strong mass peak at m/z 1140.07 (1), 1145.40 (2), 1174.20 (3), 1168.42 (4) or 1158.41 (5) assigned to the major species [Zn2(L)2(MeOH)ClLn(N3)]+ of complexes 1-5 and the strong mass peak at m/z 1852.76 (6),

12

1868.76 (7), 1955.16 (8), 1937.82 (9) or 1909.79 (10) corresponded to the major species {[Zn2(L)3Cl2(µ2-OH)(µ3-OH)2Ln3(N3 )]}+ (Ln = La, Nd, Yb, Er or Gd) of complexes 6-10, respectively. This result further indicates that the respective discrete Zn2 Ln or Zn2Ln3 unit retains in the respective dilute MeCN solution. The solid state structure of 2·3H2O or 9·2H2O as the respective representative of complexes 1-5 and 6-10 was determined by X-ray single-crystal diffraction analysis. Crystallographic data for the two complexes are presented in Table 1, and selected bond lengths and angles are given in Table 2, respectively. Complex 2·3H2O crystallizes in the monoclinic system with the space group of P21/n, where the smallest repeated unit is composed of one cation [Zn2(L)2(MeOH)ClNd(N3)]+, one free Cl- anion and three solvates H2O. As shown in Figure 1, for the cationic [Zn2(L)2 (MeOH)ClNd(N3)]+ part, the two outer O2O2 moieties of the two [Zn(L)] components coordinate with one Nd3+ ion, resulting in the formation of a hetero-trinuclear Zn2Nd-arrayed host structure. Each of the two Zn2+ ion (Zn1 or Zn2) is five-coordinated and adopts a distinctively distorted square pyramidal geometry, in which the similar inner cis-N2O2 core from the respective (L)2- ligand comprises the base plane, while one coordinated Cl- anion or one O atom of coordinated MeOH occupies at the apical position, respectively. The Nd3+ ion (Nd1) is the nine-coordinate, and in addition to the eight O atoms from two outer O2O2 moieties of the two [Zn(L)] components, it completes its coordination environment with one N atom from the coordinated N3- anion. The two slightly different Zn1···Nd distances (3.525(2)-3.639(3) Å) bridged by two µ-O phenoxide atoms (O2 and O3 or O6 and O7) should be due to the different anions-induced distortion of the two flexible Salen-type Schiff-base ligands. The other free counter-anion Cl- and solvates H2O of

13

complex 2·3H2O are not bound to the framework, and they exhibit no observed interaction with the host structure. [Figure 1 inserted here] 9·2H2O crystallizes in the monoclinic system with the space group of P21/c, where one neutral [Zn2(L)3 Cl2(µ2-OH)(µ3-OH)2Er3(N3 )2] molecule and two solvates H2O comprise the smallest repeated unit. As shown in Figure 2, two [Zn(L)] parts and one [Er(L)]+ part with metal ions in each of the inner cis-N2 O2 core of the three ligands are bridged by two µ3-OHgroups and one µ2-OH- group with other two Er3+ ions (Er2 and Er3), resulting in the formation of a novel Zn2Er3-arrayed host structure. Each Zn2+ ion (Zn1 or Zn2) has a five-coordinate environment and adopts the typically distorted square pyramidal geometry, while different anions (N3- and Cl-) occupy the axial positions, respectively. The unique inner Er3+ ion (Er1) is eight-coordinate and bound by two O atoms (O13 and O14) of two coordinated µ3-OH- groups, one N3- and one Cl- besides four atoms (N5, N6, O10 and O11) from the cis-N2O2 core of one ligand. However, one of the outer Er3+ ions (Er2) is nine-coordinate: in addition to six O atoms from two O2O2 moities of two ligands, it saturates its coordination environment with two O atoms (O13 and O14) from two coordinated µ3-OHgroups and one O atom (O15) from the coordinated µ2-OH- group. As to the other outer Er3+ ion (Er3), it is also eight-coordinate, in which just five O atoms from two O2O2 moities of two ligands, two O atoms (O13 and O14) from two coordinated µ3-OH- groups and one O atom (O15) from the coordinated µ2-OH- group surround. The Zn1···Er2 distance (3.433(3) Å) bridged by two µ-O phenoxide atoms (O2 and O3) is slightly shorter than that (3.472(3) Å) of between Zn2 and Er3 bridged by O6 and O7 atoms, and the Er2···Er3 distance (3.4631(4) Å)

14

connected by µ2-OH- group is also slightly shorter than those (3.5395(14)-3.5653(14) Å) of the Er1···Er2 and Er1···Er3 distances bridged by µ3-OH- groups. The two solvate H2O molecules of 9·2H2O are not bound to the framework, and they exhibit no observed interaction with the host structure. [Figure 2 inserted here] It is of interest to explore the self-assembly mechanism of the two series of Zn2Ln-arrayed and Zn2Ln3-arrayed complexes, where the same raw materials and reaction conditions except reaction temperature are used. At room temperature, the borderline Lewis base Cl- or MeOH could bind the medium-hard acidic Zn2+ ion at the apical position and the anion N3- selectively bind the hard acidc Nd3+ ion probably due to the sp2 hybrids of two terminal N atoms. On the reaction condition of reflux especially in alcohol-containing solution, the strong heat exacerbates demetalation of partial precursors [Zn(L)(MeCN). The demetalation factually results in the selective exchange of Zn2+ centers for the hard acidic Ln3+ ions in addition to other transition metal ions [23], and leads to the formation of the novel heterometallic Zn2Ln3-arrayed complexes 6-10. For Zn2Ln-arrayed complexes 1-5, the coordination modes of Zn2+ ions at the inner cis-N2O2 cores and Ln3+ ions at the outer O2 O2 moieties of the Salen-type Schiff-base ligands are common and similar to those of the reported discrete ZnLn [10, 13], Zn2Ln [11], Zn2Ln2 [12, 14] and Zn2 Ln4 [15] or polymeric [16-17] complexes. As to the Zn2 Er3-arrayed structure in complexes 6-10, the combination of one inner and two outer Ln3+ ions is distinctively different from that of those complexes [10-17] with Ln3+ ions just at the outer O2O2 moieties of the Salen-type Schiff-base ligands despite the same coordination of Zn2+ ions at the inner cis-N2O2 cores. Furthermore, although

15

the Zn2Er3 -arrayed host induced by mixed anions is also found in the reported magnetic N3--induced complex [Zn2Tb3(µ3-OH)2(N3)5(Salen)3] [24], both should be due to demetalation while not the use of Et3N as the literature [24].

3.2 Photophysical properties of complexes 2-5 and 7-10 The photophysical properties of ligand H2L, precursor [Zn(L)(MeCN)] and two series of complexes 2-5 and 7-10 have been examined in dilute MeCN at room temperature or 77 K, and summarized in Table 3 and Figures 3-7. As shown in Figure 3, the similar ligand-centered solution absorption spectra of 236, 276 and 362 nm for the precursor, and 228-229, 258-261 and 344-346 nm for complexes 2-5 in the UV-visible region are observed, respectively. Both are red-shifted up coordination of metal ions compared to that (220, 258 and 327 nm) of the free Salen-type Schiff-base ligand H2L. Compared with the precursor, the lowest energy absorptions of complexes 2-5 are blue-shifted by 17-19 nm upon further coordination of Ln3+ ions, and the molar absorption coefficients of complexes 2-5 in all the lowest energy bands are about two orders of magnitude larger than that of the precursor due to the involvement of two energy donors. For complexes 2-4, the similar weak visible emission (λem = 464 nm and τ < 1 ns) with low quantum yields (Φem < 10-5) are observed. In addition to the residual weak visible emissions, as shown in Figure 4, photo-excitation of the antennae at the range of 220-420 nm (λex = 350 nm for 2 or λex = 354 nm for 3) gives rise to the strong characteristic emissions of the Nd3+ ion (4F3/2 → 4IJ/2, J = 9, 11, 13) or the Yb3+ ion (2F5/2 → 2 F7/2) in the NIR region, respectively. For complex 2, the emissions at 890, 1083 and 1330 nm can be attributed to 4F3/2 → 4I9/2, 4F3/2 → 4 I11/2 and 4F3/2 → 4I13/2 transitions of the Nd3+ ion, respectively, and the

16

emission at 978 nm can be attributed to 2F5/2 → 2F7/2 transition of the Yb3+ ion for complex 3. However, unlike that for complex 2 or 3, the characteristic NIR emission of the Er3+ ion for complex 4 cannot be observed. The free ligand, the precursor or complex 5 also does not exhibit the NIR emission under the same condition, and just displays the strong luminescence (λem = 480 nm, τ = 1.16 ns and Φem = 1.1% for H2 L, λem = 494 nm, τ = 1.56 ns and Φem = 1.56% for the precursor or λem = 463 nm, τ = 0.71 ns and Φem = 0.046% for 5) of the typical Salen-type Schiff-base ligand in the visible range, as shown in Figure 5. The excitation spectra of complexes 2-3, monitored at the respective NIR emission peak (1083 nm for 2 or 978 nm for 3), are similar to those monitored at their respective residual visible emission peak, which clearly demonstrates that both the NIR and visible emissions for complexes 2-3 originate from the same π-π* transitions of the ligand H2L, and the energy transfer from the antenna to the Ln3+ ion takes place efficiently [25]. [Figures 3-5 inserted here] As a reference compound, complex 5 endows the further study of the chromophore luminescence in the absence of energy transfer, because the Gd3+ ion has no energy levels below 32000 cm-1, and thus cannot accept any energy from the excited state of the chromophores [26]. In dilute MeCN solution at 77 K, compared with that (λem = 463 nm, τ = 0.71 ns and Φem = 0.046%) at room temperature on the same condition, complex 5 exhibits the strengthened luminescence, which shows the higher luminescent intensity (λem = 456 nm and 478 nm) and the distinctively longer luminescence lifetimes (1.97 ns and 6.96 ms). This result demonstrates that the sensitization of the NIR luminescence for complexes 2-3 should arise from both the 1LC (21930 cm-1) and the 3LC (20921 cm-1) excited state of the

17

Schiff-base ligand H2L at low temperature [27]. If the antennae luminescence lifetime of complex 5 is to represent the excited-state lifetime in the absence of the energy transfer, the energy transfer rate (kET) in the complexes 2-4 can thus be calculated from kET = 1/τq – 1/τu [28], where τq is the residual lifetime of the luminescent emission undergoing quenching by the respective Ln3+ ion, and τu is the unquenched lifetime in the reference complex 5, so the energy transfer rates for the Ln3+ ions in complexes 2-4 may all be estimated to be above 5×108 s-1, which could well imply the reason to the effective energy transfer for complexes 2-4. Furthermore, from the viewpoint of the energy level match, in spite of the effective energy transfer also taking place in complex 4, the larger energy gap between the energy-donating 3LC level (20921 cm-1) and the emitting level (4 I13/2, 6460 cm-1) of Er3+ ion than those (∆E = 9234-10225 cm-1) of complexes 2-3 results in the great non-radiative energy loss during the energy transfer, which should be the reason to the unobservable luminescence in the range of 800-1800 nm for complex 4 [29]. Moreover, for complexes 2-3, the respective NIR luminescent decay curves obtained from time-resolved luminescent experiments can be fitted mono-exponentially with time constant of microseconds (1.68 µs for 2 at 1083 nm and 15.36 µs for 3 at 978 nm), and the intrinsic quantum yield ФLn (0.67% for 2 or 0.88% for 3) of the Ln3+ emission may be estimated by ФLn = τobs/τ0, where τobs is the observed emission lifetime and τ0 is the “natural lifetime”, viz 0.25 ms and 2.0 ms for the Nd3+ and Yb3+ ions, respectively [30]. As to the relatively higher quantum efficiency of 3 (0.88%) than that of 2 (0.67%), although the slightly larger energy gap (∆E = 10225 cm-1) of Yb3+ ion in complex 3 than that (∆E = 9234 cm-1) of the Nd3+ ion in complex 2, it is should be due to the quantities of accepting levels of the Nd3+ ion while only one for the Yb3+ ion [31].

18

The change of reaction temperature results in structure changes from Zn2Ln to Zn2Ln3, and the different photophysical properties of complexes 7-10 are presented in Table 3 and Figures 5-7. As shown in Figure 6, besides the simialr red-shifted ligand-centered solution absorption spectra of 236-238, 275-277 and 351-353 nm for complexes 7-10 in the UV-visible region than that (220, 258 and 327 nm) of the free Salen-type Schiff-base ligand H2L, the lowest energy absorptions of complexes 7-10 are blue-shifted by 9-11 nm compared to the precuosor upon further coordination of Ln3+ ions, and the molar absorption coefficients in all the lowest energy bands are about three orders of magnitude larger than that of the precursor due to the involvement of three energy donors. For complexes 7-10, besides the similar residual visible emissions (λem = 475 nm, τ < 1 ns and Φem < 10-5), photo excitation (λex = 375 nm) of the antennae at the range of 275-500 nm, as shown in Figure 7, also gives rise to the characteristic strong emissions of the Nd3+ ion (4F3/2 → 4IJ/2, J = 9, 11 and 13; λem = 888, 1074 and 1342 nm), the Yb3+ ion (2 F5/2 →2F7/2; λem = 980 nm), and weak emission of the Er3+ ion (4I13/2 → 4I15/2) in the NIR region, respectively. As to the Zn2Gd3 10, it also just has the weakened luminescence (λem = 474 nm, τ = 0.56 ns and Φem = 0.021%) of the Salen-type Schiff-base ligand H2L in the visible region at room temperature, as shown in Figure 5. The fact of the similar excitation spectrum (λex = 375 nm) for each of complexes 7-9 monitored at the respective NIR or visible emission peak also shows that both the visible and NIR emissions of complexes 7-9 should originate from the same π-π* transitions of the ligand H2L [25]. However, for complexes 7 and 8, the respective luminescent decay curves obtained from time-resolved luminescent experiments can be fitted bi-exponentially with the time constants of microseconds (1.1 µs (73%) and 1.0 µs (27%) for 7 at 1074 nm or 10.8 µs (65%) and 9.7

19

µs (35%) for 8 at 980 nm), and the avarage instrinsic quantum yield ΦLn (0.43% for 7 or 0.52% for 8) may be estimated. This result indicates the presence of two emitting centers for both 7 and 8 in dilute solution in agreement with one inner and two outer coordination environments of the three Ln3+ ions. Due to the rather week NIR emission of complex 9, the instrinsic quantum yield ΦLn of Er3+ ion could not been estimated. Simialr to complex 5, in the dilute MeCN solution at 77 K, complex 10 also displays both the stronger antenna fluorescence (λem = 462 nm and τ = 1.20 ns) and the strong antenna phosphorescence (λem = 497 nm and τ = 4.21 ms), also showing that the sensitization of the NIR luminescence for complexes 7-9 should arise from both the 1LC and 3LC excited states of the Salen-type Schiff-base ligand H2L at 77 K [27]. It is of special interest to compare the photophysical properties of the two series of Zn2Ln-arrayed complexes 2-5 and Zn2Ln-arrayed complexes 7-10. Although the similar strong respective characteristic NIR emssion of Nd3+ or Yb3+ ion for 7-8 to that for 2-3 arised from both the 1LC and 3LC excited states of the Salen-type Schiff-base ligand H2L, the relatively lower NIR quantum efficiencies of 7 (0.43%) and 8 (0.52%) than those (0.67-0.88%) of complexes 2-3, which should be resulted from the luminescent quenching with the involvement of three OH- oscillators arround the three Ln3+ ion in complex 7 or 8 [9]. Moreover, similar to that of complex 4, the weak characteristic NIR emission of the Er3+ ion for complex 9 is observed further due to the larger energy gap (∆E = 13661 cm-1) between the energy-donating 3LC (20121 cm-1) and the emitting level (4I13/2, 6460 cm-1) of Er3+ ion [29]. As the reason to the higher intrinsic quantum yield ФLn (0.52%) of the Yb3+ emission for 8 than that (0.43%) of the Nd3+ emission for 7, the excited state of the Nd3+ ions in 7 is more

20

sensitive to luminescent quenching by the nearby three OH- oscillators besides the less opportunities of non-radiative migration from the single emitting transition (2F5/2 → 2F7/2) of the Yb3+ ion in 8 [9] besides the quantities of accepting levels of the Nd3+ ion [31], although the energy gap (∆E = 8864 cm-1) of the Nd3+ ion in 7 is smaller than that (∆E = 10259 cm-1) of Yb3+ ion in 8. [Figures 6-7 inserted here] 4. Conclusions In conclusion, two series of mixed anions-induced Zn2Ln-arrayed complexes [Zn2(L)2(MeOH)ClLn(N3)]·Cl (Ln = La, 1; Ln = Nd, 2; Ln = Yb, 3; Ln = Er, 4 or Ln = Gd, 5) and Zn2Ln3-arrayed complexes [Zn2(L)3Cl2(µ2-OH)(µ3-OH)2Ln3(N3 )2] (Ln = La, 6; Ln = Nd, 7; Ln = Yb, 8; Ln = Er, 9 or Ln = Gd, 10) are obtained from the self-assembly of the precursor [Zn(L)(MeCN)] with LnCl3·6H2O (Ln = La, Nd, Yb, Er or Gd) and NaN3 in alcohol-containing solutions at room temperature or under reflux, respectively. Especially, the formation of novel heterometallic Zn2Ln3-arrayed complexes 7-10 with the Ln3+ ions in both the inner cis-N2O2 core and the outer O2 O2 moieties of the ligands, should be resulted from the demetalation of partial precursors leads to the selective exchange of Zn2+ centers for the Ln3+ ions. The result of their photophysical properties shows that the characteristic near-infrared (NIR) luminescence of Nd3+ or Yb3+ ion has been sensitized from the excited state (both 1LC and 3LC) of the ligand H2 L, while relatively lower quantum yields for Zn2Ln3-arrayed complexes should be due to the luminescent quenching with the involvement of OH- oscillators arround the Ln3+ ions. The avoidance luminescent quenching with the involvement of OH- oscillators arround the Ln3+ ions for enhanced NIR luminescent

21

hetero-multinuclear complexes needs the further choice of other mixed anions in the future.

Acknowledgements This work is funded by the National Natural Science Foundation (21373160, 91222201, 21173165, 20871098), the Program for New Century Excellent Talents in University from the Ministry of Education of China (NCET-10-0936), the research fund for the Doctoral Program (20116101110003) of Higher Education, the Education Committee Foundation (11JK0588) the Science, Technology and Innovation Project (2012KTCQ01-37) of Shaanxi Province, Graduate Innovation and Creativity Fund (YZZ12038) of Northwest University, Hong Kong Research Grants Council (HKBU 202407 and FRG/06-07/II-16) in P. R. of China, the Robert A. Welch Foundation (Grant F-816), the Texas Higher Education Coordinating Board (ARP 003658-0010-2006) and the Petroleum Research Fund, administered by the American Chemical Society (47014-AC5).

Appendix A. Supplementary data The crystallographic data for complexes 2·3H2O and 9·2H2O have been deposited at the Cambridge Crystallographic Data Center, CCDC-979121-979122 (for 2·3H2O and 9·2H2O). The data can be obtained free of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html or from the Cambridge CB21EZ, UK.

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(b) W. X. Feng, Y. Zhang, Z. Zhang, X. Q. Lü, H. Liu, G. X. Shi, D. Zou, J. R. Song, D. D. Fan, W.-K. Wong, R. A. Jones, Anion-induced self-assembly of luminescent and magnetic homoleptic cyclic tetranuclear Ln4 (Salen)4 and Ln4(Salen)2 complexes (Ln = Nd, Yb, Er or Gd), Inorg. Chem. 51 (2012) 11377-11386. [19] X. P. Yang, R. A. Jones, J. H. Rivers, W.-K. Wong, Synthesis, structures, and photoluminescence of 1-D lanthanide coordination polymers, Dalton Trans. (2009) 10505-10510. [20] G. M. Sheldrick, SHELXL-97: Program for Crystal Structure Refinement, Göttingen, Germany, (1997). [21] G. M. Sheldrick, SADABS, University of Göttingen, (1996). [22] P. Gilli, V. Bertolasi, V. Ferratti, G. Gilli, Evidence of intramolecular N-H···O resonance-assisted hydrogen bonding in β-enaminones and related heterodynes. A combined crystal-structural, IR and NMR spectroscopic, and quantum-mechanical investigation, J. Am. Chem. Soc. 122 (2000) 10405-10417. [23] E. C. Escudero-Adán, J. Benet-Buchholz, A. W. Kleij, Expedient method for the transmetalation of Zn(II)-centered Salphen complexes, Inorg. Chem. 46 (2007) 7165-7267. [24] C. E. Burrow, T. J. Burchell, P.-H. Lin, F. Habib, W. Wernsdorfer, R. Clérac, M. Murugesu,

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[29] J.-C. G. Bünzli, S. V. Eliseeva, in Springer Series on Fluorescence, Vol. 7, Lanthanide Spectroscopy, Materials, and Bio-applications, ed. P. Hänninen and H. Härmä, Springer Verlag, Berlin, 2010, vol. 7, ch. 2. [30] M. J. Weber, Radiative and multiphonon relaxation of rare-ions in Y2O3, Phys. Rev. 171 (1968) 283-291. [31] T. Nishioka, K. Fukui, K. Matsumoto, in: K. A. Gschneidner, Jr, J.-C. G. Bünzli, V. K. Pecharsky (Eds.), Handbook on the Physics and Chemistry of Rare Earths, Elsevier Science B. V., Amsterdam, 2007, vol. 37, ch. 11.

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Table 1 Crystal data and refinement for 2·3H2O and 9·2H2O Compound

2·3H2 O

9·2H2O

Empirical formula

C45H58N7O12Cl2Zn2Nd

C 66H 79N 12O17Cl2Zn2Er3

Formula weight

1234.86

2015.83

Crystal system

Monoclinic

Monoclinic

Space group

P2(1)/n

P2(1)/c

A/Å

19.853(3)

16.6056(10)

b/Å

16.519(2)

21.2872(11)

c/Å

20.166(2)

22.7008(12)

α/˚

90

90

β/˚

94.169(2)

92.244(4)

90

90

γ/˚ 3

6596.0(14)

8018.3(8)

Z

4

4

ρ/g·cm-3

1.244

1.670

Crystal size/mm

0.33 × 0.28 × 0.24

0.36 × 0.30 × 0.25

µ(Mo-K α)/mm-1

1.629

3.830

Data/restraints/parameters

12832/0/622

6304/0/919

Quality-of-fit indicator

V/Å

1.049

1.112

No. Unique reflections

12832

6304

No. Observed reflections

34347

57178

Final R indices [I>2σ(I)]

R1 = 0.0678

R1 = 0.0595

W R2 = 0.2006

W R2

R1 = 0.1364

R1 = 0.0913

R indices (all data)

W R2

= 0.2532

29

W R2

= 0.1684 = 0.2044

Table 2 Interatomic distances (Å) and bond angles (˚) with esds for complexes 2·3H2O and 9·2H2O 2·3H2 O

9·2H2 O

Zn(1)-N(1)

2.045(8)

Zn(2)-N(3)

2.037(8)

Zn(1)-N(1)

2.050(20)

Zn(2)-N(3)

2.031(19)

Zn(1)-N(2)

2.080(7)

Zn(2)-N(4)

2.041(7)

Zn(1)-N(2)

2.033(19)

Zn(2)-N(4)

2.040(20)

Zn(1)-O(2)

2.067(5)

Zn(2)-O(6)

2.062(5)

Zn(1)-N(7)

2.000(20)

Zn(2)-Cl(1)

2.244(11)

Zn(1)-O(3)

2.005(6)

Zn(2)-O(7)

2.027(5)

Zn(1)-O(2)

2.042(14)

Zn(2)-O(6)

2.066(14)

Zn(1)-Cl(1)

2.289(4)

Zn(2)-O(9)

2.162(8)

Zn(1)-O(3)

2.064(14)

Zn(2)-O(7)

2.017(16)

Nd(1)-N(5)

2.404(9)

N(1)-Zn(1)-N(2)

80.5(3)

Er(1)-N(5)

2.460(20)

Er(2)-O(1)

2.618(15)

Nd(1)-O(1)

2.696(6)

N(1)-Zn(1)-O(2)

87.9(3)

Er(1)-N(6)

2.490(20)

Er(2)-O(2)

2.331(15)

Nd(1)-O(2)

2.425(6)

N(1)-Zn(1)-O(3)

141.4(3)

Er(1)-N(10)

2.350(20)

Er(2)-O(3)

2.371(14)

Nd(1)-O(3)

2.399(6)

N(1)-Zn(1)-Cl(1)

105.7(3)

Er(1)-Cl(2)

2.890(50)

Er(2)-O(4)

2.737(15)

Nd(1)-O(4)

2.731(6)

Er(1)-O(10)

2.318(15)

Er(2)-O(11)

2.361(13)

Nd(1)-O(5)

2.629(5)

N(3)-Zn(1)-N(4)

79.7(3)

Er(1)-O(11)

2.324(15)

Er(2)-O(12)

2.462(13)

Nd(1)-O(6)

2.399(5)

N(3)-Zn(1)-O(6)

88.4(3)

Er(1)-O(13)

2.311(13)

Er(2)-O(13)

2.383(14)

Nd(1)-O(7)

2.410(5)

N(3)-Zn(1)-O(7)

141.1(3)

Er(1)-O(14)

2.414(13)

Er(2)-O(14)

2.366(14)

Nd(1)-O(8)

2.645(5)

N(3)-Zn(1)-O(9)

105.9(4)

Er(2)-O(15)

2.242(14)

O(1)-Nd(1)-O(4)

146.63(15)

O(2)-Nd(1)-O(3)

63.53(19)

O(5)-Nd(1)-O(8)

152.84(19)

O(6)-Nd(1)-O(7)

64.77(17)

N(5)-Nd(1)-O(1)

144.9(2)

Er(3)-O(6)

2.259(16)

Er(3)-O(7)

2.316(13)

3.6393(11)

Zn(2) · ··Nd(1)

3.5254(10)

78.7(8)

Er(3)-O(8)

2.464(14)

N(1)-Zn(1)-N(7)

111.1(9)

Er(3)-O(9)

2.499(14)

N(1)-Zn(1)-O(2)

90.9(7)

N(1)-Zn(1)-O(3)

137.6(7)

Er(3)-O(10) Zn(1)· ··Nd(1)

N(1)-Zn(1)-N(2)

2.334(14)

Er(3)-O(13)

2.446(14)

Er(3)-O(14)

2.272(14)

N(3)-Zn(2)-N(4)

82.0(8)

Er(3)-O(15)

2.252(13)

N(3)-Zn(2)-Cl(1)

108.8(6)

N(3)-Zn(2)-O(6)

88.6(7)

N(3)-Zn(2)-O(7)

135.5(7)

O(2)-Er(2)-O(3)

67.5(5)

O(6)-Er(3)-O(7)

68.1(6)

O(10)-Er(1)-O(11)

139.7(5)

O(13)-Er(1)-O(14)

61.5(5)

O(1)-Er(2)-O(4)

141.3(5)

O(14)-Er(2)-O(15)

77.1(5)

O(13)-Er(3)-O(15)

67.1(5) Zn(1)··· Er(2)

3.433(3)

Zn(2) · ··Er(3)

3.472(3)

Er(1) ··· Er(2)

3.5653(14)

Er(2) ··· Er(3)

3.4631(14)

Er(1) ··· Er(3)

3.5395(14)

30

Table 3 The photophysical properties of ligand H2L, precursor [Zn(L)(MeCN)] and complexes 2-5 and 7-10 at 1×10-5 M in absolute MeCN solution at room temperature or 77 K

Compound

Absorption

Excitation

Emission

λab/nm [log(ε/dm3 mol-1cm-1)]

λex/nm

λem/nm (τ, Φ ×103 )

H 2L

220(1.14), 258(0.54), 327(0.11)

300, 365

480(s, 1.16 ns, 11.0)

[Zn(L)(MeCN)]

236(0.76), 276(0.32), 362(0.17)

328, 400

494(s, 1,56 ns, 15.6)

2

229(1.71), 258(0.95), 344(0.25)

296(sh), 350

462(w,

Temperature-dependent self-assembly of near-infrared (NIR) luminescent Zn2Ln and Zn2Ln3 (Ln=Nd, Yb or Er) complexes from the flexible Salen-type Schiff-base ligand.

Through the self-assembly of the precursor [Zn(L)(MeCN)] (H2L=N,N'-bis(3-methoxy-salicylidene)cyclohexane-1,2-diamine) with LnCl3·6H2O (Ln=La, Nd, Yb,...
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