Synthesis, Crystal Structure, and Photoluminescence of Coordination

Synthesis, Crystal Structure, and Photoluminescence of Coordination Polymers with Mixed Ligands and Diverse Topologies Zhi Su, Jing Xu, Jian Fan, De-Jun Liu, Qian Chu, Man-Sheng Chen, Shui-Sheng Chen, Guang-Xiang Liu, Xiao-Feng Wang, and Wei-Yin Sun*

CRYSTAL GROWTH & DESIGN 2009 VOL. 9, NO. 6 2801–2811

Coordination Chemistry Institute, State Key Laboratory of Coordination Chemistry, School of Chemistry and Chemical Engineering, Nanjing National Laboratory of Microstructures, Nanjing UniVersity, Nanjing 210093, China ReceiVed January 18, 2009; ReVised Manuscript ReceiVed March 26, 2009

ABSTRACT: This work presents systematic investigation on reactions of zinc(II) salts with a rigid tripodal ligand in the presence of different benzenedicarboxylic acids. Seven new coordination polymers [Zn(tib)(1,3-BDC)] · H2O (1), [Zn2(tib)(1,3-BDC)2(H2O)] · 2H2O (2), [Zn2(tib)(1,2-BDC)Cl2] (3), [Zn4(tib)2(1,2-BDC)4] · 2H2O (4), [Zn2(tib)2(1,2-BDC)](NO3)2 (5), [Zn2(tib)2(1,2-BDC)]I2 (6), and [Zn3(tib)2(4-BPA)Cl4] · 2H2O (7) [tib ) 1,3,5-tris(1-imidazolyl)benzene, 1,3-BDC2- ) 1,3-benzenedicarboxylate, 1,2-BDC2) 1,2-benzenedicarboxylate, 4-BPA2- ) 4-bromo-1,2-benzenedicarboxylate] were obtained, and they were characterized by single crystal X-ray diffraction, IR, thermogravimetric and elemental analyses. Complexes 1, 4, and 7 are two-dimensional (2D) networks containing infinite one-dimensional (1D) Zn(II)-tib chains linked together by auxiliary dicarboxylate ligands. Complexes 2 with 2-fold interpenetration and 3 are three-dimensional (3D) frameworks containing infinite 2D networks pillared by 1,2-BDC2- ligands, while 5 and 6 feature unusual 3D supramolecular architectures with 4.82 networks linked by 1,2-BDC2- ligands. The results showed that the dicarboxylate auxiliary ligands and the counteranions have a great influence on the structure of the complexes. The luminescence properties of 1-7 in the solid state were studied. Introduction Recently, remarkable progress has been achieved in the study of metal-organic frameworks (MOFs), not only due to their diverse topology and intriguing structures1 but also owing to their interesting physical and chemical properties, such as photoluminescence, magnetism, ferroelectricity, gas storage, ion exchange, catalysis, etc.2-7 It is known that the construction of MOFs mainly depends on the nature of organic bridging unit and metal ion as well as the counteranions. There are reported studies using flexible bis(imidazole) and rigid multicarboxylate as mixed ligands to build multidimensional frameworks with varied structures and topologies since both flexible bis(imidazole) ligand and multicarboxylate can adopt a variety of coordination modes to satisfy the coordination geometric requirements of the metal ions.8 However, MOFs with rigid imidazole-containing ligand and carboxylate as auxiliary ligand are less documented so far.9 As reported previously, the rigid tripodal ligand 1,3,5-tris(1-imidazolyl)benzene) (tib) is an efficient and versatile organic building unit for construction of coordination architectures, and a variety of MOFs with interesting structures, topologies and properties have been obtained.10 In this study, we focus our attention on reactions of tib, varied Zn(II) salts together with different benzenedicarboxylic acid as auxiliary ligand and performed systematic investigation on the impact of dicarboxylate auxiliary ligands and the counteranions on the structure of the complexes. Herein, we report the syntheses, crystal structures, and photoluminescence properties of seven new tib-Zn(II) coordination polymers with three different benzenedicarboxylate auxiliary ligands, namely, [Zn(tib)(1,3-BDC)] · H2O (1), [Zn2(tib)(1,3-BDC)2(H2O)] · 2H2O (2), [Zn2(tib)(1,2-BDC)Cl2] (3), [Zn4(tib)2(1,2-BDC)4] · 2H2O (4), [Zn2(tib)2(1,2-BDC)](NO3)2 (5), [Zn2(tib)2(1,2-BDC)]I2 (6), and [Zn3(tib)2(4-BPA)Cl4] · 2H2O (7) (1,3-BDC2- ) 1,3-benzenedicarboxylate, 1,2-BDC2- ) 1,2-benzenedicarboxylate, 4-BPA2* Corresponding author. Telephone: +86-25-83593485; fax: +86-2583314502; e-mail: [email protected].

) 4-bromo-1,2-benzenedicarboxylate). All the compounds are characterized by elemental analysis, X-ray crystallography, and thermal stability analysis. The topological analysis and photoluminescence in the solid state were investigated for 1-7. Experimental Section All the commercial available chemicals and solvents are of reagent grade and used as received without further purification. The tib ligand was synthesized according to the method reported previously.10b Elemental analyses for C, H, and N were performed on a Perkin-Elmer 240C Elemental analyzer at the analysis center of Nanjing University. Thermogravimetric analyses (TGA) were performed on a simultaneous SDT 2960 thermal analyzer under nitrogen with a heating rate of 10 °C min-1. FT-IR spectra were recorded in the range of 400-4000 cm-1 on a Bruker Vector22 FT-IR spectrophotometer using KBr pellets. The luminescence spectra for the powdered solid samples were measured on an Aminco Bowman Series 2 spectrofluorometer with a xenon arc lamp as the light source. In the measurement of emission and excitation spectra the pass width is 5 nm, and all the measurements were carried out under the same experimental conditions. Preparation of [Zn(tib)(1,3-BDC)] · H2O (1). A mixture containing ZnCl2 (13.6 mg, 0.1 mmol), tib (27.6 mg, 0.1 mmol), 1,3-H2BDC (16.6 mg, 0.1 mmol), and NaOH (8 mg, 0.2 mmol) in 10 mL of H2O was sealed in a 16 mL Teflon lined stainless steel container and heated at 180 °C for 3 days. Colorless platelet crystals of 1 were collected by filtration and washed with water and ethanol several times with a yield of 57%. Anal. Calcd for C23H18N6O5Zn (%): C, 52.74; H, 3.46; N, 16.04; Found: C, 52.78; H, 3.39; N, 15.97. IR (KBr pellet, cm-1): 3418 (m, br), 1617 (s), 1564 (m), 1509 (m), 1496 (m), 1387 (w), 1352 (m), 1244 (m), 1100 (m), 1074 (m), 1012 (m), 847 (m), 758(w), 721 (w), 650 (m). Preparation of [Zn2(tib)(1,3-BDC)2(H2O)] · 2H2O (2). The title complex was obtained by a procedure similar to that used for 1 except for using Zn(NO3)2 · 6H2O (29.7 mg, 0.1mmol) instead of ZnCl2 as the starting material. Colorless block crystals of 2 were isolated and washed with water and ethanol several times in 61% yield. Anal. Calcd for C31H26N6O11Zn2 (%): C, 47.17; H, 3.32; N, 10.65; found: C, 47.07; H, 3.29; N, 10.72. IR (KBr pellet, cm-1): 3424 (m, br), 1620 (s), 1552 (s), 1515 (m), 1436 (m), 1390 (s), 1354 (s), 1264 (m), 1138(m), 1070 (m), 1015 (m), 950 (m), 850 (m), 734 (s), 672 (w), 648 (w), 556 (w). Preparation of [Zn2(tib)(1,2-BDC)Cl2] (3). Complex 3 was also obtained by hydrothermal procedure as that for 1 just using 1,2-H2BDC

10.1021/cg900059m CCC: $40.75  2009 American Chemical Society Published on Web 04/22/2009

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Su et al.

Table 1. Crystal Data and Structure Refinements for Complexes 1-7

empirical formula formula weight temperature/K crystal system space group a /Å b /Å c /Å R /° β /° γ /° V (Å3) Z Dc (g cm-3) F(000) θ range /° reflns collected independent reflns goodness-of-fit R1a (I > 2σ (I)) wR2b (I > 2σ (I)) a

1

2

3

4

5

6

7

C23H18N6O5Zn 523.79 293(2) monoclinic P21/c 9.6268(15) 12.892(2) 17.778(3) 90 90.000(2) 90 2206.4(6) 4 1.571 1064 1.95-25.99 11632 4324 1.018 0.0411 0.0938

C31H26N6O11Zn2 789.32 293(2) monoclinic P21/n 13.8446(12) 15.6176(14) 15.4016(14) 90 105.371(2) 90 3211.0(5) 4 1.633 1608 1.89-25.00 15740 5636 1.024 0.0545 0.1191

C23H16Cl2N6O4Zn2 642.06 293(2) monoclinic P21/n 11.1930(17) 17.775(3) 12.4971(18) 90 110.768(3) 90 2324.8(6) 4 1.834 1288 2.09-25.24 11688 4205 0.987 0.0412 0.0840

C62H44N12O18Zn4 1506.57 293(2) orthorhombic Pca21 25.7057(17) 11.8041(8) 20.9672(13) 90 90 90 6362.1(7) 4 1.573 3056 1.86-25.25 31113 10538 0.979 0.0523 0.1096

C19H14N7O5Zn 485.74 293(2) monoclinic C2/c 29.470(5) 9.7036(15) 14.674(2) 90 114.343(5) 90 3823.2(11) 8 1.688 1976 2.23-25.24 9463 3458 0.955 0.0438 0.0745

C19H14IN6O2Zn 550.63 293(2) monoclinic C2/c 30.386(4) 9.6758(10) 15.0141(16) 90 116.780(3) 90 3940.8(8) 8 1.856 2152 2.23-25.25 9661 3547 1.068 0.0583 0.1505

C38H31BrCl4N12O6Zn3 1169.54 293(2) triclinic P1j 12.2042(13) 13.5443(15) 13.9699(14) 89.426(2) 73.780(3) 82.520(2) 2197.6(4) 2 1.761 1160 1.75-25.05 11043 7634 0.886 0.0516 0.1139

R1 ) Σ|Fo - Fc|/Σ Fo. b wR2 ) Σw(Fo2 - Fc2) /Σ w(Fo)2

, where w ) 1/[σ2(Fo2) + (aP)2 + bP]. P ) (Fo2 + 2Fc2)/3.

1/2

(16.6 mg, 0.1 mmol) rather than 1,3-H2BDC as the starting reactant. Colorless block crystals of 3 were collected in 49% yield after washing with water and ethanol several times. Anal. Calcd for C23H16Cl2N6O4Zn2 (%): C, 43.02; H, 2.51; N, 13.09; found: C, 42.92; H, 2.49; N, 13.17. IR (KBr pellet, cm-1): 3448 (m, br), 1621 (w), 1608 (s), 1587 (m), 1560 (m), 1521 (m), 1408 (s), 1346 (m), 1274 (w), 1252 (m), 1106 (w), 1077 (s), 1015 (m), 952 (m), 859 (w), 838 (w), 752 (m), 723 (m), 650 (m), 578 (w). Preparation of [Zn4(tib)2(1,2-BDC)4] · 2H2O (4). Similar procedures were performed to obtain the colorless block crystals of 4, except that Zn(OAc)2 · 2H2O (21.9 mg, 0.1 mmol) was used instead of ZnCl2 used for preparation of 3. The yield is 68% based on the Zn(OAc)2 · 2H2O. Anal. Calcd for C62H44N12O18Zn4 (%): C, 49.43; H, 2.94; N, 11.16; found: C, 49.48; H, 2.87; N, 11.19. IR (KBr pellet, cm-1): 3441(m, br), 1616 (s), 1565 (s), 1515 (s), 1389 (s), 1320 (m), 1265 (m), 1119 (w), 1081 (m), 1014 (m), 947 (m), 833 (w), 760 (m), 700 (w), 651 (m), 576 (w). Preparation of [Zn2(tib)2(1,2-BDC)](NO3)2 (5). Similar procedures were used to synthesize the colorless block crystals of complex 5, except that Zn(NO3)2 · 6H2O (29.7 mg, 0.1 mmol) was used instead of ZnCl2 used for preparation of 3. The yield is 63% based on the Zn(NO3)2 · 6H2O. Anal. Calcd for C19H14N7O5Zn (%): C, 46.98; H, 2.91; N, 20.18; found: C, 46.95; H, 3.04; N, 20.10. IR (KBr pellet, cm-1): 3448 (m,br), 1619 (s), 1578 (s), 1534(m), 1518 (m), 1383 (s), 1332 (m) 1270 (m), 1110 (w), 1090 (w), 1074 (w), 948 (w), 867 (w), 760 (m), 675 (w), 652 (w). Preparation of [Zn2(tib)2(1,2-BDC)]I2 (6). Complex 6 was synthesized by the same procedures used for 3, except that ZnI2 (31.9 mg, 0.1 mmol) was used instead of ZnCl2 as the starting material. Colorless block crystals of 6 were obtained in 63% yield. Anal. Calcd for C19H14IN6O2Zn (%): C, 41.44; H, 2.56; N, 15.26; found: C, 41.37; H, 2.61; N, 15.29. IR (KBr pellet, cm-1): 3385 (m, br), 1617 (m), 1578 (m), 1530 (s), 1404 (s), 1320 (w), 1266 (m), 1111 (m), 1076 (m), 1016 (m), 948 (m), 853 (w), 752 (m), 712 (w), 672 (w), 648 (m). Preparation of [Zn3(tib)2(4-BPA)Cl4] · 2H2O (7). A mixture of ZnCl2 (13.6 mg, 0.1 mmol), tib (27.6 mg, 0.1 mmol), 4-H2BPA (24.6 mg, 0.1mmol), and tetrabutylammonium hydroxide solution (10%) (0.5 mL) in 10 mL of H2O were sealed in a 16 mL Teflon lined stainless steel container and heated at 180 °C for 3 days. Colorless block crystals were collected in 46% yield. Anal. Calcd for C38H31BrCl4N12O6Zn3 (%): C, 39.00; H, 2.67; N, 14.37; found: C, 38.89; H, 2.76; N, 14.45. IR (KBr pellet, cm-1): 3421 (m, br), 3129 (m), 1619 (s), 1514 (s), 1375 (m), 1316 (w), 1267 (m), 1253 (m), 1073 (s), 1015 (m), 947 (m), 874 (w), 841 (w), 759 (w), 648 (w). Crystallography. The crystallographic data collections for 1-7 were carried out on a Bruker Smart Apex CCD area-detector diffractometer with graphite-monochromated Mo KR radiation (λ ) 0.71073 Å) at 20(2) °C using ω-scan technique. The diffraction data was integrated by using the SAINT program,11 which was also used for the intensity corrections for the Lorentz and polarization effects. Semiempirical absorption correction was applied using the SADABS program.12 The

structures were solved by direct methods and all the non-hydrogen atoms were refined anisotropically on F2 by the full-matrix least-squares technique using the SHELXL-97 crystallographic software package.13 The nitrate anion in 5 disordered into two positions with site occupancy factors of 0.49(2) and 0.51(2), respectively. Details of the crystal parameters, data collection, and refinements for 1-7 are summarized in Table 1. Selected bond lengths and angles for 1-7 are listed in Table 2. Further details are provided in the Supporting Information.

Results and Discussion Crystal Structure of [Zn(tib)(1,3-BDC)] · H2O (1). The polymeric structure of 1 was confirmed by X-ray single crystal structure determination. The coordination environment around the Zn(II) atom is exhibited in Figure 1a along with the atom numbering scheme. Each Zn(II) with distorted tetrahedral coordination geometry is four-coordinated by two N atoms (N1A, N3) from two different tib ligands with Zn1-N distances of 2.010(2) and 2.027(2) Å and two O atoms (O1, O3A) from two distinct 1,2-BDC2- with Zn1-O bond lengths of 1.9355(18) and 1.9565(18) Å, respectively (Table 2). It is noteworthy that each tib ligand coordinates with two, rather than three, zinc(II) atoms using two of its three imidazole groups, and the third one with N5 does not participate in the coordination, probably due to the rigidity of the tib ligand; namely, the tib in 1 acts as a two-connecting (bridging) ligand which has been observed previously.6b,10a,b On the other hand, the 1,2-BDC2- is also a bridging ligand since each carboxylate group adopts a µ1-η1:η0 monodentate coordination mode to connect one Zn(II) atom (Type I, Scheme 1). Such coordination modes make complex 1 a neutral 2D rectangular grid network with (4, 4) topology since the angles formed between the Zn(II) nodes (e.g., Zn1D-Zn1EZn1F, Zn1E-Zn1F-Zn1G) are 90° (Figure 1b), which can be seen clearly from a simplified 2D network where only the Zn(II) atoms are presented (Figure 1c). In each Zn4 grid, the Zn · · · Zn edge distances are 9.63 Å for Zn1D · · · Zn1G and Zn1E · · · Zn1F, 12.92 Å for Zn1D · · · Zn1E and Zn1F · · · Zn1G (Figure 1b), respectively. Furthermore, the 2D layers are further linked together by C-H · · · O and C-H · · · N hydrogen bonds to generate a three-dimensional (3D) structure (Figure S1, Supporting Information). The hydrogen bonding data are summarized in Table S1, Supporting Information. Crystal Structure of [Zn2(tib)(1,3-BDC)2(H2O)] · 2H2O (2). The reaction of tib and 1,3-BDC2- with Zn(NO3)2 · 6H2O, instead of ZnCl2, under the same reaction conditions was carried

Synthesis of Coordination Polymers

Crystal Growth & Design, Vol. 9, No. 6, 2009 2803

Table 2. Selected Bond Lengths [Å] and Bond Angles [deg] for Complexes 1-7a 1 Zn(1)-O(1) Zn(1)-N(1) O(1)-Zn(1)-O(3)#1 O(3)#1-Zn(1)-N(1) O(3)#1-Zn(1)-N(3)#2

1.9355(18) 2.010(2) 119.31(8) 107.43(9) 97.56(8)

Zn(1)-O(4)#3 Zn(1)-N(3) Zn(2)-O(1) Zn(2)-N(1) Zn(2)-O(8)#5 O(4)#3-Zn(1)-O(5) O(4)#3-Zn(1)-N(3) O(5)-Zn(1)-N(3) O(1)-Zn(2)-N(1) O(1)-Zn(2)-O(9) N(1)-Zn(2)-O(9) O(1)-Zn(2)-O(7)#5 N(1)-Zn(2)-O(7)#5

1.945(4) 2.009(3) 1.934(3) 1.997(4) 2.280(4) 116.99(16) 99.72(15) 116.81(17) 132.03(16) 97.45(19) 101.3(2) 120.47(15) 103.64(17)

Zn(1)-O(2) Zn(1)-O(4)#6 Zn(2)-O(3) Zn(2)-N(5)#8 O(2)-Zn(1)-O(4)#6 O(2)-Zn(1)-N(3)#7 O(4)#6-Zn(1)-N(3)#7 O(3)-Zn(2)-N(5)#8 O(3)-Zn(2)-Cl(2) N(5)#8-Zn(2)-Cl(2)

1.945(3) 1.955(2) 1.957(3) 2.016(3) 119.32(12) 124.25(12) 104.87(12) 92.08(11) 115.35(9) 110.86(10)

Zn(1)-O(2) Zn(1)-N(7) Zn(1)-O(10) Zn(2)-O(16) Zn(2)-N(1) Zn(3)-O(4) Zn(3)-N(9)#9 Zn(3)-O(5) Zn(4)-O(13) Zn(4)-N(5)#11 O(2)-Zn(1)-N(7) O(2)-Zn(1)-O(8) N(7)-Zn(1)-O(8) O(2)-Zn(1)-O(6) N(7)-Zn(1)-O(6) O(16)-Zn(2)-N(1) O(16)-Zn(2)-O(10) N(1)-Zn(2)-O(10) O(16)-Zn(2)-O(8) N(1)-Zn(2)-O(8) O(4)-Zn(3)-N(9)#9 O(4)-Zn(3)-O(5) N(9)#9-Zn(3)-O(5) O(4)-Zn(3)-N(11)#10 N(9)#9-Zn(3)-N(11)#10 O(13)-Zn(4)-N(5)#11 O(13)-Zn(4)-O(11) N(5)#11-Zn(4)-O(11)

1.971(5) 2.016(6) 2.117(5) 1.986(5) 2.026(5) 1.934(5) 2.018(5) 2.018(5) 1.907(5) 2.021(6) 112.3(2) 144.4(2) 102.7(2) 95.42(19) 99.6(2) 115.3(2) 142.6(2) 101.8(2) 96.9(2) 93.7(2) 107.7(2) 128.4(2) 106.9(2) 106.5(2) 114.0(2) 109.4(2) 125.0(2) 93.4(2)

Zn(1)-O(1) Zn(1)-N(1) O(1)-Zn(1)-N(1) O(1)-Zn(1)-N(3)#13 N(1)-Zn(1)-N(3)#13

1.993(2) 1.998(3) 114.19(11) 98.63(10) 111.17(11)

Zn(1)-O(1) Zn(1)-N(3)#15 O(1)-Zn(1)-N(3)#15 O(1)-Zn(1)-N(5)#16 N(3)#15-Zn(1)-N(5)#16

1.986(4) 1.993(4) 113.60(17) 99.31(17) 109.69(18)

Zn(1)-N(7) Zn(1)-N(5) Zn(2)-O(3)#17 Zn(2)-N(1) Zn(3)-O(2) Zn(3)-N(3)#19 N(7)-Zn(1)-N(5) N(7)-Zn(1)-Cl(2) N(5)-Zn(1)-Cl(2) O(3)#17-Zn(2)-N(1) O(3)#17-Zn(2)-N(9)#18 N(1)-Zn(2)-N(9)#18 O(2)-Zn(3)-N(3)#19 O(2)-Zn(3)-N(11) N(3)#19-Zn(3)-N(11)

2.015(4) 2.026(4) 1.938(4) 2.008(4) 1.957(3) 2.008(4) 116.40(18) 108.09(13) 105.34(13) 116.47(17) 104.91(17) 108.92(18) 123.10(16) 96.81(17) 109.07(17)

Zn(1)-O(3)#1 Zn(1)-N(3)#2 O(1)-Zn(1)-N(1) O(1)-Zn(1)-N(3)#2 N(1)-Zn(1)-N(3)#2

1.9565(18) 2.027(2) 108.62(8) 116.30(9) 106.49(9)

2 Zn(1)-O(5) Zn(1)-N(5)#4 Zn(2)-O(9) Zn(2)-O(7)#5

1.952(4) 2.020(4) 2.042(4) 2.091(4)

O(4)#3-Zn(1)-N(5)#4 O(5)-Zn(1)-N(5)#4 N(3)-Zn(1)-N(5)#4 O(9)-Zn(2)-O(7)#5 O(1)-Zn(2)-O(8)#5 N(1)-Zn(2)-O(8)#5 O(9)-Zn(2)-O(8)#5 O(7)#5-Zn(2)-O(8)#5

114.00(17) 101.85(16) 107.70(15) 89.14(17) 94.29(15) 92.63(19) 147.83(17) 59.24(14)

Zn(1)-N(3)#7 Zn(1)-N(1) Zn(2)-Cl(2) Zn(2)-Cl(1) O(2)-Zn(1)-N(1) O(4)#6-Zn(1)-N(1) N(3)#7-Zn(1)-N(1) O(3)-Zn(2)-Cl(1) N(5)#8-Zn(2)-Cl(1) Cl(2)-Zn(2)-Cl(1)

1.998(3) 2.033(3) 2.2170(11) 2.2331(11) 101.55(12) 100.31(11) 102.12(12) 109.77(9) 117.04(10) 110.74(4)

3

4 Zn(1)-O(8) Zn(1)-O(6) Zn(2)-O(12) Zn(2)-O(10) Zn(2)-O(8) Zn(3)-N(11)#10 Zn(3)-O(6) Zn(4)-O(11) Zn(4)-N(3)#12

2.064(5) 2.094(5) 2.113(5) 2.060(5) 2.108(5) 2.025(5) 2.441(5) 2.023(5) 2.028(5)

O(8)-Zn(1)-O(6) O(2)-Zn(1)-O(10) N(7)-Zn(1)-O(10) O(8)-Zn(1)-O(10) O(6)-Zn(1)-O(10) O(10)-Zn(2)-O(8) O(16)-Zn(2)-O(12) N(1)-Zn(2)-O(12) O(10)-Zn(2)-O(12) O(8)-Zn(2)-O(12) O(5)-Zn(3)-N(11)#10 O(4)-Zn(3)-O(6) N(9)#9-Zn(3)-O(6) O(5)-Zn(3)-O(6) N(11)#10-Zn(3)-O(6) O(13)-Zn(4)-N(3)#12 N(5)#11-Zn(4)-N(3)#12 O(11)-Zn(4)-N(3)#12

84.16(19) 95.6(2) 94.8(2) 75.10(17) 156.9(2) 75.39(17) 93.7(2) 99.9(2) 83.9(2) 157.2(2) 92.7(2) 85.32(19) 90.15(19) 57.59(18) 147.1(2) 110.0(2) 112.8(3) 105.3(2)

Zn(1)-N(3)#13 Zn(1)-N(5)#14 O(1)-Zn(1)-N(5)#14 N(1)-Zn(1)-N(5)#14 N(3)#13-Zn(1)-N(5)#14

2.009(3) 2.021(3) 126.60(10) 105.45(11) 98.85(11)

Zn(1)-N(5)#16 Zn(1)-N(1) O(1)-Zn(1)-N(1) N(3)#15-Zn(1)-N(1) N(5)#16-Zn(1)-N(1)

2.021(4) 2.027(4) 125.67(18) 106.13(18) 100.54(19)

Zn(1)-Cl(2) Zn(1)-Cl(1) Zn(2)-N(9)#18 Zn(2)-Cl(4) Zn(3)-N(11) Zn(3)-Cl(3) N(7)-Zn(1)-Cl(1) N(5)-Zn(1)-Cl(1) Cl(2)-Zn(1)-Cl(1) O(3)#17-Zn(2)-Cl(4) N(1)-Zn(2)-Cl(4) N(9)#18-Zn(2)-Cl(4) O(2)-Zn(3)-Cl(3) N(3)#19-Zn(3)-Cl(3) N(11)-Zn(3)-Cl(3)

2.2169(16) 2.2778(17) 2.034(4) 2.2376(16) 2.019(4) 2.2508(17) 99.26(14) 100.90(13) 127.53(7) 113.34(12) 107.65(13) 104.83(14) 110.22(12) 106.16(14) 111.09(14)

5

6

7

a Symmetry transformations used to generate equivalent atoms: #1 x - 1, y, z; #2 x, -y + 3/2, z - 1/2; #3 x - 1, y - 1, z; #4 x - 1/2, -y + 1/2, z + 1/2; #5 x, y + 1, z; #6 x + 1/2, -y + 1/2, z + 1/2; #7 -x + 3/2, y + 1/2, -z + 1/2; #8 x - 1/2, -y + 1/2, z + 1/2; #9 x + 1/2, -y, z; #10 x + 1/ 2, -y + 1, z; #11 x - 1/2, -y - 1, z; #12 x - 1/2, -y, z; #13 -x + 1/2, -y + 5/2, -z; #14 -x + 1/2, y + 1/2, -z + 1/2; #15 -x + 1/2, y + 1/2, -z + 3/2; #16 x, -y, z - 1/2; #17 -x + 2, -y + 1, -z; #18 -x + 2, -y + 1, -z - 1; #19 -x + 2, -y + 2, -z.

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Figure 1. (a) Coordination environment of zinc(II) in complex 1 with ellipsoids drawn at the 30% probability level; hydrogen atoms and free water molecules were omitted for clarity. (b) The 2D grid network of 1. (c) The 2D sheet consists of rectangular grids with (4, 4) topology, and only the zinc(II) atoms are presented.

out to investigate the influence of counteranion on the reaction, and a new complex 2 with 3D structure was obtained. X-ray crystallographic analysis revealed that 2 crystallizes in monoclinic form with space group P21/n. There are two Zn(II) atoms with different coordination environments, two 1,3-BDC2- with different coordination modes, one tib and one coordinated and two uncoordinated water molecules in the asymmetric unit of 2. As illustrated in Figure 2a, each Zn1 is coordinated by two N atoms (N3A, N5) from two different tib ligands with Zn1-N bond lengths of 2.009(3) and 2.020(4) Å, and two O atoms (O4A, O5) from two distinct 1,3-BDC2- with Zn1-O bond lengths of 1.945(4) and 1.952(4) Å, respectively. The bond angles around Zn1 are in the range of 99.72(15)-116.99(16)° (Table 2). Thus, the local coordination geometry of Zn1 is

slightly distorted tetrahedral with a N2O2 donor set. While in the case of Zn2, each Zn2 is five-coordinated by three O atoms (O2, O7A, O8A) from two separated 1,3-BDC2- and the additional two positions are occupied by a terminal water molecule (O9) and a N atom (N1) from tib ligand with an average Zn2-O bond length of 2.087 Å and Zn2-N bond length of 1.997(4) Å (Table 2). On the other hand, each tib ligand links three Zn(II) atoms in 2 to form an infinite 1D chain, which is different from the coordination mode of tib in 1 as a 2-connected (bridging) node. The adjacent Zn-tib chains are further linked by 1,3-BDC2ligands to give a 2D honeycomb network through the Zn-O coordination interactions using two carboxylate groups adopting µ1-η1:η0-monodentate and µ1-η1:η1-chelating modes, respectively (Type II, Scheme 1), and a 46-membered macrocyclic ring with five Zn(II), two 1,3-BDC2-, and three tib was formed as depicted in Figure 2b. Furthermore, the 2D sheets are further connected together via Zn-O bonds by the other 1,3-BDC2- ligands, both the carboxylate groups adopting a µ1-η1:η0-monodentate coordination mode (Type I, Scheme 1), to give a 3D framework in which there are open channels with dimensions of 13.99 × 13.85 Å, to allow one net to be penetrated by another independent net (Figure 2c,d). In other words, the entire structure of 2 is a 3D framework with 2-fold interpenetration. A better insight into the nature of this intricate architecture can be achieved by the application of a topological approach, reducing multidimensional structures to simple node-and-linker net, and topological analysis was carried out for 2. Each Zn1 connects two tib ligands (vide supra) and two 1,3-BDC2ligands; hence, each Zn1 can be regarded as a 4-connected node. Each Zn2 atom in turn connects one tib ligand and two 1,3BDC2- ligands; thus, each Zn2 can be regarded as a 3-connected node. Meanwhile, each tib ligand connects three Zn(II) atoms using its three arms, and thus each tib can be treated as



Figure 2. (a) The coordination environment around the zinc(II) atoms in complex 2 with ellipsoids drawn at the 30% probability level; hydrogen atoms and free water molecules were omitted for clarity. (b) Side (left) and top (right) views of the 2D structure with 46-membered rings. (c) The 3D structure of 2. (d) 2-fold interpenetrated 3D structure of 2. (e) Schematic drawing of the 3D (3,4)-connected network in which tib ligand is represented by three spokes radiating from the centroid of the benzene ring to Zn(II) centers directly.

3-connected node. Both the 1,3-BDC2- ligands connect two Zn(II) atoms, and thus they can be treated as 2-connected nodes. Such connectivity repeats infinitely to give the 3D framework as schematically shown in Figure 2e. According to the simplification principle,14 the resulting structure of 2 is a trinodal (3,4)connected net, and its Schla¨fli symbol is (83)2(86) (the first symbol is for the tib ligands and Zn2 atoms, and the second is for the Zn1 atoms). Crystal Structure of [Zn2(tib)(1,2-BDC)Cl2] (3). In addition to the 1,3-BDC2- bridging auxiliary ligand used in construction of 1, 2 as described above, 1,2-H2BDC was also employed in the reactions of tib with Zn(II) salts and complexes 3-6 were isolated. The polymeric structure of 3 was evidenced by X-ray single crystal structure determination. The asymmetric unit of 3, as illustrated in Figure 3a, consists of a binuclear unit with two nonequivalent Zn(II) atoms (Zn1 and Zn2). The Zn1 with distorted tetrahedral coordination geometry is four-coordinated by two N atoms (N1 and N3A) from two different tib ligands and two O atoms (O2 and O4A) from two distinct 1,2-BDC2-. The Zn1-O distances are 1.945(3) and 1.955(2) Å, and the Zn1-N ones are 1.998(3) and 2.033(3) Å, respectively (Table 2). The Zn2 has the same tetrahedral coordination geometry with that of Zn1 but a different coordination environment; two Cl- (Cl1 and Cl2) as the terminal ligands coordinate to Zn2 instead of one N and one O atom, with Zn2-Cl bond lengths

of 2.2331(11) and 2.2170(11) Å, respectively (Table 2). Thus, the coordination geometry of Zn(II) atoms in 3 is same as that in 1; however, it is clear that there are differences between 1 and 3. The first difference is that there are two crystallographic different Zn(II) atoms in 3, while only one in 1. The second one is that the chlorides joined into the structure as terminal ligands and counteranions in 3, while no chlorides were found in 1. The third difference is that three arms of tib ligand connect to three Zn(II) atoms in 3, while only two of three arms take part in the coordination with Zn(II) in 1. Each tib ligand in 3 links three Zn(II) atoms to form an infinite 1D chain using its three imidazole arms. If the coordination linkage between the carboxylate group adopting a µ1-η1:η0monodentate mode and Zn(II) is neglected, a 2D honeycomb network was obtained via the Zn-O coordination bonds of the carboxylate adopting a µ2-η1:η1-bridging mode of 1,2-BDC2(Type V, Scheme 1) and the Zn-N coordination of imidazole groups of tib ligands as illustrated in Figure 3b. There are 38membered macrocycles in the 2D sheet, formed by six imidazole arms from three tib ligands and two bridging carboxylate units from two 1,2-BDC2- ligands together with five Zn(II) atoms. The intermetallic separation of Zn1A · · · Zn2A, Zn1B · · · Zn2B, Zn1A · · · Zn1C are 11.53, 11.69, 11.81 Å, respectively, and Zn1B · · · Zn2A ) Zn1C · · · Zn2B is 4.84 Å. Such 2D layers are further connected by the µ1-η1:η0-monodentate carboxylate units

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Figure 3. (a) Coordination environment of zinc(II) atoms in 3 with ellipsoids drawn at the 30% probability level; hydrogen atoms are omitted for clarity. (b) Side (left) and top (right) views of the 2D structure with a 38-membered rings. (c) The 3D structure of complex 3. (d) Schematic drawing of 3D (3,4)-connected framework in which the tib ligand is represented by three green spokes radiating from the centroid of the benzene ring to Zn(II) centers and 1,2-BDC2- is shown by a red one.

of the 1,2-BDC2- ligands (Type V, Scheme 1) to give a 3D architecture (Figure 3c). Similar topological analysis was carried out to get insight of the structure of 3; each tib ligand and 1,2-BDC2- are neighbored by three Zn(II) atoms, and thus each tib and 1,2-BDC2- can be regarded as 3-connector, respectively. Meanwhile, each Zn1 atom links two tib ligands and two 1,2-BDC2- ligands; hence, Zn1 atom can be regarded as 4-connector, and each Zn2 atom can be viewed as 2-connector through omitting the coordination of two chloride anions. Such connectivity repeats infinitely to give the 3D framework as depicted in Figure 3d. According to the simplification principle, the resulting structure of complex 3 is a trinodal (3,4)-connected net, with its Schla¨fli symbol (6, 82)2(6, 85). Crystal Structure of [Zn4(tib)2(1,2-BDC)4] · 2H2O (4). When Zn(OAc)2 · 2H2O, instead of ZnCl2, was taken into the reaction with the tib and 1,2-H2BDC, a new coordination polymer 4 with a different structure was isolated. The result of X-ray crystallographic analysis revealed that 4 crystallized in the orthorhombic with space group Pca21 (Table 1). The asymmetric unit of 4 consists of two tib, four 1,2-BDC2- ligands, four different

Zn(II) atoms, and two uncoordinated water molecules. As displayed in Figure 4a, each Zn1 atom with a distorted squarepyramidal coordination geometry is coordinated by four O atoms (O2, O6, O8, O10) from three 1,2-BDC2- ligands and one N atom (N7A) from a tib ligand. The O2, O6, O8, and O10 comprise the equatorial plane, and the apical position is occupied by N7A. The Zn1-O distances range from 1.971(5) to 2.117(5) Å, and the Zn1-N distance is 2.016(6) Å (Table 2). Zn2 has a similar coordination environment and geometry with that of Zn1. Zn3 with distorted square-pyramidal coordination geometry is coordinated by three O atoms (O4, O5, O6) from two 1,2-BDC2ligands and two N atoms (N9A, N11) from two different tib ligands. The average Zn3-O and Zn3-N bond lengths are 2.131 and 2.011 Å, respectively, and the coordination angles around Zn3 are in the range of 57.59(18)-157.2(2)°. Comparably, Zn4 atom with a distorted tetrahedral environment and geometry is coordinated by two O atoms (O11, O13) from two distinct 1,2BDC2- ligands and two N atoms (N3A, N5) from two different tib ligands. The most striking feature of 4 is that four Zn(II) atoms are linked together by four 1,2-BDC2- ligands to form a Zn4 unit



Figure 4. (a) The coordination environment around the zinc(II) atoms in 4 with ellipsoids drawn at the 30% probability level; hydrogen atoms and free water molecules were omitted for clarity. (b) The 2D structure of 4 with the [Zn4(1,2-BDC)4] core.

with Zn · · · Zn separations of 3.31 (Zn1 · · · Zn2), 4.28 (Zn1 · · · Zn3), 4.37 (Zn2 · · · Zn4), and 11.25 Å (Zn3 · · · Zn4), respectively. Furthermore, four 1,2-BDC2- ligands adopt three coordination modes: first, two µ1-η1:η0-monodentate modes (Type IV, Scheme 1); second, µ2-η2:η0-bridging and µ2-η1:η1-bridging mode (Type VII, Scheme 1); third, µ2-η2:η0-bridging and µ2η2:η1-bridging mode (Type VI, Scheme 1). Further connection of the Zn4 unit via the tib ligands leads to the formation of a 2D framework (Figure 4b). When the Zn4 unit was viewed as a node, it links to six tib ligands, and the tib ligand in turn connects three Zn4 units. So the 2D sheet can be simplified to a trinodal (3, 6)-connected net (Figure S2, Supporting Information), and it can be regarded as a (42, 6)2(44, 69, 82) topology. The layers are stacked in -ABAB- sequence along the c-axis (Figure S3a, Supporting Information) with interlayer hydrogenbonding interactions leading to the formation of a 3D network (Figure S3b, Supporting Information). The related hydrogenbonding data with the symmetry codes are given in Table S1, Supporting Information. Crystal Structures of [Zn2(tib)2(1,2-BDC)](NO3)2 (5) and [Zn2(tib)2(1,2-BDC)]I2 (6). As listed in Table 1, complexes 5 and 6 crystallized in the same monoclinic form with space group C2/c and have similar cell parameters, and the results of crystal structure analysis revealed that they have the same framework structure except for the different counteranions; thus, only the structure of 5 is described here as an example. The asymmetric unit of complex 5 consists of one Zn(II) atom, one tib ligand, half 1,2-BDC2-, and one nitrate anion. As shown in Figure 5a, the central Zn(II) atom is four-coordinated by three N atoms (N1A, N3, and N5A) from three different tib ligands and one O atom (O1) from 1,2-BDC2-, with an average Zn1-N

bond length of 2.010 Å and Zn1-O one of 1.993(2) Å, respectively. Thus, the coordination geometry of the central Zn(II) is distorted tetrahedral with N3O donor set. On the other hand, each tib ligand links three Zn(II) to generate a 2D network with two different metallacycles A and B. In A, four imidazole arms from two tib ligands connect two Zn(II) atoms to form a 20-membered ring with a Zn · · · Zn (e.g., Zn1A · · · Zn1B in Figure 5b) distance of 9.64 Å. In B, four tib ligands, each using two of its three arms, link four Zn(II) atoms to give a 40-membered ring with intermetallic distances of Zn1A · · · Zn1C ) Zn1D · · · Zn1E ) 12.82 Å, and Zn1A · · · Zn1E ) Zn1C · · · Zn1D ) 11.33 Å. Accordingly, each 20-membered ring is surrounded by four 40-membered rings, and each 40membered ring neighbors four 20-membered and four 40membered rings. Thus, the 2D network can be regarded as (4, 82) topology, which has been observed in our previously reported complexes (Figure S4a, Supporting Information).10a Furthermore, such kinds of 2D sheets are joined together by 1,2-BDC2to complete the 3D framework structure in which each carboxylate of 1,2-BDC2- has a µ1-η1:η0-monodentate coordination mode (Type IV, Scheme 1, Figure S4b, Supporting Information). As illustrated above, each tib ligand links three and each 1,2BDC2- connects two Zn(II) atoms; thus, they can be treated as 3- and 2-connector (bridging), respectively. Each Zn(II) atom in turn links three tib ligands and one 1,2-BDC2-; hence, it can be treated as 4-connector. Such connectivity repeats infinitely to give the 3D framework as depicted in Figure 5c. According to the simplification principle, the 3D structure of complex 5 is a binodal (3,4)-connected net, with its Schla¨fli symbol (4, 6, 8)(4, 62, 83). Moreover, there are 1D channels with a size about

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Figure 5. (a) Coordination environment of zinc(II) in 5 with ellipsoids drawn at the 30% probability level; hydrogen atoms were omitted for clarity. (b) The 2D layer formed by tib-Zn with 20- and 40-membered metallacycles (A and B) in 5. (c) Schematic drawing of 3D (3,4)-connected framework of 5. (d) 3D structure of 5 with uncoordinated nitrate anion shown in space filling mode occupying the cavities.

6.7 × 7.1 Å in the 3D structure of 5 occupied by the nitrate anions through the C-H · · · O hydrogen bonding interactions (Figures 5d and Figure S5, Supporting Information), which also further consolidate the structure of the complex. Crystal Structure of [Zn3(tib)2(4-BPA)Cl4] · 2H2O (7). To investigate the effect of halide substituted benzenedicarboxylate on the structure of Zn(II) complex, the reaction of 4-H2BPA with tib and ZnCl2 was carried out, and complex 7 was obtained. The X-ray crystallographic analysis showed that 7 crystallized in the triclinic form with space group P1j, and the structure of 7 is a 2D network. In the asymmetric unit, there are three crystallographic independent four-coordinated Zn(II) atoms, two tib ligands, one 4-BPA2-, four chloride, and two uncoordinated water molecules. As shown in Figure 6a, the Zn1 has distorted tetrahedral geometry with N2Cl2 donor set and is coordinated by two N atoms (N5, N7A) from two separate tib ligands and two Cl atoms (Cl1, Cl2). The Zn1-N bond lengths are 2.015(4) and 2.026(4) Å, and the Zn1-Cl ones are 2.2169(16) and 2.2778(17) Å, respectively. Comparably, the Zn2 also with distorted tetrahedral geometry but N2OCl coordination environment is coordinated by two N atoms (N1A, N9) from two distinct tib ligands, one O atom (O3A) from 4-BPA2-, and one Cl (Cl4). The average Zn2-N bond distance is 2.021 Å, the Zn2-O3A one is 1.938(4) Å, and the Zn2-Cl4 one is 2.2376(16) Å, respectively.15 The Zn3 has the same coordination environment and geometry as that of Zn2. Thus, the coordination

geometry of Zn(II) atoms in 7 is same as that in 3; however, there are difference between 7 and 3. One is that there are three crystallographic independent Zn(II) atoms in 7, while only two in 3. Another one is that the ratio of auxiliary ligand to tib in 7 is 1:2, while that in 3 is 1:1. In 7, each tib acts a µ3-bridge to link three Zn(II) centers to complete an infinite 1D chains, and these chains are connected through Zn-O bonds of two carboxylate groups of the 4-BPA2to generate a 2D layer, in which both the carboxylate groups adopt µ1-η1:η0-monodentate mode (Type III, Scheme 1 and Figure 6b). Zn1 links two tib ligands, and hence, it can be viewed as a 2-connector (bridging) when the two terminal coordinated chloride atoms are ignored. Each of Zn2 and Zn3 in turn connects two tib ligands and one 4-BPA2- ligand; thus, they can be thought as 3-connector omitting the terminal chloride anion. As a result, the topology of the 2D layer of 7 is a tetranodal 3-connected net, with its Schla¨fli symbol of (6, 82)(62, 10) (Figure S6a, Supporting Information). The remarkable feature of complex 7 is that there are Br · · · Br interactions involved in the stabilization of the crystal lattice. The Br-Br distance within the range of 3.3-3.9 Å is considered to have Br · · · Br interactions.16 As shown in Figure S6b, Supporting Information, the distance between two nearest Br atoms from the adjacent 2D layers is 3.88 Å in complex 7, and the 2D layers are joined together by such Br · · · Br interactions leading to the formation of a 3D structure. Furthermore, the



Figure 6. (a) Coordination environment of Zn(II) atoms in 7 with ellipsoids drawn at the 30% probability level; hydrogen atoms and free water molecules were omitted for clarity. (b) Side (left) and top (right) views of the 2D structure in 7.

3D polymeric structure is further consolidated by the C-H · · · O and C-H · · · C hydrogen bonds as listed in Table S1, Supporting Information. Thermal Stabilities of the Complexes. Thermogravimetric analyses (TGA) were carried out for the synthesized complexes, and the results are shown in Figure S7, Supporting Information. Complex 1 shows a weight loss of 3.68% below 200 °C corresponding to the release of free water molecules (calcd 3.45%) and the decomposition of the residue occurred at 430 °C. A total weight loss of 6.83% was observed for 2 in the temperature range of 120-220 °C, which is attributed to the loss of both the coordinated and uncoordinated water molecules (calcd 6.84%), and the residue is stable up to about 340 °C. No obviously weight loss was found for complexes 3, 5, and 6 before the decomposition of the framework occurred at about 370, 360, and 360 °C, respectively, which is in good agreement with the results of the crystal structure. For 4, a weight loss of 2.36% was observed in the temperature range of 60-140 °C, which corresponds to the loss of the free water molecules (calcd 2.40%), and further weight loss was observed at about 350 °C. Complex 7 exhibited weight loss in the temperature range of 70-100 °C, and the total loss is about 3.74%, which is in agreement with the departure of lattice water molecules (calcd 3.08%) and the residue is stable up to 310 °C. The Effect of the Auxiliary Ligands and Counteranions. The complete deprotonation of the carboxylate groups of the auxiliary benzenedicarboxylic acid ligands in 1-7 was

confirmed by IR spectral data, since no IR bands in the range of 1760-1680 cm-1 were observed in the IR spectra of 1-7 (see Experimental Section), as well as by the results of crystallographic analysis (vide infra). Comparing complexes 1, 3, and 7 obtained from the same ZnCl2 under the same conditions, it is clear that the different framework structure is ascribed to the different benzenedicarboxylate auxiliary ligands. In complexes 1 and 7, each auxiliary ligand links two Zn(II) atoms through its two µ1-η1:η0-monodentate carboxylate groups to form 2D networks, while in the case of complex 3, each 1,2BDC2- links three Zn(II) atoms using µ1-η1:η0-monodentate and µ2-η1:η1-bridging carboxylate groups to produce a 3D framework. Furthermore, the sterically hindered 4-BPA2- ligand due to the presence of the bromine atom may also cause the formation of a 2D network for complex 7. In addition, it is worth noting that there are Cl- as counteranions in complexes 3 and 7 with ortho-positioned dicarboxylate groups, while in complex 1 with dicarboxylate groups in the meta-positions, there is no Cl-. Another interesting feature is that networks of 3, 5-7 still involve the counteranions in the presence of anionic benzenedicarboxylates, and this is indeed quite different from most reported networks containing anionic ligands,2a,10 and only a few examples were reported till now.17 The carboxylate group is not only used as the bridging ligand but also as a counteranion in the construction of MOFs, so the anions of the metal salts usually do not participate in the formation of the complexes.

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Figure 7. Emission spectra of 1 and 3-7 in the solid state at room temperature.

However, in this work, the anions of Zn(II) salts, such as Cl-, NO3-, I-, are joined into the structure with the coexistence of the dicarboxylate groups. The effect of counteranions on the structure of the complexes can be obtained by comparison of 1 and 2, as well as 3-6. Complex 1 obtained from ZnCl2 is a neutral 2D rectangular grid network with (4, 4) topology, while 2 obtained from Zn(NO3)2 · 6H2O under the same reaction conditions is a 3D framework with 2-fold interpenetration. Although no counteranions of Cl- and NO3- appear in the frameworks of 1 and 2 with 1,3-BDC2- as an auxiliary ligand and also as a charge balance, completely different structures of 1 and 2 were obtained. In the case of complexes 3-6 with the same 1,2-BDC2- but different counteranions, 3 and 5, 6 are 3D frameworks, and 4 is 2D network. In complex 3, the chloride coordinated to the Zn(II) atoms, while in 5 and 6, the iodide and nitrate anions did not take part in the coordination and just filled in the 1D channels. As for the complex 4, the acetate anion did not join in the construction of the framework and the dicarboxylate auxiliary ligands also act as counteranions and link the Zn(II) atoms to form Zn4 cluster units. The results imply that the dicarboxylate auxiliary ligands and the counteranions have an important and subtle influence on the structure of the complexes. Photoluminescence Property. Coordination polymers, especially ones with d10 metal centers, have been investigated for fluorescence properties owning to their potential applications in photoactive materials.18 Accordingly, the emission spectra of Zn(II) complexes 1-7, together with those of the ligands tib, 1,2-H2BDC and 1,3-H2BDC, 4-H2BPA were measured in the solid state at room temperature. Emission was observed at 405 nm (λex ) 360 nm) for the free tib ligand, which is same as that reported previously,19 but no obvious luminescence was observed under the same experimental conditions for 1,2H2BDC, 1,3-H2BDC, and 4-H2BPA. It is interesting and to our surprise that only complex 2 did not show clear photoluminescence, while the other complexes exhibit emissions under the experimental conditions. The solid state photoluminescence spectra of complexes 1, 3-7 at room temperature are depicted in Figure 7. It is clear that there are emission bands at 468 nm (λex ) 355 nm) for 1, 416 nm (λex ) 360 nm) for 3, 401 nm (λex ) 360 nm) for 4, 470 nm (λex ) 363 nm) for 5, 459 nm (λex ) 390 nm) for 6, 394 nm (λex ) 358 nm) for 7, respectively. Such emissions of complexes 3, 4 and 7 can be tentatively assigned to the intraligand transition of the tib ligand,20 since a similar emission was observed for the ligand.21 And the emission bands of complexes 1, 5, and 6 are 63, 65, and 54 nm red-shifted, respectively. Such board emission bands

Su et al.

may be tentatively assigned to ligand-to-metal charge transfer (LMCT) as discussed previously.2a In addition, it is noteworthy that complex 1 showed intense emission compared with those of other complexes at room temperature, which may be attributed to the different rigidity of the crystal packing in the solid state.18c,22 This suggests that 1 may be a good candidate for a potential hybrid inorganic-organic photoactive material. The observed blue or red shifts of the emission maximum between the complexes and the tib ligand are considered to mainly originate from the coordination interactions between the metal atom and the ligand.23,24 For further investigation, lowtemperature luminescence measurement was carried out at 77 K. Fortunately, obvious emission was observed at 467 nm (λex ) 355 nm) for 2 (Figure S8, Supporting Information). It is known that lowering the temperature results in the increase of the emission intensity, and the photoluminescence of complex 2 is too weak at room temperature and enhanced at low temperature as reported for the Ag(I) complexes with hexahydropyrimidine derivatives.25 Conclusions Seven new coordination polymers have been successfully isolated under hydrothermal conditions by reactions of tib and varied Zn(II) salts together with benzenedicarbocylate auxiliary ligands. The different structures of 1, 3, and 7 are mainly caused by the different dicarboxylate auxiliary ligands; namely, the different bridging ligand leads to the formation of different frameworks. The different structures of complexes 3, 4, and 5(6) as well as 1 and 2 are ascribed to the different counteranions, implying the impact of counteranion on the formation and structure of the Zn(II) coordination polymers. Moreover, the photoluminescence property of the Zn(II) complexes can be tuned by auxiliary ligands and counteranions. Acknowledgment. This work was financially supported by the National Natural Science Foundation of China (Grant Nos. 20731004 and 20721002) and the National Basic Research Program of China (Grant No. 2007CB925103). Supporting Information Available: X-ray crystallographic file in CIF format, hydrogen bonding data (Table S1), crystal structure and topology (Figures S1-S6), TGA (Figure S7), and luminescence data (Figure S8). This information is available free of charge via the Internet at http://pubs.acs.org.

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CG900059M

Synthesis, Crystal Structure, and Photoluminescence of Coordination

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