Effect of N-Donor Ancillary Ligands on Supramolecular Architectures

Effect of N-Donor Ancillary Ligands on Supramolecular Architectures of a Series of Zinc(II) and Cadmium(II) Complexes with Flexible Tricarboxylate Guang-Xiang Liu,† Yong-Qing Huang,† Qian Chu,† Taka-aki Okamura,‡ Wei-Yin Sun,*,† Hong Liang,*,§ and Norikazu Ueyama‡

CRYSTAL GROWTH & DESIGN 2008 VOL. 8, NO. 9 3233–3245

Coordination Chemistry Institute, State Key Laboratory of Coordination Chemistry, School of Chemistry and Chemical Engineering, Nanjing UniVersity, Nanjing 210093, China, Department of Macromolecular Science, Graduate School of Science, Osaka UniVersity, Toyonaka, Osaka 560-0043, Japan, and School of Chemistry and Chemical Engineering, Guangxi Normal UniVersity, Guilin 541004, China ReceiVed NoVember 18, 2007; ReVised Manuscript ReceiVed May 11, 2008

ABSTRACT: This work presents a systematic investigation on reactions of a flexible tricarboxylic acid with Zn(II), Cd(II) in the presence of varied N-donor ancillary ligands. Seven new metal-organic frameworks [Zn3(bta)2(bpy)2] (1), [Zn3(bta)2(dpe)2] · 2H2O (2), [Zn2(OH)(bta)(bpe)] · 2H2O (3), [Zn2(OH)(bta)(bpp)] (4), [Cd2(bta)(bpy)2(H2O)]ClO4 · H2O (5), [Cd3(bta)2(bpy)2] · 2H2O (6), and [Cd3(bta)2(H2O)2] (7) [bta3- ) benzene-1,3,5-triacetate, bpy ) 4,4′-bipyridine, dpe ) 1,2-di(4-pyridyl)ethylene, bpe ) 1,2-bis(4pyridyl)ethane, and bpp ) 1,3-bis(4-pyridyl)propane] have been obtained and characterized by single-crystal X-ray diffraction, IR, thermogravimetric and elemental analyses. Complexes 1-3, 5, and 6 are three-dimensional (3D) architectures containing infinite two-dimensional (2D) networks pillared by N-donor ligands, whereas 4shows 2D network structure. Complex 3 has 2-fold interpenetration of 3D frameworks with 4.82 networks linked by bpe ligands, and 5 features an unusual 3D cationic supramolecular architecture. Complex 7 contains the Kagome´ lattice inorganic layers, which are further linked by bta3- ligands to form a 3D supramolecular architecture. The results showed that the structure and flexibility of the N-donor ancillary ligands have great influence on the structure of the complexes. The photoluminescence properties of 1-7 in the solid-state at room temperature have been studied. Introduction The aim of contemporary crystal engineering is the development of new crystalline materials with a variety of properties, functions, and possible applications such as separation, magnetism, ion exchange, sensors, catalysis, gas storage, and photoactive materials.1,2 Synthesis and characterization of finite and infinite architectures, using the principle of coordination chemistry, are at the forefront of the investigations with the aim of incorporating physical functions introduced by judicious choice of the metal centers and/or organic ligands. Such kind of metal-organic hybrids also present unique possibilities to combine the properties associated with the individual components of the organic and inorganic in one compound with the consequent aim of controlling the communication between the individual properties.3–5 It is known that many factors, such as the coordination geometry of the central metal ions and counterions, as well as the synthetic method, have influence on the desirable metal-organic frameworks (MOFs).6–8 Particularly, the organic ligands play crucial roles in determining the resulted polymeric structures, because the change in the type of bridging units, the flexibility of the molecular backbone, conformational preference, and symmetry of organic ligands can result in a remarkable class of materials bearing diverse architectures and functions.9 Therefore, the prospect of tuning the properties of MOFs through change of organic ligands provides an impetus for further research on metal-organic supramolecular architectures.10 * Corresponding Author: Dr. Wei-Yin Sun, Mailing Address: Coordination Chemistry Institute, Nanjing University, Nanjing 210093, China. Telephone: +86-25-83593485. Fax:+86-25-83314502. E-mail: [email protected]. † Nanjing University. ‡ Osaka University. § Guangxi Normal University.

One of our interests is the study of MOFs with carboxylate ligands due to their excellent coordination capability and the possibility of offering new functional materials. Compared to the rigid carboxylate ligands, the flexible ones have been investigated limitedly so far, possibly due to the difficulties in predicting the resulted framework structure.11,12 On the other hand, N-donor ligands with certain spacers between the two terminal coordination groups, for example 4,4-bipyridine (bpy),13 1,2-bis(4-pyridyl)ethane (bpe),14 1,2-di(4-pyridyl)ethylene (dpe),15 and 1,3-bi(4-pyridyl)propane (bpp),16 can be used as ancillary ligand together with the carboxylate ligand to meet the requirement of coordination geometries of metal ions in the assembly process. Such N-donor ligands are good candidates to produce unique structural motifs with beautiful aesthetics and useful functional properties. To gain more information about the coordination chemistry of flexible carboxylate complexes, we focus our attention on the construction of novel MOFs by using flexible carboxylate ligand, e.g. benzene-1,3,5-triacetate (bta3-), in our laboratory,17 and the results showed that a great variety of polymeric structures can be obtained as a result of the different conformations (e.g., syn,syn,syn and syn,anti,anti) and coordination modes of the bta3- ligand (Scheme S1, Supporting Information). Herein we report on seven new coordination polymers, namely [Zn3(bta)2(bpy)2] (1), [Zn3(bta)2(dpe)2] · 2H2O (2), [Zn2(OH)(bta)(bpe)] · 2H2O (3), [Zn2(OH)(bta)(bpp)] (4), [Cd2(bta)(bpy)2(H2O)]ClO4 · H2O (5), [Cd3(bta)2(bpy)2] · 2H2O (6), and [Cd3(bta)2(H2O)2] · (7), which were constructed by zinc(II) and cadmium(II) salts with benzene-1,3,5-triacetate and N-donor ligands. Experimental Section All commercially available chemicals are of reagent grade and used as received without further purification. The compound benzene-1,3,5-

10.1021/cg701137d CCC: $40.75  2008 American Chemical Society Published on Web 07/17/2008

3234 Crystal Growth & Design, Vol. 8, No. 9, 2008

Liu et al.

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

Empirical formula Formula weight Crystal system Space group a /Å b /Å c /Å R /° β /° γ /° V (Å3) Z Dc (g cm-3) µ (mm-1) F(000) 2θmax /° Reflns. collected Independent reflns. Rint Parameters refined Goodness-of-fit R1a (I > 2σ (I)) wR2b (I > 2σ (I)) R1a (all data) wR2b (all data) ∆Fmin and ∆Fmax (e/Å3) a

1

2

3

4

5

6

7

C44H34N4O12Zn3 1006.86 monoclinic P21/c 11.626(3) 11.192(3) 15.631(4) 90 110.536(5) 90 1904.6(9) 2 1.756 1.951 1024 1.87-25.99 9936 3721 0.0542 286 1.004 0.0338 0.0799 0.0413 0.0822 0.458, -0.384

C48H42N4O14Zn3 1094.97 triclinic P1j 9.6558(12) 9.8429(12) 13.4437(16) 105.134(2) 104.420(2) 104.882(2) 1121.5(2) 1 1.621 1.667 506 1.67-25.00 5637 3883 0.0331 313 1.089 0.0734 0.1524 0.1010 0.1657 0.816, -0.359

C24H26N2O9Zn2 617.21 Monoclinic P21/c 10.4037(9) 15.0027(13) 16.8420(14) 90 106.460(2) 90 2521.0(4) 4 1.626 1.959 1264 1.85-27.00 14276 5481 0.0239 354 1.070 0.0332 0.0895 0.0406 0.0924 0.479, -0.246

C25H24N2O7Zn2 595.20 triclinic P1j 9.2710(11) 10.4023(12) 14.4362(17) 71.676(2) 81.677(2) 66.020(2) 1207.3(2) 2 1.637 2.036 608 2.31-25.00 6021 4168 0.0182 329 1.052 0.0345 0.0867 0.0405 0.0892 0.478, -0.281

C32H29 N4O12ClCd2 921.84 monoclinic P21/n 12.441(2) 15.431(3) 18.068(3) 90 98.272(4) 90 3432.6(11) 4 1.784 1.386 1832 1.74-26.00 6725 4188 0.0601 497 0.890 0.0545 0.0943 0.0998 0.1063 1.139, -0.492

C44H38N4O14Cd3 1183.98 triclinic P1j 9.4888 (16) 9.7903 (15) 12.949 (2) 71.607(4) 68.933(4) 78.040(4) 1059.2(3) 1 1.856 1.568 586 3.02-25.00 3724 3226 0.0576 295 1.169 0.0934 0.2915 0.1046 0.2955 3.421, -1.903

C24H22O14Cd3 871.62 Monoclinic P21/c 11.0178(16) 13.8102(19) 9.0227(13) 90 107.476(2) 90 1309.5(3) 2 2.211 2.487 844 2.44-25.50 6687 2414 0.0789 187 1.003 0.0384 0.0762 0.0501 0.0792 0.822, -0.728

R )Σ|Fo| - |Fc|/Σ|Fo|. b Rw ) |Σw(|Fo|2 - |Fc|2)|/Σ|w(Fo)2|1/2, w ) 1/[σ2(Fo2) + (aP)2 + bP], P ) (Fo2 + 2Fc2)/3.

triacetic acid (H3bta) was prepared by the method reported in the literature.18 Solvents were purified according to the standard methods. C, H, and N analyses were made on a Perkin-Elmer 240C elemental analyzer. Infrared (IR) spectra were recorded on a Bruker Vector22 FT-IR spectrophotometer by using KBr discs. Thermogravimetric analyses were performed on a simultaneous SDT 2960 thermal analyzer under nitrogen with a heating rate of 10 °C min-1. The luminescent spectra for the solid samples were recorded at the room temperature on an Aminco Bowman Series 2 spectrophotometer with xenon arc lamp as the light source. In the measurements of the emission and excitation spectra, the pass width was 5.0 nm. Synthesis of [Zn3(bta)2(bpy)2] (1). A mixture of H3bta (0.1 mmol), Zn(NO3)2 · 6H2O (0.15 mmol), bpy (0.1 mmol) and 10 mL of deionized water was placed in a Teflon-lined stainless vessel (18 mL), and 0.3 mL of pyridine was added while stirring. The vessel was then sealed and heated to 180 °C for 72 h under autogenous pressure and then cooled slowly to the room temperature. Yellow crystals suitable for single-crystal X-ray diffraction analysis were collected by filtration, washed with deionized water and ethanol, and dried in air at room temperature. Yield: 70%. Anal. Calcd for C44H34N4O12Zn3: C, 52.48; H, 3.40; N, 5.56%; Found: C, 52.44; H, 3.44; N, 5.58%. IR (KBr pellet, cm-1): 3431 (w), 2959 (w), 1611(m), 1587 (s), 1559 (m), 1419 (m), 1386 (s), 1322 (w), 1284 (w), 1219 (w), 1175 (w), 1070 (w), 1046 (w), 812 (w), 637 (w), 569 (w). Synthesis of [Zn3(bta)2(dpe)2] · 2H2O (2). A mixture containing Zn(NO3)2 · 6H2O (0.1 mmol), dpe (0.1 mmol), H3bta (0.1 mmol), NaOH (0.3 mmol) in 10 mL H2O was sealed in a 18 mL Teflon lined stainless steel container and heated at 160 °C for 72 h. Colorless block crystals of 2 were collected by filtration with a field of 67%. Anal. Calcd for C48H42N4O14Zn3: C, 52.64; H, 3.87; N, 5.12%. Found: C, 52.61; H, 3.93; N, 5.11%. IR (KBr pellet): 3421 (w), 2966 (w), 1614(m), 1583 (s), 1549 (m), 1422 (m), 1387 (s), 1317 (w), 1287 (w), 1217(w), 1182 (w), 1088 (w), 1055 (w), 822 (w), 651 (w), 567 (w). Synthesis of [Zn2(OH)(bta)(bpe)] · 2H2O (3). A mixture of H3bta (0.1 mmol), Zn(NO3)2 · 6H2O (0.10 mmol), bpe (0.1 mmol) and 10 mL of deionized water was placed in a Teflon-lined stainless vessel (18 mL) and 0.6 mL of a 0.50 M aqueous NaOH solution was added while stirring. The vessel was then sealed and heated to 140 °C for 72 h under autogenous pressure and then cooled slowly to room temperature. Yellow block crystals were collected by filtration, washed with deionized water and ethanol, and dried in air at room temperature. Yield: 81%. Anal. Calcd for C24H26N2O9Zn2: C, 46.70; H, 4.25; N, 4.54%; Found: C, 46.68; H, 4.30; N, 4.57%. IR (KBr pellet, cm-1): 3671 (s), 3462 (m), 2907 (w), 1618 (m), 1554 (s), 1438 (s), 1390 (m), 1321(w),

1285 (w), 1258 (w), 1174 (w), 1028 (w), 948 (w), 836 (w), 817 (w), 762 (w), 652 (w), 561 (w). Synthesis of [Zn2(OH)(bta)(bpp)] (4). A mixture of Zn(NO3)2 · 6H2O (0.15 mmol), H3bta (0.1 mmol), bpp (0.1 mmol), NaOH (0.3 mmol) and H2O (8 mL) was sealed in a 18 mL Teflon lined stainless steel container and heated at 140 °C for 72 h. Paleyellow block crystals were collected and dried in air at room temperature. Yield: 81%. Anal. Calcd for C25H24N2O7Zn2: C, 50.44; H, 4.06; N, 4.71%. Found: C, 50.42; H, 4.02; N, 4.75%. IR (KBr pellet, cm-1): 3651(s), 3452 (m), 2908 (w), 1609 (m), 1583 (s), 1548 (m), 1426(m), 1385 (s), 1323(w), 1285 (w), 1252 (w), 1177 (w), 1018 (w), 945(w), 837 (w), 823 (w), 755(w), 632 (w), 565 (w). Synthesis of [Cd2(bta)(bpy)2(H2O)]ClO4 · H2O (5). A mixture of H3bta (0.1 mmol), Cd(ClO4)2 · 6H2O (0.15 mmol), bpy (0.1 mmol) and 10 mL of deionized water was placed in a Teflon-lined stainless vessel (18 mL), and 0.3 mL of pyridine was added while stirring. The vessel was then sealed and heated to 180 °C for 72 h under autogenous pressure, and then cooled slowly to room temperature. Light-yellow crystals were collected with a yield of 64%. Anal. Calcd for C32H29N4O12ClCd2: C, 41.69; H, 3.17; N, 6.08%; Found: C, 41.65; H, 3.24; N, 6.05%. IR (KBr pellet, cm-1): 3421 (m), 2920 (w), 1605 (m), 1563 (s), 1415 (m), 1397 (s), 1278 (w), 1221 (w), 1100 (s), 1007 (w), 945 (w), 919 (w), 813 (m), 750 (m), 696 (w), 630 (m), 582 (m). Synthesis of [Cd3(bta)2(bpy)2] · 2H2O (6). The title complex was obtained by the same procedure as that for 5, except that Cd(NO3)2 · 4H2O (0.15 mmol), instead of Cd(ClO4)2 · 6H2O, was used. Yellow pillar crystals were obtained. Yield: 46%. Anal. Calcd for C44H38N4O14Cd3: C, 44.63; H, 3.23; N, 4.73%; Found: C, 44.65; H, 3.31; N, 4.67%. IR (KBr pellet, cm-1): 3451 (m), 2953 (w), 1610 (w), 1592 (s), 1428 (m), 1392 (m), 1322 (w), 1261 (m), 1244 (w), 1174 (w), 1024 (w), 927 (w), 834 (w), 812(w), 742(w), 657(w), 554 (w). Synthesis of [Cd3(bta)2(H2O)2] (7). A mixture containing Cd(NO3)2 · 6H2O (0.15 mmol), phen (0.1 mmol), H3bta (0.1 mmol), NaOH (0.3 mmol) dissolved in water and ethanol (10 mL, v/v ) 3:1) was sealed in a 18 mL Teflon lined stainless steel container and heated at 160 °C for 120 h. Pale-yellow platelet crystals of 7 were collected by filtration and washed by water and ethanol several times with yield of 72%. Anal. Calcd for C24H22O14Cd3: C, 33.07; H, 2.54%. Found: C, 33.05; H, 2.57%. IR (KBr pellet): 3382 (br), 2925 (w), 1635 (m), 1574 (s), 1438 (m), 1383 (s), 1274 (w), 1170 (w), 1154 (w), 1015 (w), 906 (w), 812 (w), 771 (m), 725 (m), 689 (w), 589 (w). Crystallography. The crystallographic data collections for complexes 1-5 and 7 were carried out on a Bruker Smart Apex CCD with

Zn(II), Cd(II) Complexes with Flexible Tricarboxylate

Crystal Growth & Design, Vol. 8, No. 9, 2008 3235

Table 2. Selected Bond Distances [Å] and Angles [deg] for Complexes 1-7a 1 Zn(1)-O(1)#1 Zn(1)-O(6) Zn(2)-O(5) Zn(2)-N(2)#5 O(1)#1-Zn(1)-O(4)#2 O(4)#2-Zn(1)-O(6) O(4)#2-Zn(1)-N(1) O(5)-Zn(2)-N(2)#5 O(2)#1-Zn(2)-N(2)#5 O(2)#1-Zn(2)-N(2)#6 O(5)#3-Zn(2)-O(2)#1 O(5)-Zn(2)-N(2)#6

1.9367(17) 1.9744(19) 2.1131(18) 2.126(2) 109.29(8) 103.65(8) 112.34(9) 86.54(8) 88.00(7) 92.00(7) 86.90(7) 93.46(8)

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

2.047(4) 2.255(4) 1.984(5) 2.075(5) 87.9(2) 180.0(3) 90.84(18) 90.93(16) 89.16(18) 97.3(2) 103.0(2) 108.49(19) 161.30(19) 91.4(2)

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

1.9117(18) 1.9894(17) 1.9112(18) 1.9942(16) 120.48(8) 109.94(8) 101.35(7) 123.51(8) 112.77(8) 97.12(7)

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

1.885(2) 2.008(2) 1.897(2) 2.016(2) 2.428(2) 120.37(10) 101.17(9) 106.74(9) 101.96(10) 98.08(8) 100.16(10) 97.97(9) 57.49(8)

Cd(1)-O(7) Cd(1)-O(4) Cd(1)-N(3)#2 Cd(2)-N(1)#2 Cd(2)-O(1)#3 Cd(2)-O(6)#4 Cd(2)-O(5)#4 O(7)-Cd(1)-O(5)#1 O(5)#1-Cd(1)-O(4) O(5)#1-Cd(1)-N(2) O(7)-Cd(1)-N(3)#2 O(4)-Cd(1)-N(3)#2 O(7)-Cd(1)-O(3) O(4)-Cd(1)-O(3) N(3)#2-Cd(1)-O(3) N(1)#2-Cd(2)-O(1)#3 N(1)#2-Cd(2)-O(3) O(1)#3-Cd(2)-O(3)

2.200(5) 2.263(4) 2.346(5) 2.296(5) 2.338(5) 2.392(4) 2.586(4) 95.04(17) 115.02(16) 91.9(2) 95.5(2) 89.59(18) 96.01(17) 54.54(15) 87.47(17) 92.9(2) 91.47(18) 145.88(15)

Zn(1)-O(4)#2 Zn(1)-N(1) Zn(2)-O(2)#1

1.9499(19) 2.057(2) 2.1197(17)

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

111.22(8) 112.34(8) 107.66(8) 93.10(7) 180.00(7) 180.0 180.00(8)

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

2.092(5) 1.965(4) 2.064(4) 2.315(5) 180.0(2) 89.07(16) 92.1(2) 180.0(2) 102.49(18) 139.08(18) 99.6(2) 94.95(19) 59.38(16)

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

1.9381(16) 2.0333(18) 1.9283(16) 2.0650(18) 111.73(7) 109.72(8) 101.43(8) 106.38(8) 112.95(8) 101.97(7)

Zn(1)-O(6)#1 Zn(1)-N(2) Zn(2)-O(2) Zn(2)-N(1)

1.952(2) 2.033(2) 2.005(2) 2.041(3)

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

101.06(10) 122.44(10) 100.19(9) 125.19(10) 111.21(10) 114.57(9) 154.83(8) 86.62(9)

Cd(1)-O(5)#1 Cd(1)-N(2) Cd(1)-O(3) Cd(2)-N(4) Cd(2)-O(3) Cd(2)-O(2)#3

2.236(5) 2.327(6) 2.497(4) 2.313(5) 2.346(5) 2.426(5)

O(7)-Cd(1)-O(4) O(7)-Cd(1)-N(2) O(4)-Cd(1)-N(2) O(5)#1-Cd(1)-N(3)#2 N(2)-Cd(1)-N(3)#2 O(5)#1-Cd(1)-O(3) N(2)-Cd(1)-O(3) N(1)#2-Cd(2)-N(4) N(4)-Cd(2)-O(1)#3 N(4)-Cd(2)-O(3) N(1)#2-Cd(2)-O(6)#4

149.92(19) 88.8(2) 89.21(18) 82.57(18) 173.2(2) 165.77(14) 97.24(19) 172.9(2) 92.21(19) 87.00(18) 88.52(18)

2

3

4

5


Liu et al. Table 2. Continued

N(4)-Cd(2)-O(6)#4 O(3)-Cd(2)-O(6)#4 N(4)-Cd(2)-O(2)#3 O(3)-Cd(2)-O(2)#3 N(1)#2-Cd(2)-O(5)#4 O(1)#3-Cd(2)-O(5)#4 O(6)#4-Cd(2)-O(5)#4

84.51(17) 86.37(15) 89.43(19) 91.80(16) 79.84(16) 77.08(15) 51.61(14)

Cd(1)-O(3)#1 Cd(1)-O(5)#4 Cd(2)-O(4)#6 Cd(2)-O(2) Cd(2)-O(1) O(3)#1-Cd(1)-N(1) N(1)-Cd(1)-O(5)#4 N(1)-Cd(1)-N(1)#3 O(3)#2-Cd(1)-N(1) O(3)#2-Cd(1)-O(5)#4 O(4)#6-Cd(2)-N(2) N(2)-Cd(2)-O(2) N(2)-Cd(2)-O(5)#7 O(4)#6-Cd(2)-O(1) O(2)-Cd(2)-O(1) O(4)#6-Cd(2)-O(6)#7 O(2)-Cd(2)-O(6)#7

2.245(15) 2.316(12) 2.233(13) 2.322(14) 2.368(14) 94.0(6) 91.6(5) 180.0 86.0(6) 88.7(5) 93.8(6) 148.0(5) 107.7(5) 99.8(5) 55.9(5) 160.4(5) 98.2(5)

Cd(1)-O(1W) Cd(1)-O(3)#2 Cd(2)-O(4)#4 Cd(2)-O(2)#6 Cd(2)-O(5)#5 O(1W)-Cd(1)-O(1) O(1)-Cd(1)-O(3)#2 O(1)#1-Cd(1)-O(1) O(1)#1-Cd(1)-O(3)#2 O(1W)#1-Cd(1)-O(1)#1 O(4)#4-Cd(2)-O(6)#5 O(6)#5-Cd(2)-O(5) O(6)#5-Cd(2)-O(2)#6 O(4)#4-Cd(2)-O(1)#6 O(5)-Cd(2)-O(1)#6 O(4)#4-Cd(2)-O(5)#5 O(5)-Cd(2)-O(5)#5

2.202(3) 2.301(4) 2.213(3) 2.275(3) 2.609(4) 89.08(14) 99.42(14) 180.0(2) 80.57(14) 89.08(14) 115.68(13) 127.44(14) 84.66(13) 98.47(12) 99.68(13) 99.85(13) 171.62(15)

O(1)#3-Cd(2)-O(6)#4 N(1)#2-Cd(2)-O(2)#3 O(1)#3-Cd(2)-O(2)#3 O(6)#4-Cd(2)-O(2)#3 N(4)-Cd(2)-O(5)#4 O(3)-Cd(2)-O(5)#4 O(2)#3-Cd(2)-O(5)#4

127.55(15) 97.51(19) 54.07(16) 173.74(15) 96.60(17) 136.92(15) 131.01(16)

Cd(1)-N(1)

2.281(15)

Cd(2)-N(2) Cd(2)-O(5)#7 Cd(2)-O(6)#7 O(3)#1-Cd(1)-O(5)#4 O(3)#1-Cd(1)-O(3)#2 O(5)#4-Cd(1)-O(5)#5 N(1)-Cd(1)-O(5)#5 O(1)-Cd(2)-O(6)#7 O(4)#6-Cd(2)-O(2) O(4)#6-Cd(2)-O(5)#7 O(2)-Cd(2)-O(5)#7 N(2)-Cd(2)-O(1) O(5)#7-Cd(2)-O(1) N(2)-Cd(2)-O(6)#7 O(5)#7-Cd(2)-O(6)#7

2.298(16) 2.333(12) 2.389(13) 91.3(5) 180.0 180.0 88.4(5) 99.2(5) 88.5(6) 105.5(5) 102.4(5) 92.4(5) 146.2(5) 90.3(5) 55.1(4)

Cd(1)-O(1) Cd(2)-O(5) Cd(2)-O(6)#5 Cd(2)-O(1)#6

2.292(4) 2.269(4) 2.254(3) 2.429(3)

O(1W)-Cd(1)-O(3)#2 O(1W)#1-Cd(1)-O(1W) O(3)#2-Cd(1)-O(3)#3 O(1W)#1-Cd(1)-O(3)#2 O(1)#6-Cd(2)-O(5)#5 O(4)#4-Cd(2)-O(5) O(4)#4-Cd(2)-O(2)#6 O(5)-Cd(2)-O(2)#6 O(6)#5-Cd(2)-O(1)#6 O(2)#6-Cd(2)-O(1)#6 O(6)#5-Cd(2)-O(5)#5 O(2)#6-Cd(2)-O(5)#5

91.81(14) 179.999(1) 179.999(1) 88.19(14) 75.39(12) 87.49(13) 153.17(13) 93.56(13) 120.38(13) 54.90(12) 52.69(12) 78.06(13)

6

7

a Symmetry transformation used to generate equivalent atoms: #1 x, y+1, z; #2 x, -y+1/2, z-1/2; #3 -x+2, -y+1, -z+1; #4 -x+2, -y, -z+1; #5 -x+1, -y+1, -z+1; #6 x+1, y, z for 1; #1 -x, y, z; #2 x, y+1, z+1; #3 -x, -y-1, -z-1; #4 x-1, y-1, z; #5 -x+1, -y+1, -z; #6 x-1, y, z for 2; #1 x-1, -y+3/2, z-1/2; #2 -x+1, -y+2, -z; #3 x+1, -y+3/2, z-1/2 for 3; #1 x-1, y+1, z; #2 -x, -y, -z+1 for 4; #1 -x, -y+1, -z+2; #2 x-1/ 2, -y+3/2, z+1/2; #3 -x, -y+2, -z+2; #4 x-1/2, -y+3/2, z-1/2 for 5; #1 -x+1, -y, -z+1; #2 x-1, y, z-1; #3 -x, -y, -z; #4 -x, -y+1, -z+1; #5 x, y-1, z-1; #6 x-1, y, z; #7 x, y-1, z for 6; #1: -x+2, -y+2, -z+2; #2: -x+1, y+1/2, -z+3/2; #3: x+1, -y+3/2, z+1/2; #4: -x, -y+2, -z+1; #5: x, -y+5/2, z-1/2; #6: -x+1, -y+2, -z+1 for 7.

graphite-monochromated Mo KR radiation (λ ) 0.71073 Å) at 293(2) K using the ω-scan technique. The data were integrated by using the SAINT program,19 which also did the intensity correction for Lorentz and polarization effect. An empirical absorption correction was applied using the SADABS program.20 The data collection for complex 6 was carried out on a Rigaku RAXIS-RAPID Imaging Plate diffractometer with graphite-monochromated Mo KR radiation (λ ) 0.71075 Å) at 200 K using the ω-scan technique. Absorption correct was applied using the program ABSCOR.21 The structures were solved by direct methods using SHELXS-97 and all non-hydrogen atoms were refined anisotropically on F2 by the full-matrix least-squares technique.22,23 The hydrogen atoms except for those of water molecules and hydroxyl groups were generated geometrically. All calculations were performed on a personal computer with the SHELXL-97 crystallographic software package.23 Atoms Cl1, O8, O9, O10, O11 in complex 5 disordered into two positions with the site occupancy factors of 0.508(14) and 0.492(14), respectively. The details of the crystal parameters, data collection and refinement for complexes are summarized in Table 1, and selected bond lengths and angles with their estimated standard

deviations are listed in Table 2. Further details are provided in the Supporting Information.

Results and Discussion Synthesis of the Complexes. The mixture of metal salt and H3bta with N-donor ligand usually results in precipitation in aqueous solution, which makes it difficult to grow crystals of the complex. The hydrothermal method has been extensively explored as an effective and powerful tool in the self-assembly of MOFs, especially for high-dimensional frameworks. Therefore, complexes 1-7 were synthesized under hydrothermal conditions. In addition, pyridine or NaOH was used to neutralize the triacid. All the carboxyl groups of the H3bta in 1-7 were found to be deprotonated as evidenced by IR spectral data (see Experimental section and below) and the results of crystallographic analysis (vide post). Although the seven complexes were synthesized in similar way, there are differences in the coordination modes of bta3- and N-donor ligands, which exert



Figure 1. (a) ORTEP representation of complex 1 showing the local coordination environment of Zn(II) with thermal ellipsoids at the 30% level of probability. All hydrogen atoms are omitted for clarity. Top (b) and side (c) views of the 2D network of 1 with trimetallic units linked by bta3ligands. (d) 3D supramolecular structure of complex 1 pillared by bpy ligands.

an important influence on the structure of the supramolecular architectures reflected by the unique structural features of the complexes as described below. FT-IR Spectra and Thermogravimetric Analyses. The IR spectral data show features attributable to the carboxylate stretching vibrations of the complexes. The absence of bands in the range of 1760-1680 cm-1 indicates the complete deprotonation of the H3bta ligand. The characteristic bands of the carboxylate groups appear in the range 1550-1620 cm-1 for the asymmetric stretching and 1370-1490 cm-1 for the symmetric stretching. The broadband at ca. 3300 cm-1 correspond to the vibration of the water in the complexes 2, 3, 5, 6, and 7. The IR spectra of complexes 3 and 4 contain characteristic peaks of hydroxyl group at 3671 and 3651 cm-1, respectively. The IR spectrum of 5 exhibited characteristic band of perchlorate anion at 1092 cm-1. Thermogravimetric analyses (TGA) were carried out for the synthesized complexes except for 5 with perchlorate, and the results of the TGA are shown in Figure S1 (Supporting Information). Complex 1 is stable up to ca. 400 °C, and above the temperature, the decomposition of the complex starts. A weight loss of 3.42% below 150 °C (calcd 3.29%) was observed for 2, due to the loss of lattice water molecules. Then the framework begins to decompose from ca. 380 °C. For 3, a weight loss of 6.01% below 130 °C (calcd 5.84%) is attributed to loss of uncoordinated water molecules. Further weight loss

was found from ca. 290 °C for 3 due to the decomposition of the framework. Complex 4 is stable up to ca. 210 °C, where the decomposition starts. Complex 6 has similar weight loss and decomposition process as those of 2 and 3, a weight loss of 4.11% below 180 °C (calcd 3.05%) corresponds to the loss of uncoordinated water molecules. The residue begins to decompose from ca. 280 °C. As for 7, the first weight loss of 4.00% (calculated: 4.13%) in the range of 138-256 °C reveals the exclusion of two coordinated water molecules, then began to decompose upon further heating. Description of Crystal Structures. Complex [Zn3(bta)2(bpy)2] 1. The X-ray crystallographic analysis revealed that 1 is a 3D supramolecular architecture with infinite 2D [Zn3(bta)2] networks pillared by rod-like bpy ligands. As depicted in Figure 1a, there are two Zn(II) atoms with different coordination environments in the asymmetric unit of 1. The Zn1 is four coordinated with tetrahedral coordination geometry defined by one nitrogen donor from bpy and three oxygen atoms from three different bta3- ligands, whereas the Zn2 center is situated at an inversion center and has an octahedral coordination environment surrounded by four oxygen atoms from four different carboxylate groups forming the basal plane and two nitrogen donors from two different bpy occupying the apical positions. The Zn1 and Zn2 atoms are double bridged by two carboxylate groups with Zn1 · · · Zn2 separation of 4.12 Å to form a dinuclear unit, which is further interconnected by another Zn1 through another


Liu et al.

Figure 2. (a) ORTEP representation of complex 2 showing the local coordination environment of Zn(II) with thermal ellipsoids at the 30% level of probability. All hydrogen atoms and water molecules are omitted for clarity. Top (b) and side (c) views of 2D network of complex 2. (d) 3D structure of 2 with lattice water molecules represented by red balls.

two carboxylate bridges to form a trimetallic moiety (Figure 1b). Such trimetallic units are linked by bta3- ligands to generate a 2D network (Figure 1b and c). Each bta3- ligand acts as a µ5-bridge connecting five Zn(II) atoms (Scheme S1a, Supporting Information), in which one carboxylate group adopts a monodentate mode coordinating to one zinc atom, while each of the other two carboxylate groups adopts a µ2-η1:η1 bridging mode coordinating with two zinc atoms. The 2D networks are further pillared by rod-like bpy ligands to form a 3D supramolecular architecture with Zn · · · Zn separation of 11.26 Å linked by bpy (Figure 1d). There are face-to-face π-π interactions between the pyridine ring planes of bpy with a centroid-centroid separation of 3.86 Å in complex 1. Crystal Structure of [Zn3(bta)2(dpe)2] · 2H2O 2. When dpe N-donor ligand with a rigid -CHdCH- spacer between two terminal pyridyl groups, instead of the rod-like bpy, was incorporated into the reaction of H3bta with zinc nitrate, complex 2 was isolated. As shown in Figure 2a, there are two unique Zn(II) centers with different coordination geometries in the asymmetric unit. The Zn1 in 2 is located at an inversion center with an octahedral coordination environment, which is similar to the Zn2 in 1. Six coordination atoms around Zn1 are two nitrogen donors from two different dpe and four carboxylate oxygen atoms from four different bta3- ligands. The Zn2 center is coordinated by one nitrogen atom from dpe and the additional positions are occupied by four oxygen atoms from three different bta3- ligands. The Zn2-O bond distances range from 1.965(4)

to 2.315(5) Å, and O-Zn2-O bond angles are in the range of 59.38(16)-161.30(19)° as listed in Table 2. The local coordination geometry around Zn2 in 2 can be described as a distorted square pyramid with NO4 donor set,25 which is different from the Zn1 in 1 with tetrahedral coordination geometry. The nitrogen atom from dpe occupies the apical position and four oxygen atoms form the basal plane. The remarkable difference between 1 and 2 is the coordination mode of bta3- ligand. Each bta3- ligand in 2 acts as a µ5-bridge linking five zinc(II) atoms (Scheme S1b, Supporting Information), in which one carboxylate group adopts a monodentate mode coordinating to one zinc atom, another carboxylate group adopts a µ2-η1:η1 bridging coordination mode connecting two zinc atoms, while the third carboxylate group adopts a µ2-η2: η1 bridging coordination mode connecting two zinc atoms. Such linkage mode of bta3- ligand makes 2 a 2D network structure without consideration of dpe as illustrated in Figure 2b and c, in which there are also Zn2-Zn1-Zn2 trinuclear units double bridged by two carboxylate groups between Zn1 and Zn2 with Zn1 · · · Zn2 distance of 3.71 Å. Progression of the 2D networks through dpe bridges yields a 3D supramolecular structure (Figure 2d) with Zn · · · Zn separation of 13.49 Å linked by dpe. In complex 2, there are also face-to-face π-π interactions between the pyridine ring planes of dpe with centroid-centroid distance of 3.61 Å. Uncoordinated water molecules in 2 occupy the vacancy between the 2D layers



Figure 3. (a) ORTEP representation of complex 3 showing the local coordination environment of Zn(II) with thermal ellipsoids at the 30% level of probability. All hydrogen atoms and water molecule are omitted for clarity. (b) 2D network in complex 3 with 4.82 topology. (c) Topological view of the 2D network in complex 3. The purple circles represent binuclear zinc(II) units and the yellow circles represent the center of the benzene ring of bta3-. (d) 3D structure of 3 in which the water molecules were omitted for clarity. (e) Space-filling view of the 2-fold interpenetrated 3D structure of complex 3.

linked by dpe. However, no such lattice water molecules were observed in 1, probably due to the short pillared bpy ligand. Crystal Structure of [Zn2(OH)(bta)(bpe)] · 2H2O 3. It is interesting to find that when bpe ligand with a more flexible spacer -CH2-CH2- between two pyridyl groups was introduced in the reaction of zinc nitrate with H3bta, complex 3 with total different structure was obtained. Single-crystal X-ray diffraction analysis revealed that 3 is a 3D framework with 2-fold interpenetration. As shown in Figure 3a, there are two crystallographically independent Zn(II) atoms in the repeat unit of 3 bridged by OH- group. In addition to the hydroxyl bridge, each Zn(II) center is coordinated by one nitrogen atom from bpe and two carboxylate oxygen atoms from two different bta3ligands; hence, the Zn(II) atom is four coordinated with distorted tetrahedral geometry. The Zn1 and Zn2 atoms with Zn1 · · · Zn2 separation of 3.16 Å are bridged by a carboxylate, and the hydroxyl groups to form a dinuclear unit, which is further linked through the bta3- ligands to generate a 2D network (Figure 3b). Each bta3- ligand in 3 acts as a µ4-bridge, rather than µ5-bridge as observed in 1 and 2, to link four zinc atoms (Scheme S1c, Supporting Information), since one carboxylate group adopts a µ2-η1:η1 bridging coordination mode connecting two zinc atoms,

and each of the other two carboxylate groups adopts a monodentate mode coordinating to one zinc atom. If the centers of the dinuclear unit and the benzene ring of the bta3- ligand are considered as nodes, the 2D network of 3 shown in Figure 3b has 4.82 topology, which can be seen clearly from simplified drawing exhibited in Figure 3c. The 2D layer structures are further connected by bpe ligands to form a 3D architecture (Figure 3d). The separation of the Zn · · · Zn bridged by bpe ligand is 13.34 Å, which is certainly longer than that in 1 linked by bpy, but is similar to that in 2 connected by dpe. The bpe ligand has an anticonformation, and the dihedral angle between the two terminal pyridine rings is 47.08°, which is lager than that in dpe (3.26°) in 2. It is noticeable that the 3D framework pillared by bpe ligands has large vacancy to allow not only the presence of uncoordinated water molecules as that in 2, but also the inclusion of another 3D framework. Therefore, the remarkable structure feature of complex 3 is 2-fold interpenetration of the 3D framework (Figure 3e). The results show that the structure and flexibility of the N-donor ligands have great influence on the structure of the complexes.


Figure 4. (a) ORTEP representation of complex 4 showing the local coordination environment of Zn(II) with thermal ellipsoids at the 30% level of probability. All hydrogen atoms are omitted for clarity. (b) 1D chain structure in complex 4 formed by Zn(II) and bta3-. (c) Top view of the 2D network structure of complex 4. Blue solid lines represent the bpp ligands.

Crystal Structure of [Zn2(OH)(bta)(bpp)] 4. When the spacer between the two terminal pyridyl groups extends from -CH2-CH2- in bpe to -CH2-CH2-CH2- in bpp, complex 4 with bpp ligand showed different structure from that of 3 with bpe. Complex 4 crystallizes in the triclinic with space group P1j, rather than in monoclinic with space group P21/c as observed in 3 (Table 1). The coordination environment of the metal atoms and the coordination mode of bta3- ligand are shown in Figure 4a and Scheme S1d (Supporting Information), respectively. The Zn1 atom is coordinated by one nitrogen atom of bpp, one hydroxyl oxygen atom and two carboxylate oxygen atoms of two different bta3- ligands with distorted tetrahedral coordination geometry. The bond lengths of Zn1-N1, Zn1-O1, Zn1-O7, and Zn1-O6A are 2.033(2), 2.008(2), 1.885(2), and 1.952(2) Å (Table 2), respectively, which are the typical distances of Zn-N and Zn-O bonds. The Zn2 atom is coordinated by one nitrogen atom of bpp, one hydroxyl oxygen atom and three carboxylate oxygen atoms from two different bta3- ligands in a distorted square pyramid environment,24 in

Liu et al.

which the nitrogen atom occupies the apical positions and four oxygen atoms form the basal plane. The Zn1 and Zn2 atoms are bridged by a carboxylate group and a hydroxyl group with Zn1 · · · Zn2 separation of 3.21 Å to form a dinuclear unit, which is similar to that observed in 3 as mentioned above. However, the dinuclear units in 4 are connected through the bta3- ligands to generate an infinite 1D chain (Figure 4b), while in the case of 3, the dinuclear units are linked together by bta3- to form 2D network (Figure 3b). Each bta3- ligand acts as a µ4-bridge linking four zinc atoms, in which one carboxylate group adopts a µ2-η1:η1 bridging coordination mode connecting two zinc atoms, while the other two carboxylate groups adopt a monodentate mode and a µ1-η1:η1 chelating mode coordinating to one zinc atom, respectively. The 1D chains are further joined together by bpp ligands to form a 2D layer structure (Figure 4c). It should be emphasized that the separation of Zn · · · Zn bridged by carboxylate group of bta3- in 4 is similar to those in 2 and 3, however, the separation of the Zn · · · Zn bridged by bpp in 4 is 11.70 Å, which is much shorter than those in 2 (13.49 Å) and 3 (13.34 Å) due to the great twist of C-C-C spacer in bpp. Two terminal pyridyl rings in bpp have a dihedral angle of 79.75°. Another point should be noticed is that the complex 4 is composed of the 2D network structure, while the complexes 1-3 exhibit 3D framework structure. The results further confirm that the structure and flexibility of the spacers in N-donor ligands have great impact on the structure of the complexes. Crystal Structure of [Cd2(bta)(bpy)2(H2O)]ClO4 · H2O 5. To investigate the influence of metal ion and counteranion on the structure of the complexes, reactions of H3bta with Cd(ClO4)2 · 6H2O and Cd(NO3)2 · 4H2O in the presence of bpy were carried out, respectively and 5 and 6 were obtained. Complex 5 crystallizes in monoclinic with space group P21/n. There are two different Cd(II) atoms in the asymmetric unit of 5 as shown in Figure 5a. The Cd1 lies in a distorted octahedral environment, in which the equatorial plane contains O3, O4 and O5A from two carboxylate groups of two bta3- ligands and O7 from a coordinated water molecule. The atoms N2 and N3A from two different bpy occupy the axial positions with N2-Cd1-N3A angle of 173.2(2)° (Table 2). Comparably, the Cd2 center with O5N2 donor set is coordinated by five carboxylate oxygen atoms from three different bta3- ligands and two nitrogen atoms from two different bpy ligands, displaying distorted pentagonal bipyramid geometry. On the other hand, each bta3- ligand coordinates with five Cd(II) atoms (Scheme S1e, Supporting Information). One carboxylate group adopts a µ1-η1:η1 chelating coordination mode to connect one Cd(II) atom while each of the other two carboxylate groups adopts a µ2-η2:η1 bridging coordination mode to link two Cd(II) atoms. As shown in Figure 5b, the carboxylate groups of the bta3- ligand connect the Cd1 and Cd2 atoms to form an infinite 1D chain with Cd1 · · · Cd2 and Cd2 · · · Cd1A distances of 4.423(1) and 4.478(1) Å, respectively. Such 1D chains are linked through the bta3- ligands to form a 2D stair-like structure (Figure 5c), since the planes formed by Cd(II) atoms and the carboxylate groups of the bta3- ligands is almost perpendicular to the center benzene ring plane of the bta3- ligands (Figure 5c). The 2D networks are further connected by bpy to form an unusual 3D cationic supramolecular architecture containing 1D channel (Figure 5d), in which the perchlorate anions and uncoordinated water molecules are located (Figure S2, Supporting Information). It is interesting that there are perchlorate anions in complex 5 obtained by reaction of H3bta with cadmium perchlorate and



Figure 5. (a) Crystal structure of complex 5 shown the coordination environment of Cd(II) with atom numbering scheme. The ellipsoids are drawn at the 30% probability level. Hydrogen atoms, perchlorate anions and uncoordinated water molecules are omitted for clarity. (b) Cd(II)-carboxylate 1D chain structure in complex 5. (c) 2D stair-like structure of complex 5. (d) 3D architecture of complex 5. Lattice water molecules and ClO4anions in the channels were omitted for clarity.

bpy, while in the cases of 1-4 and 6, obtained from zinc nitrate or cadmium nitrate, no nitrate anions were found in these complexes. The results imply that counteranion may have subtle influence on the structure of the complexes. Crystal Structure of [Cd3(bta)2(bpy)2] · 2H2O 6. Complex 6 was obtained by the reaction of H3bta and bpy with Cd(NO3)2 · 6H2O, instead of Cd(ClO4)2 · 6H2O used for preparation of 5. As shown in Figure 6a, the fundamental unit of 6 contains two hexacoordinated Cd(II) centers. The Cd1 center adopts a distorted octahedral geometry with O4N2 donor set, and is coordinated by four carboxylate oxygen atoms from four different bta3- ligands in the basal plane, and two nitrogen atoms from two bpy ligands occupy the apical positions; and the Cd2 center with O5N binding set is coordinated by five carboxylate oxygen atoms from three different bta3- ligands and one nitrogen atoms from the bpy ligand, displaying a distorted octahedral geometry. There are Cd2-Cd1-Cd2A trinuclear units with Cd1 · · · Cd2 distance of 3.84 Å linked by one carboxylate group and one oxygen atom from the other carboxylate group, which are further connected by bta3- ligands to generate a 2D network (Figure 6b and Figure S3, Supporting Information). The Zn1-Zn2-Zn1A trinuclear units and 2D network were also found in 1, however, the coordination geometry of Zn(II) in 1 and Cd(II) in 6 as well as the coordination modes of the bta3- ligands in 1 (Scheme S1a, Supporting Information) and 6 (Scheme S1f, Supporting Information) are different. The 2D networks in 6 are further pillared by bpy ligands to form a 3D supramolecular architecture

with 1D channel (Figure 6c). The 3D structures of 1 and 6 are also different, which can be seen from Figures 1d and 6c. There are uncoordinated water molecules filled in the vacancy of 3D framework in 6, but no water molecules are found in 1. The results show the effect of metal ions on the structure of the complexes due to their different coordination requirement. Crystal Structure of [Cd3(bta)2(H2O)2] 7. In contrast to the existence of ancillary ligand in each complex of 1 - 6, no phen was found in 7 although it was used as coligand in the preparation of 7. However, the phen molecules may play important role in the formation of 7, since the direct reaction of Cd(II) salt with H3bta resulted in formation of [Cd3(bta)2(H2O)7] · 5H2O.25 As illustrated in Figure 7a, there are also two different Cd(II) centers in the asymmetric structure of 7 with different coordination environments. The Cd1 atom with slightly distorted octahedral coordination geometry lies on an inversion center and is coordinated by two O atoms from water molecules and four O atoms from four different carboxylate groups, while the Cd2 is coordinated by six oxygen atoms from four different carboxylate groups. The Cd-O distances in 7 are in the range of 2.202(3)-2.609(4) Å which are similar to those observed in the reported complexes.26–28 On the other hand, each bta3- ligand adopts syn,anti,anti conformation and connects six Cd(II) atoms with three carboxylate groups adopting µ2-η2: η1- and µ2-η1:η1-bridging coordination modes (Scheme S1g and Figure S4, Supporting Information). It is interesting that the Cd1 and Cd2 atoms are linked together by the carboxylate groups to furnish a network with a distorted Kagome´ lattice


Liu et al.

Figure 6. (a) Crystal structure of complex 6 with the numbering scheme. The ellipsoids are drawn at the 30% probability level. Hydrogen atoms and uncoordinated water molecules are omitted for clarity. (b) Side view of the 2D network in complex 6. (c) 3D structure of complex 6. Green balls represent trinuclear units and yellow ones represent the centers of benzene rings of bta3- ligands.

(Figure 7b and c). All the Cd(II) atoms are located at the vertices of a Kagome´ lattice with distances between each two neighboring Cd(II) atoms of 4.1647(6), 4.5114(9) and 4.4293(6) Å, respectively. Such 2D Kagome´ networks are further connected by bta3- ligands to generate a 3D framework (Figure 7d). For bta3- ligand, one of the three carboxylate groups is coordinated to the Cd(II) atoms in one 2D Kagome´ network while the other two ones are coordinated to the Cd(II) atoms in the adjacent 2D Kagome´ network. Namely the Cd-carboxylate 2D inorganic layers are pillared by bta3- organic ligands into a 3D inorganic-organic alternate structure (Figure 7d) with the shortest interlayer Cd · · · Cd distance of 9.97 Å. Effect of N-Donor Ligands. In this study, diverse N-donor ligands with different coordination groups, conformations, and flexibility were used to investigate their influence on the structure of the Zn(II) and Cd(II) complexes. As for the rodlike bpy molecule, it is well-known as a bridging ligand as

reflected by the structure of complexes 1, 5, and 6, in which the metal-bta 2D layers are extended by the bpy ligands to result in the formation of 3D structures. In complex 2, another rigid ligand (dpe) was taken into the reaction, and a robust 3D structure was formed through the coordination of bta3- and dpe ligands with the Zn(II) atoms. In contrast to 1, uncoordinated water molecules in 2 occupy the vacancy between the 2D layers linked by dpe, while no such lattice water molecules were observed in 1 probably due to the short bpy pillar ligands. There are hydrogen bonds between the uncoordinated water molecule and carboxylate O atom since the distances of O1WsO3(-x, -y, -1-z) and O1WsO3(-1+x, y, z) are 2.972(7) and 3.030(11) Å. The hydrogen bonding data of 1-7 are summarized in Table S1 (Supporting Information). As for 3, a more flexible bpe is introduced as ancillary ligand, and the 2D layers are connected by bpe to form a 3D architecture, not only the presence of uncoordinated water molecules as that in 2, but also



Figure 7. (a) Coordination environment of Cd(II) with the ellipsoids drawn at the 30% probability level. The hydrogen atoms are omitted for clarity. (b) View of 2D network with Kagome´ lattice of 7. The benzene rings are omitted for clarify. (c) Schematic drawing of 2D network with Kagome´ lattice of 7. (d) Crystal packing diagram of 7.

the 2-fold interpenetration of the 3D frameworks. When another flexible bpp ligand was used, complex 4 with a 2D network structure, rather than the 3D framework in 1-3, was obtained, which may be attributed to the fact that the three methylene groups in bpp can rotate freely and the large degree of freedom prohibits the connection of 2D layers into a 3D structure. There are 2D networks formed by metal-bta coordination in complexes 1-6, which are further linked by ancillary ligands to give 3D frameworks (1-5) or 2D network (6), however, in 7, the coordination of bta3- with Cd(II) atoms forms 3D framework directly without ancillary ligand. Therefore, the N-donor ligands are found to play important role in determining the structure of the coordination architectures, with respect to their size, conformation, and degree of freedom.29 Photoluminescent Properties. Inorganic-organic hybrid coordination polymers, especially those with d10 metal centers, have been investigated for photoluminescent properties and for potential applications as fluorescence-emitting materials, such as light-emitting diodes (LEDs), owing to their higher thermal stability than the pure organic ligand and the ability to affect the emission wavelength of the organic material by metal coordination.30 Previous studies have shown that coordination polymers containing cadmium(II) and zinc(II) exhibit photoluminescent properties.12 The photoluminescent properties of 1-7 were investigated, and the results are provided in Figure 8. In

Figure 8. Solid-state fluorescence emissions recorded at room temperature for 1 (black), 2 (red), 3 (blue), 4 (dark cyan), 6 (magenta), and 7 (dark yellow).

the solid state, strong photoluminescence emission bands at 481 nm (λex ) 360 nm), 464 nm (λex ) 361 nm), 479 nm (λex ) 366 nm), 481 nm (λex ) 359 nm), 458 nm (λex ) 368 nm), and


451 nm (λex ) 354 nm) are observed for complexes 1-4, 6, and 7, respectively, whereas for complex 5, no clear luminescence was detected under the experimental conditions. For excitation wavelength between 280 and 480 nm, there is no obvious emission observed for free H3bta under the same experimental conditions, while free bpy, dpe, bpe, bpp ligands present weak photoluminescence emission. Therefore, the fluorescent emissions in the coordination polymers may be proposed to originate from the coordination of bta3- to the cadmium(II) and zinc(II) atoms.31 Conclusions By selecting Cd(II) or Zn(II) salts, bta3- and N-donor ligands as building blocks, seven new coordination polymers have been successfully isolated under hydrothermal conditions. The different structures of 1-4 are mainly caused by the different N-donor ancillary ligands, namely the different bridging ligand leads to the formation of the different frameworks. The different structures of Cd(II) and Zn(II) complexes are due to their different coordination geometry, counteranion plays an important role in the formation of cadmium(II) coordination polymers. Moreover, complexes 1-4, 6, and 7 display strong blue emissions at room temperature in the solid state. Acknowledgment. This work was financially supported by the National Science Fund for Distinguished Young Scholars (Grant no. 20425101), the National Natural Science Foundation of China (Grant no. 20731004 and 20721002), and the National Basic Research Program of China (Grant no. 2007CB925103). Supporting Information Available: X-ray crystallographic file in CIF format, coordination modes of bta3- (Scheme S1), TGA data (Figure S1) and structures of 5 (Figure S2), 6 (Figure S3), and 7 (Figure S4). This material is available free of charge via the Internet at http:// pubs.acs.org.

Liu et al.

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CG701137D

Effect of N-Donor Ancillary Ligands on Supramolecular Architectures

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