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DOI: 10.1021/cg100535q

Highly Connected Three-Dimensional Metal-Organic Frameworks Based on Polynuclear Secondary Building Units

2010, Vol. 10 3675–3684

Zhi Su, Shui-Sheng Chen, Jian Fan, Man-Sheng Chen, Yue Zhao, and Wei-Yin Sun* 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 April 22, 2010; Revised Manuscript Received June 13, 2010

ABSTRACT: A series of new highly connected MOFs [Cd(L)(PBEA)0.5] 3 H2O (1), [Cd2( μ3-OH)(L)(PBEA)] (2), [Cd3( μ3-OH)(L)2(PBEA)1.5] 3 H2O (3), and [Mn( μ2-H2O)(L)(PBEA)0.5] (4) have been synthesized by hydrothermal reactions of 3,5-di(imidazol1-yl)benzoic acid (HL) and 1,4-benzenediacetic acid (H2PBEA) with different metal salts, and these compounds were fully characterized by X-ray diffraction, IR, elemental analysis, TGA. The photoluminescence of 1-4 and magnetic property of 4 were investigated. Complex 1 is a binodal (3,8)-connected tfz-d net based on the binuclear [Cd2(COO)2] secondary building units (SBU1); while 2 is a binodal (3,10)-connected 3D net based on the tetranuclear motif [Cd4( μ3-OH)2(COO)6] (SBU2). Complex 3 is the first example of trinodal (3,8,10)-connected net based on SBU1 and SBU2, which can be considered as combination of the structural features presented in 1 and 2. Complex 4 is an unprecedented (3,8)-connected net based on the binuclear species [Mn2( μ2-H2O)(COO)2] (SBU3), which showed weak antiferromagnetic interactions between the metal ions. Complexes 1-3 were synthesized under the same experimental conditions except that different Cd(II) salts were used in the syntheses. Notably, although the counteranions of Cd(II) salts are absent from the resulting structures, yet they show subtle influence on the selfassembly process to provide different complexes. The approach of incorporating polynuclear metal cluster into highly connected frameworks and linking the SBUs by organic ligands provides opportunities for the design of new MOFs.

Introduction The design and construction of highly connected metalorganic frameworks (MOFs) has attracted much attention not only because of their intriguing structures and topologies but also for their potential application in many fields because of their enhanced stability and stable porosity.1 So far two strategies have been successfully developed to construct highly connected MOFs.2 One is to take advantage of relatively slim ligands and high coordination numbers of metal ions. It has been reported that the lanthanide ions can be coordinated by up to eight N-oxide donors without imposing severe steric constraints to the metal center.3 The other one is to use the polynuclear metal cluster as secondary building units (SBUs) to effectively reduce the steric hindrance between organic ligands, which provides a promising and feasible pathway toward the generation of highly connected MOFs. Generally, the specific topology associated with particular connectivity within a MOF can be analyzed and categorized with some natural prototype in metallic and binary inorganic solids. Up to now, the uninodal network topologies have been extensively studied, and the construction of binodal higher order framework also has been realized recently.4-6 However, the trinodal highly connected MOFs are exceedingly rare.7 Currently, considerable effort is devoted to enriching the structural library of highly connected MOFs, and the utilization of carboxylate group to construct such frameworks represents a mainstream method, although the synthetic conditions required to target a given cluster is not clear. It is well documented that the carboxylate group shows excellent coordination capability and flexible coordination patterns.8 In particular,

it can prompt core aggregation via bridging metal ions and fixing their position into metal cluster. Furthermore frameworks constructed from metal-carboxylate interactions may exhibit high stability and permanent porosity upon desolvation. Taking these into account, in this work we chose 1,4-benzenediacetic acid (H2PBEA) and 3,5-di(1H-imidazol-1-yl)benzoic acid (HL) as linkers based on the following considerations: (i) H2PBEA ligand may show a variety of coordination modes and conformations because of the increased flexibility of two carboxylate groups as compared to the rigid terephthalic acid, thus make it easier to form polynuclear cluster in situ than to form single metal-ion precursor. (ii) Our systematic research shows that the rigid imidazole-containing tripodal ligand can act as a multidentate ligand to link the metal cluster into an extended network, moreover it is responsible for the stability of the framework.9 Herein, we report the synthesis and characterization of four highly connected MOFs: [Cd(L)(PBEA)0.5] 3 H 2O (1), [Cd2 ( μ3 -OH)(L)(PBEA)] (2), [Cd3( μ 3-OH)(L)2(PBEA)1.5] 3 H2O (3), and [Mn( μ2-H2O)(L)(PBEA)0.5] (4). It is interesting that assembly reactions of three Cd(II) salts with the mixture of HL and H2PBEA provide different complexes 1-3; while reactions of varied Mn(II) salts with the mixed linkers lead to the same product (complex 4). Experimental Section

*To whom correspondence should be addressed. Telephone: þ86-2583593485. Fax: þ86-25-83314502. E-mail: [email protected].

All commercially available chemicals are of reagent grade and were used as received without further purification. The ligand HL was prepared according to the procedures reported previously.10 Elemental analyses of C, H, and N were taken on a Perkin-Elmer 240C elemental analyzer at the analysis center of Nanjing University. Infrared spectra (IR) were recorded on a Bruker Vector22 FT-IR spectrophotometer by using KBr pellets. Thermogravimetric analyses (TGA) were performed on a simultaneous SDT 2960 thermal analyzer under nitrogen with a heating rate of 10 °C min-1. The luminescence spectra for the

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Table 1. Crystallographic Data for Complexes 1-4 empirical formula formula weight temperature/K crystal system space group a/A˚ b/A˚ c/A˚ R/deg β/deg γ/deg V/A˚3 Z Dc (g cm-3) F(000) θrange/deg reflns collected independent reflns goodness-of-fit R1a (I > 2σ (I)) R2b (I > 2σ (I)) R1 (all data) R2 (all data)

2

3

4

C23H18Cd2N4O7 687.21 293(2) triclinic P1 10.7012(7) 11.0545(13) 11.1571(7) 104.4250(10) 116.124(2) 97.3723(10) 1103.82(16) 2 2.068 672 1.98 - 25.25 5702 3941 0.926 0.0264 0.0547 0.0364 0.0578

C41H33Cd3N8O12 1166.93 293(2) triclinic P1 10.936(6) 11.496(7) 17.654(10) 84.706(7) 74.308(2) 69.543(7) 2002(2) 2 1.931 1162 2.06 - 25.25 10319 7146 1.057 0.0318 0.0862 0.0358 0.0953

C36H28Mn2N8O9 826.54 293(2) monoclinic C2/c 12.0613(14) 17.8712(16) 16.3160(12) 90 91.555(2) 90 3515.6(6) 4 1.562 1688 2.04 - 25.24 8787 3167 0.764 0.0367 0.1072 0.0400 0.1109

)

R1 =Σ Fo| - |Fc /Σ|Fo|. b R2 = |Σw(|Fo|2 - |Fc|2)|/Σ|w(Fo)2|1/2, where w = 1/[σ2(Fo2) þ(aP)2þbP]. P = (Fo2 þ 2Fc2)/3. )

a

1 C18H15CdN4O5 479.74 293(2) triclinic P1 9.841(2) 10.5070(12) 10.7063(17) 60.675(1) 65.591(2) 77.719(2) 878.8(2) 2 1.805 474 2.22 - 25.25 4518 3136 1.18 0.0324 0.0933 0.0373 0.1122

powdered solid samples were measured at room temperature on an Aminco Bowman Series2 spectrofluorometer with a xenon arc lamp as the light source. In the measurements of emission and excitation spectra, the pass width is 5 nm. All the measurements were carried out under the same experimental conditions. The magnetic measurements in the temperature range of 1.8 to 300 K were carried out on a Quantum Design MPMS7 SQUID magnetometer in a field of 2000 Oe. Diamagnetic corrections were made with Pascal’s constants for all samples. Preparation of [Cd(L)(PBEA)0.5] 3 H2O (1). A mixture of Cd(NO3)2 3 6H2O (29.7 mg, 0.1 mmol), HL (12.7 mg, 0.05 mmol), H2PBEA (8.7 mg, 0.05 mmol), NaOH (6.0 mg, 0.15 mmol), and H2O (10 mL) was sealed in a 16 mL Teflon-lined stainless steel container and heated at 180 °C for 3 d. Complex 1 was isolated from the mixture in colorless block crystalline form by filtration and washed by water and ethanol several times with a yield of 14.87 mg (0.031 mmol, 62%). Anal. Calcd for C18H15CdN4O5 (%): C, 45.06; H, 3.15; N, 11.68. Found: C, 45.10; H, 3.11; N, 11.64. IR (KBr, cm-1): 3446(br,s), 1587(s) 1565(s), 1508(s), 1400(s), 1365(s), 1259(w), 1242(m), 1144(m), 1175(w), 1066(m), 1015(w), 934(m), 878(w), 821(w), 759(m), 721(m), 673(w), 644(m), 587(w). Preparation of [Cd2( μ3-OH)(L)(PBEA)] (2). Complex 2 was synthesized by the same procedure as for the preparation of 1, except that CdCl2 3 2.5H2O (22.8 mg, 0.1 mmol) was used instead of Cd(NO3)2 3 6H2O as the starting material. Colorless block crystals of 2 were isolated by filtration and washed by water and ethanol several times with a yield of 19.24 mg (0.028 mmol, 56%). Anal. Calcd for C23H18Cd2N4O7 (%): C, 40.20; H, 2.64; N, 8.15. Found: C, 40.17; H, 2.66; N, 8.11. IR (KBr, cm-1): 3443(br), 1586(s), 1571(s), 1505(s), 1400(s), 1384(s), 1331(w), 1241(m), 1144(w), 1114(w), 1066(m), 1014(w), 933(m), 823(w), 782(w), 756(m), 721(m), 674(w), 644(m), 587(w). Preparation of [Cd3( μ3-OH)(L)2(PBEA)1.5] 3 H2O (3). Complex 3 was also synthesized by the same procedure as for the preparation of 1, except that CdSO4 3 8/3H2O (25.6 mg, 0.1 mmol) was used instead of Cd(NO3)2 3 6H2O as the starting material. Colorless block crystals of 3 were obtained by filtration and washed by water and ethanol several times with a yield of 21.00 mg (0.018 mmol, 54%). Anal. Calcd for C41H33Cd3N8O12 (%): C, 42.20; H, 2.85; N, 9.60. Found: C, 41.55; H, 2.91; N, 9.42. IR (KBr, cm-1): 3446(br), 1584(s), 1568(s), 1506(s), 1396(s), 1364(s), 1330(w), 1267(w), 1240(m), 1114(w), 1067(m), 1059(m), 1016(m), 932(m), 826(w), 786(m), 758(w), 736(m), 703(w), 647(m), 587(w). Preparation of [Mn( μ2-H2O)(L)(PBEA)0.5] (4). Complex 4 was synthesized by the same procedure as that used for preparation of 1, except that MnCl2 3 4H2O (19.7 mg, 0.1 mmol), Mn(NO3)2 3 4H2O (25.1 mg, 0.1 mmol), or MnSO4 3 H2O (16.9 mg, 0.1 mmol) was used

instead of Cd(NO3)2 3 6H2O as the starting material. Pink block crystals of 4 were isolated from the mixture by filtration and washed by water and ethanol several times with a yield of 27.69 mg (0.034 mmol, 67%) for MnCl2 3 4H2O, 20.66 mg (0.025 mmol, 50%) for Mn(NO3)2 3 4H2O and 21.90 mg (0.027 mmol, 53%) for MnSO4 3 H2O, respectively. Anal. Calcd for C36H28Mn2N8O9 (%): C, 52.31; H, 3.41; N, 13.56. Found: C, 52.34; H, 3.40; N, 13.52. IR (KBr, cm-1): 3431(br), 1639(s), 1590(s), 1501(s), 1407(s), 1384(s), 1372(s), 1302(m), 1267(m), 1231(m), 1107(w), 1069(s), 1014(w), 927(m), 830(w), 813(w), 773(w), 705(m), 655(w), 601(w). Single-Crystal X-ray Crystallography. The crystallographic data collections for 1-4 were carried out on a Bruker Smart Apex CCD area-detector diffractometer with graphite-monochromated Mo KR radiation (λ=0.71073 A˚) at 20(2) °C using the ω-scan technique. The diffraction data were 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 non-hydrogen atoms were refined anisotropically on F2 by the full-matrix least-squares technique using the SHELXL-97 crystallographic software package.13 All the hydrogen atoms of ligands L- and PBEA2- in complexes 1-4 were generated geometrically. The hydrogen atoms of hydroxyl group in 2 and 3, and the ones of water molecule in 4 were located directly. Atoms C9 and C10 in 2 disordered into two positions with site occupancy factors of 0.65(3) and 0.35(3), respectively and free water molecule (O12) in 3 also have two positions with site occupancy factors of 0.70(2) and 0.30(2), respectively. All calculations were performed on a personal computer with the SHELXL-97 crystallographic software package. Details of the crystal parameters, data collection and refinements for 1-4 are summarized in Table 1. Selected bond lengths and angles for 1-4 are listed in Table 2. Further details are provided in the Supporting Information.

Results and Discussion Synthesis and Thermal Stabilities of the Complexes. Reactions of Cd(NO3)2 3 6H2O, CdCl2 3 2.5H2O, and CdSO4 3 8/3H2O with mixed ligands of HL and H2PBEA in the presence of NaOH afforded complexes [Cd(L)(PBEA)0.5] 3 H2O (1), [Cd2( μ3-OH)(L)(PBEA)] (2), and [Cd3( μ3-OH)(L)2(PBEA)1.5] 3 H2O (3), respectively. On the contrary, reactions of different Mn(II) salts (see Experimental Section) with HL, H2PBEA, and NaOH under the same conditions as for the preparation

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of 1-3 generated the same product [Mn( μ2-H2O)(L)(PBEA)0.5] (4), which may be ascribed to the different nature (e.g., ion radius,

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coordination number and geometry) of metal ions.14,15 The reactions with the same reactants were also carried out at 140 and

Table 2. Selected Bond Lengths (A˚) and Bond Angles (deg) for Complexes 1-4 1a Cd1-O3 Cd1-N3 Cd1-N1#1 O3-Cd1-N3 O3-Cd1-N1#1 O1#2-Cd1-O3 O3-Cd1-O4#3 N1#1-Cd1-N3

2.266(4) 2.270(4) 2.251(4) 93.26(13) 130.64(14) 96.64(12) 103.57(11) 135.87(14)

Cd1-O1#2 Cd1-O4#3 O1#2-Cd1-N3 O4#3-Cd1-N3 O1#2-Cd1-N1#1 O4#3-Cd1-N1#1 O1#2-Cd1-O4#3

2.267(3) 2.490(3) 83.65(12) 79.99(11) 93.83(12) 84.67(12) 154.57(11)

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

2.239(3) 2.256(3) 2.352(3) 2.360(2) 2.209(3) 2.242(3) 2.252(2) 163.11(11) 79.66(10) 95.08(10) 96.15(9) 83.30(10) 160.02(10) 79.88(10) 83.27(11) 75.56(9) 84.48(10) 88.62(9) 113.02(10) 94.13(10) 93.63(10) 131.30(9) 115.10(11) 89.99(10) 80.50(9)

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

2.448(3) 2.516(3) 2.554(3) 2.259(3) 2.353(2) 2.563(3)

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

108.12(11) 113.63(9) 85.60(9) 163.90(9) 112.42(9) 80.94(10) 73.78(9) 125.23(9) 143.91(9) 51.43(8) 86.36(10) 174.14(10) 95.33(10) 77.92(9) 164.70(11) 96.25(9) 53.40(9) 84.99(9)

Cd(1)-O(9) Cd(1)-O(7)#3 Cd(1)-O(10) Cd(2)-O(4)#2 Cd(2)-O(8)#6 Cd(2)-O(7)#6 Cd(3)-N(1)#7 Cd(3)-O(6)#1 Cd(3)-O(5) O(3)#2-Cd(1)-O(7)#3 O(9)-Cd(1)-O(7)#3 O(11)-Cd(1)-O(10) N(5)-Cd(1)-O(10) O(3)#2-Cd(1)-O(10) O(9)-Cd(1)-O(10) O(7)#3-Cd(1)-O(10) N(3)#4-Cd(2)-O(8)#6 O(11)#5-Cd(2)-O(8)#6 N(3)#4-Cd(2)-O(10) O(4)#2-Cd(2)-O(10) Cd(2)-O(10)-O(7)#6 O(4)#2--d(2)-O(8)#6 O(11)-Cd(2)-O(7)#6 N(3)#4-Cd(2)-O(7)#6 O(11)#5-Cd(2)-O(7)#6 O(4)#2-Cd(2)-O(7)#6 O(8)#6-Cd(2)-O(7)#6 O(1)-Cd(3)-N(1)#7 O(5)-Cd(3)-O(6)#1 N(7)-Cd(3)-O(6)#1 O(1)-Cd(3)-O(6)#1 N(1)#7-Cd(3)-O(6)#1

2.288(3) 2.341(3) 2.509(3) 2.386(3) 2.439(3) 2.607(3) 2.271(3) 2.489(3) 2.238(3) 174.43(10) 98.71(11) 77.18(10) 165.28(11) 100.23(11) 53.71(10) 83.74(10) 107.14(12) 114.94(9) 83.61(12) 83.01(11) 141.83(10) 88.25(10) 113.97(9) 79.34(11) 73.18(9) 128.85(10) 51.65(9) 86.74(11) 98.84(10) 85.82(11) 160.60(10) 79.40(11)

3c Cd(1)-O(11) Cd(1)-N(5) Cd(1)-O(3)#2 Cd(2)-O(11) Cd(2)-N(3)#4 Cd(2)-O(11)#5 Cd(2)-O(10) Cd(3)-N(7) Cd(3)-O(1) O(11)-Cd(1)-N(5) O(11)-Cd(1)-O(3)#2 N(5)-Cd(1)-O(3)#2 O(11)-Cd(1)-O(9) N(5)-Cd(1)-O(9) O(3)#2-Cd(1)-O(9) O(11)-Cd(1)-O(7)#3 N(5)-Cd(1)-O(7)#3 O(11)-Cd(2)-N(3)#4 O(10)-Cd(2)-O11 O(11)#5-Cd(2)-O(10) O(10)-Cd(2)-O(8)#6 O(11)-Cd(2)-O(11)#5 N(3)#4-Cd(2)-O(11)#5 O(11)-Cd(2)-O(4)#2 N(3)#4-Cd(2)-O(4)#2 O(11)#5-Cd(2)-O(4)#2 O(11)-Cd(2)-O(8)#6 O(5)-Cd(3)-N(7) O(5)-Cd(3)-O(1) N(7)-Cd(3)-O(1) O(5)-Cd(3)-N(1)#7 N(7)-Cd(3)-N(1)#7

2.223(3) 2.240(3) 2.244(3) 2.223(3) 2.259(3) 2.375(3) 2.495(3) 2.242(4) 2.271(3) 113.01(11) 95.69(11) 89.57(11) 130.30(10) 116.65(12) 86.82(12) 81.31(10) 87.31(11) 160.84(12) 77.34(12) 73.58(11) 165.62(11) 80.24(10) 91.35(11) 95.15(9) 85.67(11) 156.36(10) 92.01(10) 129.86(12) 96.16(11) 93.96(11) 96.61(12) 132.96(12)

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Su et al. Table 2. Continued 4d

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

2.1055(15) 2.1328(15) 2.1993(14) 174.54(6) 88.73(6) 92.83(6) 94.10(7) 91.21(7) 86.70(6) 84.83(5) 88.21(6)

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

2.2671(17) 2.2605(13) 2.2585(19) 89.80(5) 96.05(5) 177.02(6) 90.99(6) 87.85(6) 175.68(6) 89.02(7)

a Symmetry transformations used to generate equivalent atoms for 1: #1 -1 þ x, -1 þ y, 1 þ z; #2 x, -1 þ y, 1 þ z; #3 1 - x, -y, 1 - z. b Symmetry transformations used to generate equivalent atoms for 2: #1 -x þ 2, -y þ 1, -z; #2 x þ 1, y, z; #3 x, y þ 1, z. c Symmetry transformations used to generate equivalent atoms for 3: #1 -x, -y, -z þ 1; #2 x þ 1, y, z; #3 x, y þ 1, z; #4 x þ 1, y þ 1, z - 1; #5 -x þ 2, -y þ 1, -z; #6 -x þ 2, -y, -z; #7 x - 1, y, z. d Symmetry transformations used to generate equivalent atoms for 4: #1 x þ 1/2, y þ 1/2, z; #2 -x, y, -z þ 1/2; #3 -x þ 1/2, -y þ 3/2, -z.

Figure 1. (a) Coordination environment of Cd(II) in 1 with ellipsoids drawn at the 30% probability level; hydrogen atoms and free water molecule are omitted for clarity. Symmetry codes: A, 1 - x, -1 - y, 1 - z; B, -1 þ x, -1 þ y, 1 þ z; C, x, -1 þ y, 1 þ z; D, 1 - x, -y, 1 - z. (b) The PBEA-SBU1 1D chain in 1. (c) The L-SBU1 2D network in 1. (d) The 3D framework of 1. (e) The (3, 8)-connected tfz-d net of 1 (violet nodes, SBU1; green, L-).

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160 °C, respectively, and the same products were obtained. The pure phase of the complexes were proved by the powder X-ray diffraction (PXRD), where the as-synthesized ones of 1-4 are consistent with the simulated ones (Figure S1, Supporting Information). It is well established that the counterions play important role during the self-assembly process when they are incorporated in the resulting framework, and show negligible role when they are absent from the final structure.6,9,16 It is notable that in the case of 1-3, the counterions show subtle but significant influence on assembly reactions to generate different structures although the counterions are not involved in the structures. In the preparation of 1-4 the carboxylate groups of HL and H2PBEA were completely deprotonated by NaOH, which was confirmed by crystallographic analysis (vide infra) as well as the IR spectral data. The IR bands in the range of 17601680 cm-1 corresponding to -COOH functional group were not observed in the IR spectra of 1-4 (see Experimental Section). To investigate the mobility of the solvent molecules within the MOFs, thermogravimetric analyses (TGA) were carried out for 1-4, and the results are shown in Figure S2, Supporting Information. Complex 1 shows a weight loss of 4.29% in the temperature range of 180-230 °C, which is attributed to the release of the uncoordinated water molecules (calcd 3.76%), and the decomposition of the residue occurs at 325 °C. No obvious weight loss was found for 2 before the decomposition of the framework occurred at about 370 °C. For 3, there is a weight loss of 2.06% in the temperature range of 90-180 °C, corresponding to the departure of the free water molecules (calcd 1.55%), and further weight loss was observed at about 360 °C. No obvious weight loss for 4 was observed before the framework decomposition occurs at 310 °C, indicating the μ2-H2O molecules are strongly binding to the metal centers. It is noteworthy that the free water molecules in 1 and 3 were lost at different temperatures, which is consistent with the results of crystal structural analysis. The disordered free water molecule in 3 implies the high thermal motion leading to the loss at low temperature, while the nondisordered one in 1 is linked to the framework through the O-H 3 3 3 O hydrogen bond with O5 3 3 3 O2 distance of 2.73 A˚. Crystal Structure of [Cd(L)(PBEA)0.5] 3 H2O (1). The asymmetric unit of compound 1 contains one Cd(II), one L-, half PBEA2- ligand, and one lattice water molecule. Each Cd(II) atom is five-coordinated by two imidazole nitrogen atoms (N1B, N3) and one oxygen atom (O1C) from three distinct Lligand and other two oxygen atoms (O3, O4D) from two different PBEA2- ligands to complete a distorted trigonal bipyramid coordination geometry (Figure 1a). The equatorial plane is defined by N1B, N3, and O3, and the axial positions are occupied by O1C and O4D with a O1C-Cd1-O4D angle of 154.57(11)° (Table 2). A distance of 2.69 A˚ (Cd1-O4), which is longer than the ones observed in the previously reported Cd(II) complexes,14 indicates that there is weak interaction between Cd1 and O4. On the other hand, each PBEA2- ligand links four Cd(II) atoms with each carboxylate group in a μ2-η1:η1-bismonodentate mode (Scheme 1a). In 1 two neighboring Cd(II) ions are connected together by two μ2-η1:η1-bis-monodentate carboxylate groups to form a binuclear motif (SBU1) with a Cd 3 3 3 Cd separation of 4.15 A˚ (Scheme 2a). As shown in Figure 1b, the SBU1s are joined by PBEA2- ligands to form an infinite one-dimensional (1D) chain along the b direction. Meanwhile, each L- ligand links three SBU1s to form a twodimensional (2D) layer (Figure 1c) with the carboxylate group

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Scheme 1. Different Coordination Modes of PBEA2- and L- in Complexes 1-4a

a For each carboxylate group: μ2-η1:η1-bis-monodentate mode (a and f); μ2-η2:η1-brigding mode (b); μ2-η1:η1-bis-monodentate and μ2-η2:η1-brigding modes (c); μ1-η1:η0-monodentate mode (d and e).

Scheme 2. Schematic View of the SBU1 (a), SBU2 (b), and SBU3 (c) Appeared in 1-4

of L- in a μ1-η1:η0-monodentate fashion (Scheme 1d). This 2D layer is a hexagonal kgd (Kagome dual) net if the SBU1 and Lligand are considered as six- and three-connectors, respectively (Figure S3, Supporting Information).17 The adjacent 2D layers were further pillared by the PBEA2- ligands to generate the (3,8)afli) connected tfz-d net (Figure 1d and e).18 The Point (Schl€ symbols for compound 1 is (43)2(46 3 618 3 84). Crystal Structure of [Cd2( μ3-OH)(L)(PBEA)] (2). The asymmetric unit of compound 2 contains two Cd(II) ions, one L-, two half PBEA2- ligands (from two crystallographically

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Figure 2. (a) Coordination environment of Cd(II) in 2 with ellipsoids drawn at the 30% probability level; hydrogen atoms are omitted for clarity. Symmetry codes: A 3 - x, 1 - y, 1 - z; B 2 - x, -y, -1 - z; C x þ 1, y, z; D x, y þ 1, z; E -x þ 2, -y þ 1, -z. (b) The PBEA-SBU2 (4,4) 2D layer in 2. (c) The L-SBU2 2D network in 2. (d) The 3D framework of 2. (e) The (3,10)-connected net of 2 (pink nodes, SBU2; green, L-).

independent ligands), and one μ3-hydroxide anion. As shown in Figure 2a, the Cd1 center with distorted pentagonal bipyramid coordination geometry is seven-coordinated by three carboxylate oxygen atoms (O3, O5, O6) from two PBEA2- ligands, one imidazole nitrogen atom (N1C) and one carboxylate oxygen atom (O1) from L- ligands, and two μ3-hydroxyl oxygen atoms (O7, O7E). The Cd1-O bond lengths are in the range of 2.239(3)-2.554(3) A˚ with an average value of 2.41 A˚ (Table 2). The Cd2 with distorted octahedral geometry is six-coordinated by three carboxylate oxygen atoms (O3, O4, O5E) from two PBEA2- ligands, one imidazole nitrogen atom (N3D) and one carboxylate oxygen atom (O2) from L- ligands, and one μ3-hydroxyl oxygen atom (O7E). The Cd2-O bond lengths are in the range of 2.209(3)-2.563(3) A˚ with an average value of 2.33 A˚ (Table 2). In 2, one hydroxide anion (O7E) links three Cd(II) (Cd1, Cd1#1 [symmetry code #1 2 - x, 1 - y, -z] and Cd2) together to form a Cd3( μ3-OH) fragment, and two symmetric related Cd3( μ3-OH) fragments share a Cd1 3 3 3 Cd1#1 edge, yielding a tetranuclear Cd4( μ3-OH)2 cluster (SBU2) located across an inversion center (Scheme 2b). Within this cluster the Cd1 3 3 3 Cd1#1 distance is 3.53 A˚, and the Cd2 3 3 3 Cd2#1 one is 6.14 A˚. In 2, each carboxylate group of PBEA2- adopts a μ3-η1:η2-brigding mode to knit the SBU2s into a puckered (4,4) net (Scheme 1b, Figures 2b and S4). The carboxylate group of L- ligand adopts a μ2-η1:η1-bridging mode coordinating to

two Cd(II) atoms, and each imidazole group links one Cd(II) atom (Scheme 1f). Accordingly, the L- ligand in 2 acting as a three connector bridges the SBU2s to form a 2D (3,6)-connected hexagonal kgd net (Figure 2c), which is similar to that observed in complex 1. The interconnection of tetranuclear cluster by L- and PBEA2- leads to a binodal (3,10)-connected 3D net (Figures 2d and 2e). The Point (Schl€ afli) symbols for compound 2 is (43)2(418 3 624 3 83). Crystal Structure of [Cd3( μ3-OH)(L)2(PBEA)1.5] 3 H2O (3). The asymmetric unit of compound 3 contains three crystallographically different Cd(II) atoms, two L- units, one and half PBEA2- ligands, one μ3-hydroxide anion, and one lattice water molecule. As shown in Figure 3a, the Cd1 center with distorted octahedral geometry is six-coordinated by three oxygen atoms (O7C, O9, O10) from two distinct PBEA2ligands, one imidazole nitrogen atom (N5), one oxygen atom (O3B) from L- ligands, and one μ3-hydroxyl oxygen atom (O11). The Cd1-O bond lengths are in the range of 2.223(3)2.509(3) A˚ with an average value of 2.31 A˚ (Table 2). The Cd2 center with distorted pentagonal bipyramid coordination geometry is seven-coordinated by three oxygen atoms (O7E, O8E, O10) from two different PBEA2- ligands, one imidazole nitrogen atom (N3D) and one oxygen atom (O4B) from two distinct L- ligands, and two μ3-hydroxyl oxygen atoms (O11, O11F). The Cd2-O bond lengths are in the

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Figure 3. (a) Coordination environment of Cd(II) in 3 with ellipsoids drawn at the 30% probability level; hydrogen atoms and free water molecule are omitted for clarity. Symmetry codes: A 2 - x, 2 - y, -z; B x þ 1, y, z; C x, y þ 1, z; D x þ 1, y þ 1, z - 1; E -x þ 2, -y, -z; F -x þ 2, -y þ 1, -z; G x - 1, y, z; H -x, -y, -z þ 1. (b) The PBEA-SBU1-SBU2 (4, 4) 2D layer in 3. (c) The L-SBU1-SBU2 2D network in 3. (d) The 3D framework of 3. (e) The (3,8,10)-connected net of 3 (violet nodes, SBU1; pink, SBU2; green, L-).

range of 2.223(3)-2.607(3) A˚ with an average value of 2.40 A˚ (Table 2). In 3 four Cd(II) atoms (Cd1, Cd1#2, Cd2, and Cd2#2 [symmetry code #2 2 - x, 1 - y, -z]) are bridged together with the same pattern as observed in complex 2 to form a tetranuclear Cd4( μ3-OH)2 cluster (SBU2) (Scheme 2b). The Cd3 center with distorted square pyramidal coordination geometry is five-coordinated by two imidazole nitrogen atoms (N1G, N7) and one oxygen atom (O1) from three different L- ligands, and two oxygen atom (O5, O6H) from two different PBEA2- ligands. The average Cd3-O and Cd3-N bond lengths are 2.33 and 2.26 A˚, respectively. The Cd3 3 3 3 O6 distance of 2.79 A˚ shows weak interaction between the two atoms. Two Cd3 centers are linked together by two carboxylate groups to yield a binuclear motif (SBU1) with the Cd 3 3 3 Cd separation of 4.33 A˚ (Scheme 2a). In complex 3, there are two coordination patterns for PBEA2- ligands with the two carboxylate groups either both in a μ2-η1:η2-brigding mode (Scheme 1b) or one in a μ2-η1:η2brigding and the other one in a μ2-η1:η1-bridging modes (Scheme 1c). As illustrated in Figure 3b, the interconnection of SBU1 and SBU2 by PBEA2- ligands affords a (4, 4) net, where the SBU1 linked by two PBEA2- ligands is located at the mid of two SBU2 units (Figures 3b and S5). The Lligands in 3 adopt two coordination modes with carboxylate group either in a μ1-η1:η0-monodentate fashion as observed in 1 (Scheme 1e) or in a μ2-η1:η1-bridging mode as observed in 2 (Scheme 1f). The interconnection of SBU1 and SBU2 by

L- ligands generates a 2D (3,6)-connected hexagonal kgd net layer (Figure 3c), which is further pillared by PBEA2- ligands to form a 3D framework (Figure 3d). Complex 3 represents an unprecedented trinodal (3,8,10)-connected net with Point (Schl€ afli) symbols (43)4(410 3 615 3 83)(412 3 626 3 87) (Figure 3e). Crystal Structure of [Mn( μ2-H2O)(L)(PBEA)0.5] (4). The asymmetric unit of compound 4 contains one Mn(II), one L-, half PBEA2- ligand, and one μ2-H2O molecule. Each Mn1 atom with slight distorted octahedral coordination geometry is six coordinated by two oxygen atoms (O1D, O2) and two nitrogen atoms (N1B, N3C) from four distinct Lligands, one oxygen atom (O4) from one PBEA2- ligand and one μ2-H2O molecule (O5) (Figure 4a). The Mn1-O distances are in the range of 2.1055(15)-2.2605(13) A˚, and the Mn1-N3c and Mn1-N1B distances are 2.2585(19) and 2.2671(17) A˚, respectively (Table 2). On the other hand, the carboxylate group of L- adopts a μ2-η1:η1-brigding mode (Scheme 1f), and each carboxylate group of PBEA2acts as a monodentate (Scheme 1d). In 4, two neighboring Mn(II) atoms are connected together by one μ2-H2O molecule and two carboxylate groups from two different L- ligands to form the SBU3 with Mn 3 3 3 Mn separation of 3.68 A˚ (Scheme 2c). The PBEA2- ligands coordinate to the SBU3s to form a 1D chain (Figure 4b), while each L- ligand links three SBU3 units to afford a 3D (3,6)-connected anatase (ant) net with Point (Schl€ afli) symbols (42 3 6)2(44 3 62 3 88 3 10) (Figures 4c and S6).19 As shown in

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Figure 4. (a) Coordination environment of Mn(II) in 4 with ellipsoids drawn at the 30% probability level; hydrogen atoms are omitted for clarity. Symmetry codes: A 1 - x, y, 1/2 - z; B x þ 1/2, y þ 1/2, z; C -x þ 1/2, -y þ 3/2, -z; D -x, y, -z þ 1/2. (b) The PBEA-SBU3 1D chain in 4. (c) The 3D framework of L-SBU3 in 4. (d) The 3D framework of 4. (e) The unprecedented (3,8)-connected net of 4 (violet nodes, SBU3; green, L- ligands).

Figure 4d, PBEA2- ligands are located in the open channels of L-SBU3 3D framework via coordination bonds. Thus, complex 4 is an unprecedented binodal (3,8)-connected framework with Point (Schl€afli) symbols (42 3 5)2(44 3 56 3 610 3 75 3 82 3 9) as schematically shown in Figure 4e. Structural Comparison. Complexes 1-3 adopt pillaredlayer structures. In 1-3, the 2D layers with kgd topology are constructed by L- ligands and metal clusters, and PBEA2- ligands acting as pillars link the 2D layers to form the 3D frameworks. In 4, the metal clusters are connected by L- ligands to generate a 3D anatase (ant) net, and PBEA2ligands are fixed in the voids of 3D framework via coordination bonds. In 1, the binuclear SBU1 is formed serving as an eight-connected node, and in 2, the tetranuclear SBU2 acts as ten-connected node. Interestingly both SBU1 and SBU2 are observed in 3, which can be considered as a combination of the structural features presented in complexes 1 and 2.

In 1, 3, and 4, the eight-connected nodes (SBU1 or SBU3) are linked by PBEA2- ligands to form the 1D chain, while in 2 and 3, the ten-connected nodes (SBU2) are bridged by PBEA2- ligands to generate the 2D (4, 4) net. In addition, four PBEA2- ligands and four SBU2 units form a macrocycle in 2, which is enlarged in 3 by the intercalation of two SBU1 units. Magnetic Properties of 4. The temperature dependence of magnetic susceptibility of 4 in the form of χMT and χM versus T is displayed in Figure 5. At room temperature, the value of χMT is 8.43 emu K mol-1, which is slightly lower than the value of 8.75 emu K mol-1 expected for two uncoupled Mn(II) ions (g = 2, S1 = S2 = 5/2). Upon cooling, the χMT values decrease slowly and then more rapidly below 75 K to reach the value of 0.32 emu K mol-1 at 1.8 K, indicating the antiferromagnetic coupling between the Mn(II) ions. As shown in the structure description, 4 is a 3D framework

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Figure 5. Temperature dependences of magnetic susceptibility of χM and χMT for 4. The solid lines represent the fitted curves.

based on SBU3, so it could be considered that the main magnetic interactions between the metal centers occur between the carboxylate and μ2-H2O molecule bridged Mn(II) ions whereas the superexchange interactions between the Mn(II) ions linked through the PBEA2- and L- ligands can be ignored for their long distances of 8.62 - 11.58 A˚. The magnetic susceptibility data were fitted assuming that the carboxylate and μ2-H2O bridged Mn(II) ions form an isolated spin dimer system. And the mean-field corrections zj0 were taken into account, the magnetic susceptibility in the whole temperature range was fitted according to the eqs 1 and 2, which are ^ = -2JS1S214 based on the spin Hamiltonian H χ ¼ 

2Ng2 β2 kT 55e30J=kT þ 30e20J=kT þ 14e12J=kT þ 5e6J=kT þ e2J=kT 11e30J=kT þ 9e20J=kT þ 7e12J=kT þ 5e6J=kT þ 3e2J=kT þ 1 ð1Þ χM ¼

χ 1 - ð2zj0 =Ng2 β2 Þχ

ð2Þ

where N is Avogadro’s number, μB is the Bohr Magneton, kB is Boltzmann’s constant, and g is the Lande g value. The best fit in the range of 1.8-300 K gave values of g = 2.003, J = -1 -1 , and the agreement factor -1.244 P cm , zj’ = -0.067 cm 2 P R= [(χMT)obsd - (χMT)calcd] / (χMT)2 =3.6  10-4, which is comparable with those in the carboxylate bridged Mn(II) compounds reported previously.20 The negative value of J confirms that there exist antiferromagnetic interactions within SBU3 in 4. Luminescent Properties of 1-4. Previously studies have shown that inorganic-organic hybrid coordination polymers, especially with d10 metal centers, exhibit photoluminescent properties and have potential application as fluorescenceemitting materials.21 The photoluminescence properties of 1-4 together with the HL and H2PBEA ligands were investigated in the solid state at room temperature and all measurements of emission spectra were excited at a wavelength of 397 nm. As shown in Figure 6, intense photoluminescence emission bands at 466, 467, 469, and 446 nm were observed for complexes 1-3 and free H2PBEA ligand, respectively, whereas no clear luminescence was detected for 4, and free HL ligand. Therefore, the fluorescent emissions observed in the coordination polymers 1-3 may be ascribed to the intraligand transition of the H2PBEA ligand, since similar emissions were observed for the H2PBEA, and the reason for

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Figure 6. Emission spectra of 1-3 and H2PBEA in the solid state at room temperature.

no clear luminescence of 4 could be because of the effect of the central Mn(II) ion and bridging water molecule.22 The observed red shifts of the emission maximum between the complexes and the H2PBEA ligand are considered to mainly originate from the coordination interactions between the metal atom and the ligand.23 In addition, it is noteworthy that complexes 1-3 showed intense emissions compared with that of free H2PBEA at room temperature, which may be attributed to the strength of rigidity in the solid state.24 Conclusions Four highly connected MOFs were synthesized by the hydrothermal method with the mixed linkers: flexible carboxylate ligand H2PBEA and rigid imidazole-containing ligand HL. These four complexes are constructed based on metal clusters, which show high stability as indicated by TGA measurements. Compound 3 represents the highest-connected trinodal network topology presently known for MOFs. The single crystal X-ray diffraction analysis of 1-3 revealed that the counterions have a subtle but significant influence on the selfassembly process although the counterions are not incorporated into the structures. Complex 4 shows antiferromagnetic interaction within the binuclear Mn(II) unit. The results of the luminescence investigation showed that the Cd(II) complexes exhibited blue photoluminescence, while no emissions were observed for the Mn(II) complex. 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 nos. 2007CB925103 and 2010CB923303). Supporting Information Available: X-ray crystallographic file in CIF format, PXRD (Figure S1), TGA (Figure S2), and crystal structure and topology (Figures S3-S6). This information is available free of charge via the Internet at http://pubs.acs.org.

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