Syntheses and Structural Characterization of a One-Dimensional

Syntheses and Structural Characterization of a One-Dimensional Chain, Two-Dimensional Noninterpenetrated Grid, and Three-Dimensional Polycatenane Coordination Polymers Assembled from Flexible Bidentate Imidazolyl Ligands

CRYSTAL GROWTH & DESIGN 2007 VOL. 7, NO. 10 2071-2079

Shouwen Jin,† Wanzhi Chen,*,† and Huayu Qiu*,‡ Department of Chemistry, Zhejiang UniVersity, Xixi Campus, Hangzhou 310028, P. R. China, and Key Laboratory of Organosilicon Chemistry and Material Technology of Ministry of Education, Hangzhou Teachers College, Hangzhou 310012, People’s Republic of China ReceiVed October 2, 2006; ReVised Manuscript ReceiVed June 29, 2007

ABSTRACT: Eight novel coordination polymers, [Mn(L1)2(H2O)2]Cl2‚2H2O (1, L1 ) bis(N-imidazolyl)methane), [Fe(L1)2(NCS)2] (2), [Zn(nba)2L2] (3, nba ) p-nitrobenzoate, L2 ) 1,4-bis(N-imidazolyl)butane), [Ni(L2)(hba)2(MeOH)2]‚2MeOH (4, hba ) p-hydroxybenzoate), [Cd(L2)1.5(NCS)2] (5), [Cd(L2)2(NO3)2] (6), [Cd(L2)2(tos)2] (tos ) p-tolylsulfonate, 7), and [Ni(L2)3](NO3)2 (8), were obtained from self-assembly of the corresponding metal salts with the flexible ligands, and their structures were fully characterized. X-ray diffraction analyses revealed that complexes 1 and 2 exhibit one-dimensional (1D) double-stranded chain structures resulting from doubly bridged [Mn(L1)2(H2O)2] and [Fe(NCS)2], respectively. Complexes 3 and 4 have 1D zigzag chain structures in which [Zn(nba)2] and [Ni(hba)2(MeOH)2] units are held together by L2 bridges, respectively. The polymeric cadmium complexes 5-7 have two-dimensional (2D) grid network structures with (4,4) topology. Complex 8 is a cationic polycatenane, and the nitrate anions occupy the triangular channels formed by the interpenetrating networks. Complexes 2, 3, 5, and 6 are stable up to 300 °C. Photoluminescent studies show that complexes 3 and 5-7 display intense blue emissions. Introduction Supramolecular assemblies with desirable topological networks of self-organized molecular building blocks have recently received great attention.1-3 This is due to fundamental interest in self-assembling processes,4 supramolecular motifs,5 and most significantly crystal engineering of their intriguing structure topologies. Some success has been achieved in the manufacture of coordination framework materials with solvent inclusion6,7 or gas adsorption7-9 properties, or with electronic10 and nonlinear optical properties.11 Coordination polymers have been shown to form a wide range of interesting network topologies such as honeycomb,12 brick wall,13 grid,14 ladder,15 herringbone,16 diamondoid,17 polycatenanes, and polyrotaxanes18 using a building-block methodology.19 The framework structure is primarily dependent upon the coordination preferences of the metal centers and the functionality of the ligands. Aside from coordination bonding interactions, relatively strong hydrogen bonding, π-π stacking interactions, the solvent molecules, counterions, and templates also play important roles in determining the ultimate architectures. These coordination polymers exhibit a wide range of infinite zero- to three-dimensional (3D) frameworks with different interesting structural features, resulting from coordination bonding, hydrogen bonding, and aromatic π-π stacking interactions as well as van der Waals forces.20-22 So far, a number of coordination polymers with diverse topologies have been achieved by using rigid rod-like N-donor ligands such as 4,4′-bipyridine and 4,4′-azobispyridine, which show interesting physical properties.23-26 In contrast to rigid spacers, flexible ligands, which can adopt various conformations, may induce coordination polymers with novel topologies and properties. However, flexible ligands containing N-donor ligands such as triazole27-29 and imidazole29-31 have not been well * Corresponding author: Tel & fax: +86-571-8827-3314. E-mail: [email protected]. † Zhejiang University. ‡ Hangzhou Teachers College.

studied to date. Bis(N-imidazolyl)methane (L1) and 1,4- bis(Nimidazolyl)butane (L2) can be used as flexible divergent ligands to construct coordination polymeric materials. Such coordination polymers with various metal salts have only been scarcely studied recently.32 Here in this paper we report the preparation and crystal structures of eight coordination polymers of [Mn(L1)2(H2O)2]Cl2‚2H2O (1, L1 ) bis(N-imidazolyl)methane), [Fe(L1)2(NCS)2] (2), [Zn(nba)2L2] (3, nba ) p-nitrobenzoate, L2 ) 1,4-bis(Nimidazolyl)butane), [Ni(L2)(hba)2(MeOH)2]‚2MeOH (4, hba ) p-hydroxybenzoate), [Cd(L2)1.5(NCS)2] (5), [Cd(L2)2(NO3)2] (6), [Cd(L2)2(tos)2] (tos ) p-tolylsulfonate, 7), and [Ni(L2)3](NO3)2 (8). Experimental Procedures Bis(N-imidazolyl)methane and 1,4-bis(N-imidazolyl)butane were prepared according to the reported procedures in the literature.33 All other reagents were commercially available and used as received. The C, H, and N elemental analyses were carried out with a Carlo Erba 1106 elemental analyzer. The FT-IR spectra were recorded from KBr disks in the range of 4000-400 cm-1 on a Mattson Alpha-Centauri spectrometer. Thermogravimetric analyses (TGA) were studied by a Delta Series TA-SDT Q600 in a N2 atmosphere in the temperature range between room temperature and 800 °C (heating rate ) 10 °C‚min-1) using Al crucibles. The photoluminescence study was carried out on a powdered sample in the solid state at room temperature using a Hitachi 850 spectrometer. Synthesis of Complexes. [Mn(L1)2(H2O)2]Cl2‚2H2O, 1. To an aqueous solution of disodium adipate (38 mg, 0.2 mmol), MnCl2‚2H2O (40 mg, 0.2 mmol) was added to L1 (30 mg, 0.2 mmol) in 2 mL of methanol. The solution was filtered. After the sample stood at room temperature for several days, colorless block crystals were isolated. Yield: 56 mg, 56.7%. Anal. Calcd. for C14H24Cl2MnN8O4: C, 34.02; H, 4.89; N, 22.67. Found: C, 33.98; H, 4.78; N, 22.58. IR (KBr disk, cm-1): 3459w, 3213s, 3115w, 2242w, 1632m, 1504s, 1395m, 1351w, 1284m, 1234s, 1087s, 1032w, 932m, 842m, 766m, 714m, 658m, 611w. [Fe(L1)2 (NCS)2], 2. An aqueous solution (5 mL) containing (40 mg, 0.2 mmol) of FeCl2‚4H2O was slowly added to an aqueous solution (1 mL) of NaNCS (33 mg, 0.4 mmol) to give a dark red solution. Onto

10.1021/cg060666q CCC: $37.00 © 2007 American Chemical Society Published on Web 10/03/2007

2072 Crystal Growth & Design, Vol. 7, No. 10, 2007

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Table 1. Crystal Data and Structure Refinement Summary for Compounds 1-4 1 formula Fw crystal system space group a, Å b, Å c, Å R, deg β, deg γ, deg V, Å3 Z Dcalcd Mg/m3 µ, mm-1 F(000) crystal size, mm3 θ range, deg. reflections collected reflections independent, (Rint) goodness-of-fit on F2 R indices [I > 2σI] R indices (all data)

C14H24Cl2MnN8O4 494.25 monoclinic P21/c 8.582(3) 13.450(5) 9.381(3)

2 C16H16FeN10S2 468.36 orthorhombic Cmca 9.140(3) 15.831(3) 13.961(5)

106.997(4) 1035.5(6) 2 1.585 0.935 510 0.16 × 0.14 × 0.06 2.48-25.01 5307 1824 (0.0328) 1.035 0.0378, 0.0947 0.0561, 0.1086

3 C24H22N6O8Zn 587.85 monoclinic C2/c 26.098(7) 6.5711(18) 16.638(5) 118.509(3)

2020.1(11) 4 1.540 0.979 960 0.49 × 0.40 × 0.17 2.57-24.96 5000 949 (0.0329) 1.003 0.0286, 0.0739 0.0380, 0.0851

the dark solution was layered a solution of L1 (60 mg, 0.4 mmol) in methanol (5 mL). Dark crystals suitable for X-ray diffraction were obtained after several days. Yield: 30 mg, 32%. Anal. Calcd for C16H16FeN10S2: C, 41.03; H, 3.44; N, 29.91. Found: C, 40.96; H, 3.36; N, 29.83. IR (KBr disk, cm-1): 3445w, 3127m, 3094m, 2066s, 1623w, 1494m, 1386m, 1276m, 1229s, 1086s, 1024w, 934m, 851m, 752m, 708m, 660m, 616w. [Zn(nba)2L2], 3. To an ethanol solution of zinc acetate dihydrate (22 mg, 0.1 mmol) was added p-nitrobenzoic acid (33 mg, 0.2 mmol) with stirring, and then a solution of L2 (19.9 mg, 0.1 mmol) in 2 mL of ethanol was added. A white precipitate was formed after refluxing for 30 min; the addition of 0.5 mL of conc. ammonia led to a clear solution. The solution was filtered into a test tube. After the sample stood at room temperature for several days, colorless block crystals were obtained. Yield: 50 mg, 85%. Anal. Calcd. for C24H22N6O8Zn: C, 49.03; H, 3.77; N, 14.29. Found: C, 48.85; H, 3.71; N, 14.37. IR (KBr disk, cm-1): 3446w, 3135w, 1630s, 1591s, 1515s, 1370w, 1342s, 1238w, 1098m, 952w, 877w, 831m, 797w, 724m, 654w, 618w, 525w. [Ni(L2)(hba)2(MeOH)2]‚2MeOH, 4. A solution of Ni(Ac)2‚2H2O (24 mg, 0.1 mmol) in methanol (2 mL) was added to p-hydroxybenzoic acid (28 mg, 0.2 mmol) with stirring, and then L2 (19 mg, 0.1 mmol) in methanol (3 mL) was added to give a pale blue solution. The solution was filtered. Pale blue crystals were separated from the solution after standing overnight. The product was collected, washed with water, and dried. Yield: 46 mg, 70.6%. Anal. Calcd. for C28H40N4NiO10: C, 51.63; H, 6.19; N, 8.60%. Found: C, 51.56; H, 6.14; N, 8.52%. IR (KBr disk, cm-1): 3455m, 3133w, 2947w, 2790w, 2681w, 1603s, 1535s, 1448w, 1387s, 1249s, 1170m, 1141w, 1108m, 1032w, 944m, 863m, 829m, 791w, 744w, 702m, 659m, 627m, 566m, 453m. [Cd(L2)1.5(NCS)2], 5. Cd(OAc)2‚2H2O (27 mg, 0.1 mmol) in methanol (3 mL) was added to NaNCS (16.2 mg, 0.2 mmol) in methanol (2 mL). The solution was then treated with L2 (38 mg, 0.2 mmol) in methanol (5 mL), and a white precipitate was produced immediately. The resulting white precipitate was dissolved again by adding 0.5 mL of ammonia to give a clear solution. The solution was filtered and stood at room temperature. Colorless block crystals were obtained through slow evaporation of the solution. Yield: 26 mg, 50.6%. Anal. calcd. for C17H21CdN8S2: C, 39.73; H, 4.12; N, 21.80%. Found: C, 39.79; H, 4.14; N, 21.74%. IR (KBr disk, cm-1): 3746w, 3446w, 3113w, 2936w, 2100s, 2065s, 1632, 1516m, 1449w, 1361w, 1280w, 1236w, 1111m, 1087m, 934w, 823w, 767w, 730w, 658m, 625w, 464w. [Cd(L2)2(NO3)2], 6. A solution of Cd(NO3)2‚4H2O (38 mg, 0.121 mmol) in methanol (3 mL) was added to L2 (70 mg, 0.373 mmol) in methanol (5 mL) to immediately give a white precipitate. The precipitate was dissolved by adding 2 mL of CH3CN. The solution was filtered and stood at room temperature for several days, and colorless block crystals were obtained. Yield: 30 mg, 40.2%. Anal. Calcd. for C20H28CdN10O6: C, 38.94; H, 4.57; N, 22.70. Found: C, 38.87; H, 4.50; N,

2507.3(12) 4 1.557 1.041 1208 0.48 × 0.43 × 0.29 1.78-25.00 6118 2196 (0.0315) 1.025 0.0489, 0.1247 0.0600, 0.1356

4 C28H40N4NiO10 651.35 triclinic P1h 8.514(5) 9.242(5) 10.409(5) 89.302(6) 76.287(6) 86.998(6) 794.6(7) 1 1.361 0.670 344 0.33 × 0.29 × 0.08 2.01-25.02 4139 2754 (0.0228) 1.041 0.0411, 0.0888 0.0583, 0.0991

22.64%. IR (KBr disk, cm-1): 3444w, 3122w, 2939w, 2362w, 1621w, 1513m, 1383s, 1230m, 1109m, 1084m, 1035m, 929w, 834m, 742m, 660m, 624w. [Cd(L2)2(tos)2], 7. To an aqueous solution of sodium p-toluenesulfonate (77.4 mg, 0.4 mmol), Cd(Ac)2‚2H2O (54 mg, 0.2 mmol) was added. Then the mixture was treated by L2 (38 mg, 0.2 mmol) solution in 2 mL of methanol. A white precipitate was formed immediately, and the precipitate was dissolved again by adding 2 mL of ammonia. After the sample stood at room temperature for several days, colorless block crystals were isolated. Yield: 110 mg, 65.8%. Anal. Calcd. for C34H42CdN8O6S2: C, 48.89; H, 5.07; N, 13.41. Found: C, 48.82; H, 5.02; N, 13.33. IR (KBr disk, cm-1): 3072 (br), 2091w, 1837w, 1702w, 1598w, 1456m, 1176s, 1126m, 1036s, 1010s, 814m, 707w, 685s, 568s. [Ni(L2)3(NO3)2], 8. Ni(NO3)2‚6H2O (34 mg, 0.116 mmol) in methanol (5 mL) was added to L2 (60 mg, 0.314 mmol) in methanol (20 mL). Pale blue crystals were separated from the solution after it was left overnight. The product was filtered, washed with water, and dried. Yield: 49 mg, 62.1%. Anal. Calcd. for C30H42N14NiO6: C, 47.82; H, 5.62; N, 26.03%. Found: C, 47.81, H, 5.74, N, 25.96%. IR (KBr disk, cm-1): 3458m, 3117m, 2942w, 1631w, 1522m, 1460w, 1382s, 1281w, 1239m, 1098w, 1038m, 938w, 836w, 770w, 667w, 637w. X-ray Crystallography. Single-crystal X-ray diffraction data for complexes 1-8 were collected at 298(2) K on a Siemens Smart/CCD area-detector diffractometer with a Mo KR radiation (λ ) 0.71073 Å) by using an ω-2θ scan mode. Data collection and reduction were performed using the SMART and SAINT software.34 The structures were solved by direct methods, and the non-hydrogen atoms were subjected to anisotropic refinement by full-matrix least-squares on F2 using SHELXTXL package.35 Hydrogen atom positions for all of the structures were calculated and allowed to ride on their respective C atoms with C-H distances of 0.93-0.97 Å and Uiso(H)) ) -1.2Ueq(C). Hydrogen atoms bound to water molecules or N atoms were located in the Fourier difference map, and their distances were fixed. Further details of the structural analysis are summarized in Table 1 and 2. Selected bond lengths and angles for complexes 1-8 are listed in Table 3. Crystallographic data for the structural analysis were deposited with the Cambridge Crystallographic Data center, CCDC nos. 615379 for 1, 615377 for 2, 615378 for 3, 621563 for 4, 609758 for 5, 609759 for 6, 621562 for 7, 609757 for 8. Copies of this information may be obtained free of charge from the +44(1223)336-033 or e-mail: [email protected] or URL: http://www.ccdc.cam.ac.uk.

Results and Discussion Crystal Structure Description. One-Dimensional Polymeric Double-Stranded Chain Architectures of [Mn(L1)2(H2O)2]Cl2‚2H2O (1) and [Fe(L1)2(NCS)2] (2). Complex 1 was prepared by reacting MnCl2‚2H2O with L1 in the presence of disodium adipate; however, the adipate anions are not involved

3D Polycatenane Coordination Polymers

Crystal Growth & Design, Vol. 7, No. 10, 2007 2073

Table 2. Crystal Data and Structure Refinement Summary for Compounds 5-8 5 formula fw crystal system space group a, Å b, Å c, Å R, deg β, deg γ, deg V, Å3 Z Dcalcd Mg/m3 µ, mm-1 F(000) crystal size mm3 θ range, deg reflections collected Rreflections independent, Rint goodness-of-fit on F2 final R indices [I > 2σI] R indices (all data)

C17H21CdN8S2 513.94 triclinic P1h 8.681(8) 8.861(9) 14.809(14) 105.630(13) 103.226(12) 91.186(13) 1063.8(18) 2 1.605 1.243 518 0.45 × 0.21 × 0.17 2.40-25.01 4745 3250 (0.0843) 1.036 0.0960, 0.2351 0.1288, 0.2573

6 C20H28CdN10O6 616.92 monoclinic P21/c 8.1530(16) 17.810(4) 9.0426(18) 110.93(3) 1226.4(4) 2 1.671 0.949 628 0.43 × 0.27 × 0.23 3.11-25.99 10462 2395 (0.0134) 1.039 0.0561, 0.1561 0.0608, 0.1610

in the complex, and the Cl- ions exist as free counter-anions. The coordination geometry around the Mn(II) atom was a distorted octahedron with N4O2 binding set, and Mn ion is located at the inversion center (1/2, 1, 1/2). Each Mn atom is coordinated by four imidazolyl nitrogen atoms from four individual L1 ligands and two water molecules in a trans arrangement with the cis coordination angles varying from 86.07(9)° to 93.93(9)°. The Mn-N distances range from 2.262(3) to 2.276(2) Å, which is within the range expected for such species. The structure of complex 1 consists of a onedimensional (1D) cationic double chain, and the Mn ions are linearly arranged along the crystallographic c-axis (Figure 1a). The distance between two doubly bridged Mn atoms is 9.381 Å, equal to the c length of the cell unit, whereas the shortest Mn‚‚‚Mn distance is 8.582 Å, equal to the a length of the cell unit. Such 1D chains run parallel to each other in the extended lattice. [Mn(L2)2(H2O)2]+ chains, Cl- anions, and lattice water molecules are involved into strong hydrogen bonding and thus yield 3D structure. Interestingly, it is observed that the coordinated water, free water molecules, and chloride ions form hexagonal channels running along the crystallographic b-axis, which host the [Mn2(L2)2] units. A projection view of the network structure is illustrated in Figure 1b. The O‚‚‚Cl contacts arising from hydrogen bonding are in the range of 3.090(2)3.292(4) Å, and these hydrogen bonds play an important role in stabilizing the 3D structure. Compound 2 was easily isolated from the reaction mixture of FeCl2, NaSCN, and bis(N-imidazolyl)methane. An ORTEP plot of the asymmetric unit is represented in Figure 2a, and relevant information of the bond lengths and angles is given in Table 3. [Fe(L1)2(NCS)2] crystallizes in the space group Cmca. The asymmetric unit contains one-fourth formula contents, and the full coordination sphere of the Fe(II) ion is generated by the inversion center at Fe. The Fe ion is at a special position (1, 1, 0) with an occupation factor of 0.25. Fe(II) is coordinated to four nitrogen atoms belonging to four imidazolyl ligands. The Fe-Nimidazolyl bond length is 2.203(2) Å, which is comparable to the reported complexes in the range of 2.112(1)-2.247(1) Å.38 Thiocyanate ions are N-coordinated and located in the two axial positions with an Fe-N distance of 2.156(3) Å, slightly longer than those for [Fe(btr)2(NCS)2]‚H2O (2.125(3) Å) (btr ) 4,4′-bis-1,2,4-triazole).39 The structure of complex 2 consists of linear chains extending along the [100] crystallographic direction. Similar coordination

7 C34H42CdN8O6S2 835.28 triclinic P1h 8.252(18) 9.674(19) 11.76(2) 99.71(5) 97.52(4) 104.18(5) 882(3) 1 1.572 0.795 430 0.26 × 0.15 × 0.11 1.79-25.01 4468 3020 (0.0345) 1.054 0.0583, 0.1543 0.0750, 0.1702

8 C30H42N14NiO6 753.49 trigonal R3h 13.854(2) 13.854(2) 17.222(3)

2862.6(8) 3 1.311 0.567 1188 0.34 × 0.22 × 0.13 3.55-25.01 4227 1080 (0.0562) 1.020 0.0724, 0.1898 0.1129, 0.2323

motifs have been also observed for 1,2-bis(4-pyridyl)ethane,40 4,4′-bipyridine41 bridged Fe(NCS)2 compounds. The intrachain distance between metallic ions [9.140(3) Å], the same as the dimension of the cell length of a-axis, is shorter than the one found in similar 1D compounds of Fe(II) where the metallic ions are bridged by 1,2-bis(4-pyridyl)ethane,40 4,4′-bipyridine.41 On the other hand, the Fe-Fe interchain distance along the c-axis [8.344(2) Å] is shorter than the intrachain distance. The adjacent chains are parallel to each other. The infinite chains are arranged in such a way that the linear [Fe(SCN)2] units are located below and above the centers of the macrocylic rings formed by two Fe atoms and two bis(N-imidazolyl)methane ligands. A projected view showing the alignment of the [Fe(L1)2(NCS)2]chains is depicted in Figure 2b. One-Dimensional Polymeric Zigzag Chain Architectures of [Zn(nba)2L2] (3) and [Ni(L2)(hba)2(MeOH)2]‚2MeOH (4). As shown in Figure 3a, in [Zn(nba)2(L2)] (nba ) p-nitrobenzoate, 3) the zinc(II) atom displays a tetrahedral coordination environment and is coordinated by two N atoms from two different L2 ligands and two oxygen atoms of p-nitrobenzoate anions. The Zn-N bond distance is 2.008(3) Å, and the N-Zn-N angle is 105.41(17)°, which are similar to those of other known Zn complexes.36 p-Nitrobenzoate anions coordinate to Zn atom in a monodentate fashion. N-Bis(imidazolyl)methane acts as a bidentate bridging ligand and holds the [Zn(nba)2] units together to generate a 1D zigzag chain structure extended along the c-axis (Figure 3b). Interestingly, it is observed that the Zn atoms in a single chain are situated in two perfectly linear lines parallel to the crystallographic c-axis, and the distances between alternate Zn atoms are 6.571 Å, whereas the Zn-Zn distances bridged by L2 are 8.719 Å. The Zn‚‚‚Zn‚‚‚Zn angles are 107°, close to the ideal angle of a tetrahedron. The zigzag chains are strictly arranged along the Zn‚‚‚ Zn‚‚‚Zn axis (crystallographically c-axis) in a parallel way. The chains further interact via π-π stacking between phenyl rings of neighboring chains, and thus form a two-dimensional (2D) grid structure. The closing contact between the phenyl rings is 3.563 Å. The repeated stacking of the grids perpendicular with respect to the orientation of the chains results in the formation of channels along the crystallographic b-axis, shown in Figure 3c. The crystal structure of 4 consists of [Ni(L1)(hba)2(MeOH)2]‚ 2MeOH (hba ) p-hydroxybenzoate) unit and two free methanol molecules. The asymmetric unit contains only a half of its


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Table 3. Selected Bond Lengths [Å] and Bond Angles [°] for 1-8a Mn(1)-O(1) Mn(1)-N(4) O(1)-Mn(1)-N(2)#1 O(1)-Mn(1)-N(4)#1 N(2)-Mn(1)-N(4)#1

2.203(2) 2.276(2) 88.49(9) 88.84(9) 86.07(9)

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

2.262(3) 180.0 91.51(9) 93.93(9) 91.16(10)

2 Fe(1)-N(3) #1 N(3)-Fe(1)-N(3)#1 N(2)#1-Fe(1)-N(2)#2 N(3)-Fe(1)-N(2)#3

2.156(3) 180.00(15) 93.14(10) 89.94(7)

Fe(1)-N(2) #2 N(3)-Fe(1)-N(2)#1 N(2)#2-Fe(1)-N(2)

2.2033(18) 90.06(7) 86.86(10)

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

2.008(3) 124.60(12) 105.41(17)

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

2.079(2) 180.0 88.82(8) 91.86(8) 90.70(8) 180.0

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

1.995(3) 92.43(18) 105.71(12)

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

4 2.042(2) 2.1401(19) 91.18(8) 180.0 88.14(8) 89.30(8)

Cd(1)-N(8) Cd(1)-N(3) Cd(1)-N(7)#1 S(1)-C(16) N(8)-Cd(1)-N(1) N(1)-Cd(1)-N(3) N(1)-Cd(1)-N(5) N(8)-Cd(1)-N(7)#1 N(3)-Cd(1)-N(7)#1 N(8)-Cd(1)-S(1) N(3)-Cd(1)-S(1) N(7)#1-Cd(1)-S(1)

2.306(11) 2.328(9) 2.336(11) 1.648(14) 90.0(4) 177.0(4) 83.8(3) 96.0(5) 90.7(4) 176.1(4) 90.3(3) 87.6(3)

5

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

Cd(1)-N(1) Cd(1)-N(5) Cd(1)-S(1) S(2)-C(17) N(8)-Cd(1)-N(3) N(8)-Cd(1)-N(5) N(3)-Cd(1)-N(5) N(1)-Cd(1)-N(7)#1 N(5)-Cd(1)-N(7)#1 N(1)-Cd(1)-S(1) N(5)-Cd(1)-S(1)

6 2.301(4) 2.405(6) 1.301(9) 180.0 90.78(14) 95.7(2) 81.71(18) 81.71(18)

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

2.307(10) 2.333(10) 2.840(4) 1.639(13) 88.2(4) 88.9(4) 93.8(4) 91.9(4) 173.4(4) 91.4(3) 87.6(3)

2.345(4) 1.193(8) 1.185(8) 89.22(14) 180.0 84.3(2) 98.29(19) 180.0

Figure 1. (a) Local coordination environment around the Mn atom in 1. (b) Hexagonal windows arising from the hydrogen bonding interaction bewteen the 1D cationic double chains and water molecules viewed down the a-axis.

7 Cd(1)-N(3)#1 Cd(1)-O(1)#1 N(3)-Cd(1)-N(1) N(1)-Cd(1)-N(1)#1 N(3)#1-Cd(1)-O(1)

2.280(6) 2.411(5) 88.6(2) 180.0 89.3(2)

Ni(1)-N(1) #1 N(1)#1-Ni(1)-N(1)#2 N(1)#1-Ni(1)-N(1)#4 N(1)#4-Ni(1)-N(1)#5

2.123(4) 91.78(17) 88.22(17) 179.998(1)

Cd(1)-N(1)#1 N(3)-Cd(1)-N(3)#1 N(3)#1-Cd(1)-N(1) N(3)-Cd(1)-O(1) N(1)-Cd(1)-O(1)

2.344(6) 180.0(2) 91.4(2) 90.7(2) 84.4(2)

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

1.240(14) 180.0 180.0

8

a Symmetry codes for 1: #1 -x + 1, -y, -z + 1. for 2: #1 -x + 2, -y + 2, -z; #2 x, -y + 2, -z; #3 -x + 2, y, z. for 3: #1 -x + 1, y, -z + 3/2. for 4: #1 -x + 1, -y + 1, -z + 1. for 5: #1 -x + 2, -y, -z + 1. for 6: #1 -x, -y + 1, -z + 1. for 7: #1 -x + 1, -y + 1, -z + 1. for 8: #1 x - y + 1/3, x - 1/3, -z + 2/3; #2 -x + 4/3, -y + 2/3, -z + 2/3; #3 -x + y + 1, -x + 1, z; #4 -y + 1, x - y, z; #5 y + 1/3, -x + y + 2/3, -z + 2/3.

formula content with Ni atom at the inversion center. As shown in Figure 4a, the coordination geometry around the nickel(II) atom is a slightly distorted octahedron with N2O4 binding set. Each Ni atom is coordinated by two imidazolyl nitrogen atoms from two individual L1 ligands, two p-hydroxybenzoate anions, and two methanol molecules in which the same ligands are positioned in a trans arrangement. p-Hydroxybenzoate anions coordinate to the Ni atom in a monodentate fashion. The two imidazolyl rings and the two p-hydroxybenzoate anions con-

Figure 2. (a) Local coordination environment of iron(II) in 2 with the atomic numbering scheme. (b) Packing diagram of 2 viewed along the b-axis.

stitute the equatorial plane, whereas the two MeOH molecules are located at the axial positions. The Ni(1)-N and Ni-O bond distances are 2.079(2) and 2.042(2) Å, respectively, which are comparable to the those of known complexes.37 The fact that the Ni-Ocarboxylate bond distance was shorter than the Ni-



Figure 4. (a) Local coordination environment around the Ni atom in 4. The atoms are drawn with 30% probability ellipsoids. (b) The arrangement of the 1D wavy chains of 4 viewed down the c-axis. Hydrogen bonds are not shown for clarity. Figure 3. (a) Local coordination environment around the Zn atom in 3. The atoms are drawn with 30% probability ellipsoids. (b) Onedimensional zigzag chain structure of 3 extended along the c-axis. (c) Illustration of the channels along the b-axis.

Omethanol bond distance (2.134(2) Å) indicates that the oxygen atom of p-hydroxybenzoate coordinated more strongly to the central metal than to the oxygen atom of methanol. This supramolecular structure of 4 can be best described as follows: first, the Ni ions are connected by an imidazolyl ligand to give an infinite 1D wavy chain due to the flexible conformation of 1,4-bis(N-imidazolyl)butane, as depicted in Figure 4b. The intrachain Ni‚‚‚Ni separations are 10.409 Å, whereas the shortest interchain Ni‚‚‚Ni distance is 8.514 Å. The chains are spatially separated by the outstretched p-hydroxybenzoate arms. Then, the chains interact with each other through weak secondary bonding forces. The hydroxyl groups of p-hydroxybenzoate are not involved in the coordination sphere but form strong hydrogen bonds with the coordinated and free MeOH molecules, which result in a 3D framework. The three shortest hydrogen bonds are O(5)-H(5)‚‚‚O(2)#1 (2.765(3) Å, 168.5°), O(4)-H(4)‚‚‚O(2)#2 (2.612(3) Å, 162.0°), and O(3)-H(3)‚‚‚ O(5)#3 (2.655(3) Å, 173.7°) (#1 -x + 1, -y + 1, -z + 2; #2 -x + 1, -y + 1, -z + 1; #3 -x + 1, -y, -z + 2). Except for the linkage of hydrogen bonds, the weak π-π interaction of the phenyl rings also makes a contribution to the stabilization of the 3D structure. The most interesting feature of complex 4 is that its 3D network consists of 1D channels along the c-axis.

Polymeric Square-Grid Architectures of [Cd(L2)1.5(NCS)2] (5), [Cd(L2)2(NO3)2] (6), and [Cd(L2)2(tos)2] (7). When ligand L2 reacted with cadmium(II) thiocyanate in situ, crystals of compound 5 suitable for X-ray analysis were successfully isolated. The asymmetric unit of 5 consists of one cadmium(II) atom, two thiocyanate ions, and one-and-a-half 1,4-bis(Nimidazolyl)butane. Figure 5a exhibits the crystal structure of 5 together with the atom numbering scheme. Each Cd atom is coordinated with one SCN- sulfur atom, two SCN- nitrogen atoms, and three imidazolyl nitrogen atoms completing its distorted octahedral geometry. Each pair of the same donating atoms is in a trans configuration. The cadmium(II) atom is at the center of symmetry, which is 5N/1S hexacoordinated, as depicted in Figure 5a. Cadmium(II) atoms are bridged by two SCN- ions: one of them is S-coordinated, the second is N-coordinated to the same side of the metal atom, and another one is monodentately N-coordinated to another side of the metal atom, thus forming an infinite linear chain structure. The CdNimidazolyl and Cd-NNCS bond distances being in the range of 2.306(11)-2.336(11) Å are similar to those of our previously reported cadmium compounds.42 The Cd(1)-S(1) bond distance is 2.840(4) Å, longer than those of the known reported complexes.42 The bond angle C(17)-N(8)-Cd(1) is 172.0(11)°, which deviates from a linear configuration. Unlike most of the [Cd(SCN)2L2] (where L ) 2-, 3-, or 4-methylpyridine) complexes,43 which show infinite zigzag chain alignment, the spatial arrangement of Cd in 5 exhibits a


Figure 5. (a) X-ray crystal structure of complex 5 with atom numbering scheme. The thermal ellipsoids are drawn at 30% probability. (b) Infinite 2D grid structure. (c) Packing diagram of the grid sheet showing the channels along the crystallographic b-axis.

2D grid structure (Figure 5b). It is noted that two kinds of rectangular grids exist that are alternately connected. One is formed by four 1,4-bis(N-imidazolyl)butane and four Cd ions with a dimension of 8.681 × 8.681 Å, and another one constitutes two thiocyanate, two 1,4-bis(N-imidazolyl)butane, and four Cd ions with a dimension of 6.020 × 8.681 Å based on the metal-metal distances. The grid sheets stack approximately along the crystallographic b-axis to form 1D channels. The sheets stack repeatedly in such a way that the cadmium ions of one layer are located below and above the cadmium atoms of the second layer that results in the formation of microchannels (Figure 5c). When the reaction of ligand L2 with cadmium(II) nitrate was carried out in a mixed methanol and acetonitrile solution, compound 6 with a different grid structure was obtained. X-ray crystallographic analysis shows that the cadmium(II) atom in complex 6 is six-coordinated. Four crystallographically equivalent ligands of L2 are situated in a square planar fashion about the Cd center; two crystallographically equivalent nitrate ions occupy the axial positions. Both nitrate anions act as monodentate ligands (Figure 6a). The Cd-N lengths of 2.346(2) and

Jin et al.

Figure 6. (a) Local coordination environment of metal atom in 6 with the atomic numbering scheme. (b) Infinite 2D grids structure of 6. (c) Rhombic grids of 6 stack along the crystallographic c-axis in a crossover fashion.

2.301(2) Å are longer than those found for [CdL21.5(H2O)2(SO4)]‚4H2O.32c The equatorial Cd-N bond lengths are shorter than the axial Cd-O bond lengths. Thus, the coordination geometry of cadmium(II) can be best regarded as a slightly distorted octahedron. The bond distances between the cadmium(II) atom and the two oxygens are 2.406(4) Å, which are similar to those in [CdL21.5(H2O)2(SO4)]‚4H2O.32c The polymeric structure of 6 generated from such coordination consists of 2D square-grid-type layers extended at the crystallographic ab plane with inner square cavity dimensions of 9.043 × 9.043 Å2. Each square grid is composed of four Cd ions connected through four 1,4-bis(N-imidazolyl)butane ligands. These grids repeat to give an infinite 2D network (Figure 6b). Quite unlike compound 5, the rhombic grids stack along the crystallographic c-axis in such a way that the metal atoms of the next grid sheet are situated above and below the grid centers and thus reduce the size of accessible channels (Figure 6c). In complex 7, the Cd atom is surrounded by four nitrogen


Figure 7. (a) Coordination environment around the Cd atom in 7. The atoms are drawn with 30% probability ellipsoids. (b) 2D square grid structure of 7.

atoms of four different L1 and two oxygen atoms of two p-tolylsulfonate anions completing the octahedron environment. Both p-tolylsulfonate anions act as monodentate ligands (Figure 7a). The bond lengths Cd-N are 2.344(6) and 2.279(6) Å, which are consistent with those of the previously reported [CdL21.5(H2O)2(SO4)]‚4H2O (2.264(5)-2.280(5) Å).32c The bond distance of Cd-O is 2.411(5) Å, similar to those in [CdL21.5(H2O)2(SO4)]‚4H2O.32c The most striking feature of compound 7 is that the four crystallographically equivalent L2 ligands located at the equatorial plane are connected through [Cd(tos)2] units and yield 2D grid sheets. Each large square grid has a dimension of 9.674 × 9.674 Å and are enclosed by four ligands and four Cd(II) atoms as depicted in Figure 7b. The square-grid layers are strictly flat with coordinated p-tolylsulfate ions located below and above the plane, and the grid sheets are separated by the anions. Two adjacent square grid layers lie over one another so that the p-tolylsulfonate anions are positioned over the centers of square grids of the next layer. Similar to compound 6, such stacking reduces the dimensions of the channels formed by stacking the grid sheets. A number of square-grid coordination polymers have been reported, since these materials are expected to be useful as porous materials such as gas storage and molecular recognition. Although many grid coordination polymers can have large grid dimensions, the grid sheets stacking often reduce the accessible channel size. Among the known square-grid polymers, many are achieved by using rigid bipyridyl ligands. It is believed that the flexible ligands will favor the formation of interpenetrating


Figure 8. (a) X-ray crystal cationic structure of complex 8. The thermal ellipsoids are drawn at 30% probability. (b) A project view of the 3D interpenetrated network structure viewed down the crystallographic c-axis.

multidimensional structures; thus the construction of squaregrid coordination polymers by using non-rigid ligands has been only scarcely explored. The successful preparation and characterization of three cadmium coordination polymers having 2D grid architectures illustrate that the suitable flexible bifunctional ligands are also applicable. Such coordination polymers may be expected to have unique properties that are not found for the materials based on rigid ligands. 3D Polymeric Network Structure of [Ni(L2)3](NO3)2, 8. Complex 8 was prepared by the reaction of a methanol solution of Ni(NO3)2‚6H2O and L2 in a 1:3 ratio. Elemental analysis suggests the composition of [Ni(L2)3](NO3)2, which was further confirmed by X-ray single-crystal structural analysis. X-ray crystallographic analysis showed that complex 8 is a polycatenane. Six L2 ligands are wrapped around the nickel(Π) ion to give an octahedral coordination geometry that possesses a crystallographic R3h symmetry passing through the central ion. Each ligand links two Ni(II) ions, thus generating a starlike structure as shown in Figure 8a. Compound 8 exhibits 3D polycatenane network structure in which each Ni(II) ion links six metal ions via six crystallographically equivalent 1,4-bis(N-imidazolyl)butane. The compound is made of interlocking macrocycles composing four Ni(II) ions and four 1,4-bis(N-imidazolyl)butane. In this case, the metal atoms define the edges of a rhombic grid, and the Ni(II)‚‚‚Ni(II) distance through the 1,4-bis(N-imidazolyl)butane bridge is 9.845 Å, shown in Figure 8b. The closest nonbridged Ni(II)‚‚‚Ni(II) distances are 13.854 Å. The nitrate anions are located in the triangular channels formed by the interpenetrating networks running along the crystallographic c-axis. Similar


interpenetrating networks have been reported for Zn, Cd, and Co complexes constructed from bis(imidazole) ligands.44,45 Thermogravimetric Analyses. Thermogravimetric analyses (TGA) have been performed on complexes 1-8 by heating each complex to 800 °C under flowing N2 at 10 °C/min. The TGA studies showed that complexes 2, 3, 5, and 6 are stable up to 300 °C, whereas 1, 4, 7, 8 are less stable and decompose at not more than 200 °C. At 335 °C, the complex 3 begins decomposition violently with the evolution of CO2. For complex 4, the first weight loss of 9.54% (calcd 9.82%) from 72 to 97.5 °C corresponds to the release of two free methanol molecules. Further decomposition occurred at 258-327 °C with the weight loss of 59.27% (calcd 60.03%) attributing to the loss of one p-hydroxybenzoate, two coordinated methanol molecules, and one L1 molecule. The first weight loss of 12.67% (calcd 14.56%) for 1 corresponds approximately to the liberation of four water molecules below 90 °C, and the second weight loss of 44.22% (calcd. 44.31%) arises from the loss of one L1 molecule and two chloride anions from 304.8 to 353.9 °C. The weight loss of 63.97% (calcd. 63.20%) corresponding to the loss of two L1 molecules was observed for 2 from 358.4 to 384.2 °C. Complex 5 began its decomposition from 340 °C, and the weight loss of 55.13% (calcd. 55.45%) was found because of the loss of oneand-a-half L1 molecules in the range of 340.8-370.3 °C. For 6, the weight loss of 39.25% in the range of 348.7-362.5 °C is assigned to the loss of one L1 molecule and one nitrate anion, which is in agreement with the calculated value (calcd 40.85%). Complex 7 began decomposition at 225.7 °C, and there is a sharp weight loss between 418 and 482 °C. Complex 8 was observed to decompose at 286.9 °C where the framework structure began to collapse. Emission Properties. Complexes 3 and 5-7 in the solid state at room temperature are emissive. Emssion spectrum of 3 displays strong blue emissions at 429, 453, and 470 nm, and the maximum peak occurs at 470 nm upon excitation at 220 nm. Complex 5 has a broad-band fluorescent emission with peaks centered at 399, 452, and 469 nm, respectively, upon excitation at 289 nm. Such emission behaviors can be assigned to intraligand fluorescence, based on the comparisons of these band features with reported emission spectra of known Zn and Cd complexes with N-donor ligands.46 Compounds 6 and 7 have nearly identical strong blue emissions at around 430 cm-1 in their solid states upon excitation at 355 and 371 nm, respectively. These emissions also resulted from the intraligand chargetransfer processes. The photoluminescent properties of a number of d10 metal coordination polymers have been widely studied, and their luminescence behaviors are closely associated with the central metal ions and the ancillary ligands. The emission properties may be tuned via variation of ancillary ligands; thus the coordination polymers of d10 metals can be expected to be excellent candidates for blue-fluorescent materials. Summary The self-organization of designed molecules containing certain kinds of coordinating units has stimulated new efforts in the material sciences. Such crystal manipulations, often known through crystal engineering, are performed to yield arrays of controlled superstructures that provide new functional molecular solids. The successful preparation of the eight different complexes described in this paper provides a valuable approach for the construction of various coordination polymers with different structures by using suitable flexible ligands. This work demonstrates that the biimidazole ligand with a flexible spacer is capable of coordinating to metal centers with both imidazolyl

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nitrogen atoms to result in novel 1D to 3D coordination polymers. All the compounds are thermally stable, and complexes 3 and 5-7 may be suitable candidates for bluefluorescent materials. Acknowledgment. We are grateful for financial support from the National Science Foundation of China (No. 20572096) and the Zhejiang Provincial Science Foundation (No. R405066) for financial support. Supporting Information Available: Structural parameters for 1-8 as CIF files. Thermographic curves of 1-8, emission spectra, and PXRD of 3 and 5-7. This material is available free of charge via the Internet at http://pubs.acs.org.

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