Guang-Xiang Liu

Cadmium(II) coordination polymers with flexible tetradentate ligand 1,2,4,5-tetrakis(imidazol-1-ylmethyl)benzene: anion effect and reversible anion exchange property

Six new three-dimensional (3D) Cd(II) coordination polymers, {[Cd2(L)3](NO3)4·6H2O}n (1), {[Cd2(L)3](ClO4)4·2H2O}n (2), {[Cd2(L)3](BF4)4·2H2O}n (3), {[Cd(L)Cl2]·2H2O}n (4), {[Cd2(L)2(SO4)2(H2O)]·2H2O}n (5) and {[Cd2(L)(SO4)2(H2O)3]·4H2O}n (6), have been solvothermally synthesized by reactions of the corresponding Cd(II) salts with flexible tetradentate ligand 1,2,4,5-tetrakis(imidazol-1-ylmethyl)benzene (L), respectively. The X-ray diffraction analysis revealed that the isostructural 1, 2 and 3 have 3D framework structures with (46·66·83)2(42·63·8)3 topology. Complex 4 has a different 3D framework structure with (65·8) topology, while 5 and 6 possess pillared-layer and plywood-like 3D framework structures, respectively. The distinct structures of 1 (2, 3), 4 and 5 indicate that the counter anions with different coordination abilities play an important role in the formation of coordination polymers. Complexes 5 and 6, synthesized by the same reactants in the same solvent, have different structures due to the different metal/ligand ratio. In addition, the results also demonstrated that the flexible tetradentate ligand L can adopt varied conformations and coordination modes to form complexes with different structures. L adopts up,up,down,down-conformation in 1–3, while in 4, it has a up,down-conformation. It is interesting that two different conformations of up,down,down,up- and H-type of L coexist in 5. In the case of 6, L has H-type conformation. Furthermore, the reversible anion exchange property of 1 was studied.

Synthesis, structure and property of cobalt(II) complexes with 3,5-di(1H-imidazol-1-yl)benzoic acid

Two novel cobalt(II) complexes [Co(L)(NO3)] (1) and [Co(L)(H2O)2]ClO4 (2) were synthesized by reactions of 3,5-di(1H-imidazol-1-yl)benzoic acid (HL) with corresponding cobalt(II) salts, and their structures were determined by single crystal X-ray diffraction analysis. In the title complexes, the carboxylate group of L− ligand adopts a µ2–ŋ1:ŋ1-bridging mode to connect two cobalt(II) atoms, and each L− ligand acts as a 4-connector, and the cobalt(II) has distorted octahedral coordination geometry. In 1, one oxygen atom of the nitrate anion links two cobalt(II) atoms to complete a 3D structure which is a binodal (4,6)-connected net with Schlafli symbol of (3·42·52·6)(32·42·52·64·74·8). While in 2, the 3D structure has topology related to SrAl2, CeCu2 and KHg2 with Schlafli symbol of (42·63·8) and there are 1D channels filled with perchlorate anions. The results revealed that the nature of the counteranions, such as their shape, size and coordination ability, has a remarkable influence on the structure of the complexes. The results of the magnetic measurements showed that there are antiferromagnetic interactions between the neighboring Co(II). Furthermore, complex 2 exhibited a modest second-harmonic-generation (SHG) efficiency and anion-exchange property.

Structure diversity and reversible anion exchange properties of cadmium(II) complexes with 1,3,5-tris(imidazol-1-ylmethyl)benzene: counteranion-directed flexible ligand conformational variation

Six cadmium(II) coordination polymers, {[Cd(tib)2](BF4)2}n (1), {[Cd(tib)2](NO3)2·2EtOH}n (2) (EtOH = ethanol), {[Cd(tib)(OAc)2]·4.5 H2O}n (3) (OAc = acetate anion), {[Cd(tib)(μ2-Cl)Cl]·MeOH}n (4) (MeOH = methanol), {[Cd(tib)2(H2O)2]Cl2·4 H2O}n (5) and {[Cd(tib)2][Cd2I6]}n (6), were obtained by reactions of flexible tripodal ligand 1,3,5-tris(imidazol-1-ylmethyl)benzene (tib) with the corresponding metal salts, respectively. Their structures were determined by X-ray crystallography. Complexes 1 and 6 have infinite 2D cationic double layered structures with different shapes. Complex 2 possesses a 3D framework structure with two different kinds of channels. The structure of 3 is a two-fold interpenetrated 3D framework. Complexes 4 and 5, synthesized by the same reactants in the same solvent, have different 2D network structures due to the different synthetic methods. The distinct structures of the complexes (e.g.1, 2 and 6) indicate that the counteranions have significant influence on the structures of coordination polymers. In addition, the results also attest that the flexible ligand tib can adopt different conformations and coordination modes to form complexes with varied structures. Furthermore, the reversible anion exchange properties of 1 and 2 were studied.

Unprecedented three-dimensional 10-connected bct nets based on trinuclear secondary building units and their magnetic behavior

Three unprecedented metal-organic frameworks [M3(tib)2(CTC)2]·nH2O [M = Co(II), n = 2 (1); Mn(II), n = 2.92 (2) and Ni(II), n = 2 (3)] based on M3(OCO)6 trinuclear secondary building units (SBUs) have been successfully synthesized by reactions of corresponding metal salt with mixed flexible triacid of 1,3,5-cyclohexanetricarboxylic acid (H3CTC) and rigid imidazol-containing ligand 1,3,5-tris(1-imidazolyl)benzene (tib) under hydrothermal conditions. In 1–3, the CTC3− ligands link the SBUs to form two-dimensional (2D) ‘hxl’ (hexagonal lattice) networks and the tib ligands further pillar the 2D layers leading to the formation of three-dimensional frameworks, which are firstly reported uninodal 10-connected bct nets. The magnetic measurements showed that 1 and 3 exhibit ferromagnetic coupling interactions between the adjacent metal centers with g = 2.63, D = 66.69 cm−1, zJ = 0.68 cm−1 and g = 2.22, J = 6.25 cm−1, zj′ = −0.053 cm−1, respectively, while 2 has antiferromagnetic interaction between the Mn(II) ions with g = 2.01, J = −0.57 cm−1, zj′ = 1.3 × 10−4 cm−1.

Syntheses, crystal structures and properties of silver(I) and copper(II) complexes with an oxazoline-containing tetradentate ligand

Six new coordination complexes, [AgL]CF3SO3 (1 and 2), [Ag2L2](NO3)2·4CH3NO2 (3), [AgL]NO3·0.5CH3OH (4), [AgL]BF4 (5) and [Cu4L2(OCH3)2(OH)2(NO3)2](NO3)2·0.32H2O (6), were obtained by reactions of the corresponding metal salts with ligand N,N′-bis[4-(4,5-dihydrooxazol-2-yl)-benzyl]ethane-1,2-diamine (L). The results of X-ray crystallographic analysis indicate that complexes 1 and 2 are supramolecular isomers with a wavelike cationic two-dimensional network structure of 1 and a double-stranded helical chain of 2. Complexes 4 and 5 also have helical chain structures with P and M forms. Differing from polymeric structure of 1, 2, 4 and 5, complexes 3 and 6 are a M2L2 molecular rectangle and a M4L2 cage, respectively. The results show that the flexible ligand L can have different conformation and coordination modes leading to complexes with varying structures. Magnetic data show that there are antiferromagnetic interactions in the dimeric unit of complex 6.