Influence of the counter anion and steric hindrance of pyrazolyl and imidazolyl flexible ligands on the structure of zinc-based coordination polymers

Treatments of flexible 1,4-bis(3,5-dimethylpyrazolyl)butane (bbd), 1,4-bis(imidazolyl)butane (bib) and 1,4-bis(2-methylimidazolyl)butane (bmib) ligands with zinc salts at room temperature, resulted in the formation of four novel metal–organic coordination architectures: [ZnI2(μ-bbd)]n (1), [Zn(NCS)2(μ-bbd)]n (2), {[Zn(μ-bib)2](ClO4)2·(Et2O)0.5·(H2O)0.25}n (3) and {[Zn(μ-bmib)2](ClO4)2·(H2O)4}n (4). X-ray crystallographic analyses show different 1D and 3D polymeric structures for compounds 1–4 due to the variation of the counter anions, solvent, steric hindrance and position of donating atoms in the structure of flexible ligands. In 1 and 2, one-dimensional (1D) zig-zag polymeric chains are formed via metal centers and μ-bbd ligands. Complex 3 shows a 3-fold interpenetrated 3D architecture with 103-ths network topology. In contrast to 3, in the structure of 4 neighboring Zn(II) ions are interconnected by a double-bridging μ-bmib ligands to form an infinite 1D polymeric double chain. The conformations of the flexible ligands were analyzed in detail.