Synthesis and crystal structure of a coordination polymer [Zn(p-pdoa)(bbp)]n with a one-dimensional helical chain

The coordination polymer [Zn(p-pdoa)(4)(bbP)(n) 1 (p-pdoa = p-phenylenedioxydiacetate dianion and bbp = 2,6-bis(benzimidazol-2-yl)pyridine) has been synthesized by hydrothermal method and characterized by elemental analysis, IR and X-ray single-crystal diffraction. The title complex crystallizes in the triclinic system, space group P (1) over bar with a = 7.8383(2), b = 12.6610(4), c = 13.1792(5) angstrom, alpha = 84.433(2), beta = 74.2980(1), gamma = 87.4290(1)degrees, V = 1252-93(7) angstrom(3), Z = 2, D-c = 1.593 g/cm(3), mu = 1.038 mm(-1), F(000) = 616, the final R = 0.0361 and wR = 0.1139. The Zn(II) atom assumes a distorted trigonal bipyramidal geometry, involving two carboxyl O atoms from two different p-pdoa ligands and three N atoms from the bbp ligand. The Zn(II) atom is alternately interlinked by p-pdoa ligands in a bismonodentate mode into a helical chain with a long pitch of 12.661 angstrom and the adjacent Zn center dot center dot center dot Zn distance of 11.056 and 12.245 angstrom. There exists a 2D supramolecular framework linked by pi-pi stacking (3.312 angstrom) between adjacent benzimidazoles of bbp ligands and intermolecular hydrogen-bonding interactions between the uncoordinated carboxylate oxygen atoms (O(2), O(5)) and the uncoordinated imidazolyl N atoms (N center dot center dot center dot O distances 2.706 and 2.786 angstrom). There also exist two interlayer pi-pi stacking interactions of 3.299 angstrom between adjacent central pyridines of bbp ligand and 3.176 angstrom between the phenyl groups of P-pdoa ligand. Such pi-pi stacking interactions extend the two-dimensional layers into a 3D supramolecular network.