Helical vs. zigzag coordination polymer: influence of structural preference of metal-ion coordination geometry

Abstract

Two new coordination polymers [(L⁶)CoCl₂]_∞ (1) and [(L⁶)CdCl₂]_∞ (2) (L⁶ = α,α'-bis(pyrazolyl)-m-xylene) have been synthesized and characterized by X-ray crystallography. Structural analysis of 1 (space group P2₁) revealed that each Co(II) center is coordinated by two chloride ions and two pyrazole nitrogens from two different L⁶ ligands, giving rise to pseudo-tetrahedral coordination environment around Co(II). For this structure 1D helical polymeric chain running along crystallographic 2₁ axis is observed. While for 2 (space group ), each Cd(II) center is coordinated by two chloride ions, two pyrazole nitrogens from two different L⁶ ligands, and a chloride ion from the adjacent layer. It provides distorted trigonal bipyramidal geometry around Cd(II), which leads to the formation of a 2D zigzag polymer. In continuation of our recent activity on inorganic crystal engineering, from the standpoint of metal-ligand coordination chemistry and C-H...Cl₂M^II hydrogen bonding, in this work we have investigated the potential of coordination tectons 1 and 2 in bringing about generality in helix/zigzag network formation, strengthened primarily by C-H···Cl hydrogen-bonding interactions.