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

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 P1¯), 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⋯Cl2MII hydrogen bonding, in this work we have investigated the potential of coordination tectons1 and 2 in bringing about generality in helix/zigzag network formation, strengthened primarily by C–H⋯Cl hydrogen-bonding interactions.

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. With invariant coordinating ligand and composition of four-/five-coordinate metal complexes (1)/(2), the nature of extended structure differs due to subtle difference in metal-ion coordination environment (from distorted tetrahedral to distorted trigonal bipyramidal). This result point towards generality in helix/zigzag network formation, which is strengthened primarily by C–H⋯Cl hydrogen-bonding interactions.Figure optionsDownload as PowerPoint slide