Influence of biphenyl spacer appended to the flexible phosphonate arms in modulating the dimensionality of the coordination polymers: Synthesis, structural chemistry and magnetic properties

Abstract

Two new compounds [Co (2,2′-bipy) (H 2dbp)] n (1) and [Ni (2,2′-bipy) 2(H 2dbp)(H 2O)] ·H 2O (2) based on the flexible ligand 4,4′- dimethylenebiphenyldiphosphonic acid (H 4dbp) with 2,2′-bipyridine as secondary ligand have been synthesized under hydrothermal conditions. Both the compounds are well characterized by routine elemental analysis, IR, electronic spectroscopies, thermogravimetric analysis and finally by single crystal X-ray diffraction analysis. Compound 1 is a 1D extended coordination polymer and 2 is a discrete molecular compound. A comparative study between the geometries of H 4dbp ligand (in compounds 1 and 2, present study) and p-xylylenediphosphonic acid (H 4pxp) ligand (in previously reported compounds [Cu(2,2′-bipy) (H 2pxp)]·nH 2O (1A) and Ni(2,2′-bipy) 2H 4pxp] n[H 2pxp] n (2A), see text) demonstrate the effect of the twisting in the benzene rings in changing higher dimensional H xpxp (x refers to number of protonated hydroxyl groups) compounds to lower dimensional H xdbp compounds. The eight membered Co-dimer rings formed in compound 1 represents the simple and isolated Co-dimer, exhibiting weak antiferromagnetic exchange between metal centers through OPO bridges. © 2012 Elsevier Inc. All rights reserved.