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

摘要

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.