Copper(II) Complexes with Bridging Diphosphinates- The Effect of the Elongation of the Aliphatic Chain on the Structural Arrangements around the Metal Centres

The reactivity in water solution of the two closely related P,P'-diphenylmethylenediphosphinic (H(2)Pcp) and PP'-diphenylethylenediphosphinic (H(2)pc(2)p) acids towards copper(II) salts, in the presence of 2,2'-bipyridine, has been investigated. The reaction of H(2)pc(2)p with copper(II) acetate and 2,2'-bipy resulted in the dinuclear complex of formula [(2,2'-bipy)Cu(mu-pc(2)p)(2)Cu(2,2'-bipy)]center dot 4.5H(2)O (2), which contrasts the monomeric complex [(2,2'-bipy)Cu(pcp)(H2O)] (1) previously obtained from H(2)pcp. The reactions of H(2)pcp and H(2)pc(2)p with copper(II) perchlorate and 2,2'-bipy resulted in the two different dinuclear complexes respectively of formulas [(2,2'-bipy)(H2O)Cu(mu-pcp)(mu-ClO4)Cu(2,2'-bipy)][ClO4]center dot[(2,2'-bipy)(ClO4)Cu([mu-pcp)(mu-ClO4)Cu(2,2'-bipy)]center dot H2O (3) and [(2,2'-bipy)Cu(mu-pc(2)p)(mu-ClO4)Cu(2,2'-bipy)(ClO4)] (4). The structures of the new complexes and those of the solid diphosphinic acids H(2)Pcp and H(2)pc(2)p have been characterized by single-crystal X-ray diffraction analyses. In spite of their close similarity the two diphosphinate ligands adopt different conformations which in turn can remarkably influence the structural arrangements of the resulting copper complexes. The magnetic properties of complex 3, which contains four metal centers, with three of them in different (even if similar) chemical environments, have been characterized by low-temperature measurements.