Cobalt(II) and nickel(II) coordination polymers constructed from P,P′-diphenylmethylenediphosphinic acid (H2pcp) and 4,4′-bipyridine (bipy): Structural isomerism in [Co(pcp)(bipy)0.5(H2O)2]

The P,P′diphenylmethylenediphosphinic acid (H2pcp) reacts with Co(ClO4)2 · 6H2O and 4,4′-bipyridine to give a mixture of two polymeric isomers of formula [Co(pcp)(bipy)0.5(H2O)2], {red (1) and pink (2)} and the new violet hybrid [Co(Hpcp)2] (3). The pure red and violet species have been obtained by the reaction of H2pcp with Co(CH3COO)2 · 4H2O and bipy or with Co(ClO4)2 · 6H2O, respectively. The analogous reaction of Ni(CH3COO)2 · 4H2O or Ni(ClO4)2 · 6H2O with H2pcp and bipy affords only the [Ni(pcp)(bipy)0.5(H2O)2] species (4). The two cobalt isomers present different structural arrangements. Whereas the red isomer (1) shows an undulated 2D layered structure, the pink one (2) forms an infinite monodimensional strand. Both the architectures extend to higher dimensions through hydrogen bonding interactions. The nickel derivative is isomorphous with the red cobalt isomer. The violet [Co(Hpcp)2] (3), which is isomorphous with the complexes of the reported series [M(Hpcp)2], M = Ca(II), Mg(II), presents a monodimensional polymeric structure. Compounds 1 and 4 show a very similar thermal behaviour, the two water molecules being lost in the temperature range 25–150 and 160–320 °C, respectively. Temperature dependent X-ray powder diffractometry (TDXD) has been performed on compound 1 in order to follow the structural transformations that occur during the heating process.