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

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The P, P′diphenylmethylenediphosphinic acid (H 2pcp) reacts with Co(ClO 4) 2 · 6H 2O and 4,4′-bipyridine to give a mixture of two polymeric isomers of formula [Co(pcp)(bipy) 0.5(H 2O) 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 H 2pcp with Co(CH 3COO) 2 · 4H 2O and bipy or with Co(ClO 4) 2 · 6H 2O, respectively. The analogous reaction of Ni(CH 3COO) 2 · 4H 2O or Ni(ClO 4) 2 · 6H 2O with H 2pcp and bipy affords only the [Ni(pcp)(bipy) 0.5(H 2O) 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.