Inorganic–organic hybrid materials of p,p′-diphenylmethylenediphosphinic acid (H2pcp) with magnesium and calcium ions: Synthesis and characterization of [Mg(Hpcp)2], [Mg(Hpcp)2(H2O)4], [Mg(pcp)(H2O)3](H2O), [Ca(Hpcp)2] and [Ca(pcp)(H2O)] complexes

The p,p′-diphenylmethylenediphosphinic acid (H2pcp) reacts with Mg(SO4) or CaCl2 · 6H2O to give the anhydrous hybrid material [Mg(Hpcp)2] or [Ca(Hpcp)2]. Both the Mg and Ca derivatives, which are isomorphous, present polymeric 1D structural arrays, where the metal ions are doubly bridged by two Hpcp− ligands. When the reaction is carried out with Mg(OH)2 (or Ca(OH)2), hydrate metal complexes of the aprotic form pcp2− are obtained, namely the hybrids [Mg(pcp)(H2O)3] · (H2O) and [Ca(pcp)(H2O)]. The magnesium compound presents a hydrogen bonding 2D layered structure, where the water molecules play the important role of cementing together the 1D chains of metal ions bridged by phosphinate ligands. Differently a 2D layered architecture of the calcium derivative is built up by dimeric units of calcium metals bridged by pcp2− ligands, without the action of the water molecule, whose role is limited to stabilize the layer itself. From the mother solution affording the anhydrous [Mg(Hpcp)2] complex, the hydrate [Mg(Hpcp)2(H2O)4] can be isolated, which is a monomeric complex trapped in a closed 2D net of hydrogen bondings. The solid compounds were characterized by X-ray studies and thermogravimetric analysis.