A structural study of alkaline earth metal complexes of (dichloromethylene)bisphosphonic acid P-morpholinium- and P-pyrrolidinium-P′-methyl esters

Abstract

Three alkaline earth metal complexes, [Mg(CH₃PO₃CCl₂PO₂NC₄H₈O)(H₂O)₃]_n (1), [Ba(CH₃PO₃CCl₂PO₂NC₄H₈O)(H₂O)₂]_n (2) and [Sr₂(CH₃PO₃CCl₂PO₂NC₄H₈)₂(H₂O)_3.5]_n (3), were prepared and structurally characterized in a study of the complexing properties of amide ester derivatives of (dichloromethylene)bisphosphonic acid, and their crystal structures were determined. All three compounds are coordination polymers. Compounds 1 and 2 consist of 1D chains. In 1, the chains contain two independent octahedral Mg atoms in special positions, connected by L₁ ligands, L₁ = (Cl₂CP₂O₅MeNC₄H₈O)²⁻. In 2, the seven-coordinated Ba²⁺ cations are connected to polymeric chains by L₁ ligands, and the metal atom is coordinated by five O atoms of three different L₁ ligands. The coordination polyhedron around the Ba²⁺ cation is a distorted monocapped trigonal prism. In 3, the two-dimensional framework is built up from one-dimensional chains containing two independent seven-coordinated Sr atoms connected by two crystallographically independent L₂ ligands, L₂ = (Cl₂CP₂O₅MeNC₄H₈)²⁻. The coordination polyhedron around the Sr²⁺ cations is a distorted monocapped trigonal prism. In 3 the chains are connected into a layered structure through the Sr(1) atoms, while in compounds 1 and 2 a layer-like construction is formed through hydrogen bonds.