Isomorphous phosphonoacetic acid salts with magnesium(II), manganese(II), cobalt(II), zinc(II) and copper(II)

Abstract

Abstract All crystals of the title compounds, with general formula M2+(C2H4O5P–)2(H2O)2, (MAP), are isomorphous and crystallize in the space group P1̅ with Z = 2. The two crystallographically independent M2+ cations are situated on a center of symmetry and are octahedrally coordinated by two phosphonate monoanions and two water molecules. In the case of Cu2+ cation, Jahn-Teller effect causes strong extension of two Cu—O bonds. The mono anions coordinate the metal ions by one carboxylic and one phosphonate oxygen atom, which is facilitated by their specific overall conformation. In each monoanion, one of the phosphonate O atoms is nearly antiperiplanar ap to the carboxylic C atom, and the remaining phosphonate O atoms are nearly gauche (+sc and –sc) with respect to the mentioned C atom. The carboxylic O atoms are in positions close to +sc and –ac in relation to the phosphonate P atom. The complex molecules form well separated layers in all MAP compounds. The phosphonate and carboxylic groups act as donors in medium strong and weak intermolecular O—H...O hydrogen bonding and, as acceptors, in C—H...O hydrogen interactions in all structures. Additionally both crystallographically independent water molecules are donors of weak hydrogen bonding to phosphonate oxygen atoms from adjacent complex molecules.