Trigonal bipyramidal penta-aquazinc(II): crystal structure of penta-aquazinc(II) bis(3,3′,3″-phosphinetriyltripropionato)dizincate(II,II) heptahydrate

Abstract

Crystals of the title compound are hexagonal, space group P6₁ or P6₅. The crystal structure was determined by the heavy-atom method from 2 675 unique reflections and refined to R= 0.059. The structure can be best formulated as an ionic polymer with the composition ([Zn(H₂O)₅][Zn₂{P(CH₂CH₂CO₂)₃}₂]·7H₂O)_n. It consists of a three-dimensional network of [Zn{P(CH₂CH₂CO₂)₃}]^– anions, where the zinc atoms are each tetrahedrally co-ordinated by three carboxyl oxygen atoms belonging to three different 3,3′,3″-phosphinetriyltripropionato ligands [Zn–O, 1.950(12)–1.991 (13)Å] and by one phosphorus atom from a fourth ligand [Zn–P, 2.405(4) and 2.429(4)Å; the first crystallographically documented zinc–phosphine bond]. Zinc cations are located in holes of the network as the hitherto unknown [Zn(H₂O)₅]²⁺ moieties with trigonal bipyramidal arrangement. The structure is stabilized by hydrogen bonding in which carboxylate oxygen atoms and both coordinated and lattice water molecules are involved.