{Zn6[MeN(CH2CO2)(CH2PO3)]6(Zn)}^4- Anion: The First Example of the Oxo-Bridged Zn6 Octahedron with a Centered Zn(II) Cation

Hydrothermal reactions of N-(phosphonomethyl)-N-methylglycine, MeN(CH2CO2H)(CH2PO3H2) (H3L), with zinc(II) acetate resulted in the formation of a novel zinc carboxylate-phosphonate, {Zn6L6(Zn)}{Zn(H2O)6}2·22H2O (1). The structure of 1 contains a heptanuclear zinc phosphonate cluster anion, {Zn6L6(Zn)}^4-, in which seven zinc(II) cations form an unusual Zn6(Zn) centered octahedron with six of its Zn3 triangle faces each further capped by a phosphonate group. The Zn(II) cations of the Zn6 octahedron are five-coordinated whereas the centered Zn(II) cation is octahedrally coordinated. Packing of these cluster anions creates micropores occupied by the hydrated zinc(II) cations as well as lattice water molecules. The structural skeleton of 1 is retained after the removal of the lattice water molecules.