Hexaaquacobalt(II) bis[(2-Hydroxy-1,3-propanediamine-N,N,N',N'-tetraacetato)cobalt(III)]

The structure of the title complex, [Co(H2O)(6)][Co(C11H14N2O9)](2), is comprised of discrete [Co(hpdta)](-) anions (H(4)hpdta is 2-hydroxy-1,3-propanediamine-N,N,N',N'-tetraacetic acid) and [Co(H2O)(6)](2+) cations in a 2:1 molar ratio. The trivalent Co atom in the anion is coordinated by the hexadentate hpdta chelate ligand, with two amino-N atoms [Co--N 1,948(3) Angstrom] and four O atoms of the four monodentate carboxylato groups [Co--O 1.869(2)-1.914(2) Angstrom] in a distorted octahedral arrangement, whereas the divalent Co atom in the cation is coordinated in an octahedral manner by six aqua ligands [Co-O 2.078 (2)-2.124 (2) Angstrom]. The crystal structure is stabilized by extensive hydrogen bonding. Each aqua ligand forms two donor hydrogen bonds with the carboxyl O atoms from adjacent anions and the hydroxyl group forms a hydrogen bond with an adjacent carboxyl O atom.