title: Hexaaquacobalt(II) bis[hydrogen bis(4-carboxyphenylphosphonate)] dihydrate.
abstract: The Co(II) ion in the title complex salt, [Co(H(2)O)(6)](C(14)H(13)O(10)P(2))(2)·2H(2)O or [Co(H(2)O)(6)][H(C(7)H(6)O(5)P)(2)]·2H(2)O, resides on an inversion centre and exhibits an octahedral environment formed by six aqua ligands. Two unique acid residues share an H atom between their phosphonate groups, forming a complex monoanion with a very short (P)O···H···O(P) hydrogen bond of 2.435 (2) Å. The crystal structure is layered and consists of thick organic bilayers with hydrated metal [Co(H(2)O)(6)](2+) ions arranged between them. The interior of the bilayer is occupied by the aromatic portions of the complex monoanions and the carboxyl groups, which form hydrogen-bonded R(2)(2)(8) ring motifs. The phosphonate groups are arranged outwards in order to form the hydrogen-bonded surfaces of the bilayer. Electrostatic and multiple hydrogen-bond interactions, established between the coordination and solvent water molecules and the phosphonate O atoms, hold neighbouring bilayers together.
authors.affiliation: Department of Chemistry, Wrocław University of Technology, 27 Wybrzeże Wyspiańskiego Street, 50-370 Wrocław, Poland.
authors.forename: Magdalena
authors.initials: M
authors.lastname: Wilk
authors.forename: Jan
authors.initials: J
authors.lastname: Janczak
authors.forename: Veneta
authors.initials: V
authors.lastname: Videnova-Adrabinska