Marina I. Naumova

The bivalent metal hypophosphites Sr(H2PO2)2, Pb(H2PO2)2 and Ba(H2PO2)2.

The structures of isomorphous monoclinic strontium and lead bis(dihydrogenphosphate), Sr(H2PO2)2 and Pb(H2PO2)2, and orthorhombic barium bis(dihydrogenphosphate), Ba(H2PO2)2, consist of layers of hypophosphite anions and metal cations exhibiting square antiprismatic coordination by O atoms. The Sr and Pb atoms are located on sites with point symmetry 2, and the Ba atoms are on sites with point symmetry 222. Within the layers, each anion bridges four metal cations.

Cadmium bis­[dihydrogenphosphate(I)]

# 2005 International Union of Crystallography Printed in Great Britain – all rights reserved The structure of monoclinic (C2/c) cadmium bis[dihydrogenphosphate(I)], [Cd(H2PO2)2], consists of layers located at x = 0 and 12. The Cd cation has a distorted octahedral coordination and dihydrogenphosphate(I) anions act as tridentate bridging ligands. The Cd atoms are on sites of twofold symmetry, while all other atoms are in general positions. The compound is isotypic with Ca(H2PO2)2 [Goedkoop & Loopstra (1959). Ned. Tijdschr. Natuurkd. 25, 29–41].

Hexaaquanickel(II) bis(hypophosphite)

The structure of hexaaquanickel(II) bis(hypophosphite), [Ni(H(2)O)(6)](H(2)PO(2))(2), has been determined. The crystals are prismatic. The packing of the Ni and P atoms (not the entire hypophosphite anions) is the same as in the structures of [Co(H(2)O)(6)](H(2)PO(2))(2) and [Co(0.5)Ni(0.5)(H(2)O)(6)](H(2)PO(2))(2). The Ni(II) cations have a pseudo-face-centered cubic cell, with cell parameter a approximately= 10.216 A and tetrahedral cavities occupied by P atoms. The Ni(II) cation has crystallographically imposed twofold symmetry and has an octahedral coordination sphere consisting of six water O atoms, two of which also lie on the twofold axis. The planes of oppositely coordinated water molecules are in a cross conformation. The geometry of the hypophosphite anion is close to point symmetry mm2. The hypophosphite anions are hydrogen bonded to the coordinated water molecules.

The alkali hypophosphites KH2PO2, RbH2PO2 and CsH2PO2

The structures of the hypophosphites KH(2)PO(2) (potassium hypophosphite), RbH(2)PO(2) (rubidium hypophosphite) and CsH(2)PO(2) (caesium hypophosphite) have been determined by single-crystal X-ray diffraction. The structures consist of layers of alkali cations and hypophosphite anions, with the latter bridging four cations within the same layer. The Rb and Cs hypophosphites are isomorphous.

Hexaaquacobalt(II) bis(hypophosphite) and hexaaquacobalt(II)/nickel(II) bis(hypophosphite).

The title compounds, hexaaquacobalt(II) bis(hypophosphite), [Co(H(2)O)(6)](H(2)PO(2))(2), and hexaaquacobalt(II)/nickel(II) bis(hypophosphite), [Co(0.5)Ni(0.5)(H(2)O)(6)](H(2)PO(2))(2), are shown to adopt the same structure as hexaaquamagnesium(II) bis(hypophosphite). The packing of the Co(Ni) and P atoms is the same as in the structure of CaF(2). The Co(II)(Ni(II)) atoms have a pseudo-face-centred cubic cell, with a = b approximately 10.3 A, and the P atoms occupy the tetrahedral cavities. The central metal cation has a slightly distorted octahedral coordination sphere. The geometry of the hypophosphite anion in the structure is very close to ideal, with point symmetry mm2. Each O atom of the hypophosphite anion is hydrogen bonded to three water molecules from different cation complexes, and each H atom of the hypophosphite anion is surrounded by three water molecules from further different cation complexes.