Iron, copper and zinc ammonium-1-hydroxyalkylidene-diphosphonates with zero-, one- and two-dimensional covalent metal–ligand structures extended into three-dimensional supramolecular networks by charge-assisted hydrogen-bonding

Abstract

Hydrothermal synthesis with MCl 2 (M = Fe, Cu, and Zn) and disodium 5-ammonium-1-hydroxypentylidene-1,1-bisphosphonate, (Na +) 2[ +H 3N(CH 2) 4C(OH)(PO 3 2−)(PO 3H −)] (Na 2HAC 5OHP 2) or sodium 3-ammonium-1-hydroxypropylidene-1,1-bisphosphonate hydrate, Na +[ +H 3N(CH 2) 2C(OH)(PO 3H –)(PO 3H –)]·H 2O (NaH 2PAM·H 2O) the sodium salt of pamidronic acid, H 3PAM) yielded the one-dimensional (1D) iron, molecular copper and two-dimensional (2D) zinc compounds 1D-{[Fe(μ 3-η 5-HAC 5OHP 2)]·H 2O}, 1, [Cu(η 2-H 2AC 5OHP 2) 2], 2, 2D-{[Zn 2(μ 5-η 7-AC 5OHP 2)Cl], 3, and 2D-{[Zn(μ 2-η 3-H 2PAM) 2], 4, respectively. The bisphosphonate ligand bridges (μ n ) between 2– 5 metal atoms and uses 2– 7 oxygen donor atoms towards metal coordination (η n ). The zwitterionic nature of the now bis- or tetrakis-deprotonated ammonium–bisphosphonate is retained in the metal complexes. From the reaction of NiCl 2 and Na 2HAC 5OHP 2 the zwitterionic 5-ammonium-1-hydroxypentylidene-1-phosphonic acid, +H 3N(CH 2) 4CH(OH)PO 3H −, 5 was obtained as a product of the ligand P–C bond hydrolysis. Adjacent strands, molecules or layers in 1– 4, respectively are organized through the Coulomb attraction between the positive ammonium group and the negative phosphonate groups, supported by hydrogen-bonding. Each protic H atom on the C–OH, NH 3 + and –PO 3H − group is involved in charge-assisted hydrogen-bonding. The ammonium-pentylidene groups act as hydrophobic separators between the hydrophilic units with the polar M{C(OH)(PO 3) 2} and {NH 3} units. Bond valence sum calculations support the Fe(II) oxidation state in 1, which was experimentally determined from a quantitative polarographic Fe(II)/Fe(III) speciation analysis as well as a temperature variable magnetic study.