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

摘要

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.