Organoammonium diphosphopentamolybdates(VI): influence of organic cations and anion protonation on crystal packing and geometrical features of polyanion

Abstract

Four organoammonium diphosphopentamolybdate(VI) with the formulae (C 5H 7N 2) 6[P 2Mo 5O 23]·5H 2O ( 1), (C 2H 10N 2) 3[P 2Mo 5O 23]·6H 2O ( 2), Al(C 4H 15N 3) 4[HP 2Mo 5O 23] 2Cl·10H 2O ( 3) and (C 4H 12N) 4[H 2P 2Mo 5O 23]·5H 2O ( 4) have been synthesized. The crystal structures have been determined by means of single crystal X-ray diffraction data. The geometrical characteristics of the [H n P 2Mo 5O 23] (6− n)− heteropolyanions have been compared with those described in the literature for other salts. Several relationships between the protonated state and topological changes in the heteropolyanions have been found. The crystal structure in compound 1 is stabilized by electrostatic forces, an extensive network of hydrogen contacts involving anions, cations and water molecules and π–π interactions among 4-aminopyridinium cations. The anions of compound 2 are arranged in layers perpendicular to the [ 1 ̄ 10] direction. The interactions between anions are established through hydrogen contacts which involve water molecules and ethylenediammonium cations. The monohydrogendiphosphopentamolybdate(VI) anions in the crystal structure of compound 3 are joined along the [010] direction by means of strong O–H⋯O interactions ( d(O⋯O)=2.529(10) Å) which lead to a polymeric structure of [HP 2Mo 5O 23] 5− polyanions. Likewise, a similar anion polymeric arrangement is found in compound 4 in which the diprotonated polyanions are held together by means of two strong hydrogen bonds ( d(O⋯O)=2.591(6) and 2.596(6) Å).