Synthesis, Characterization and Crystal Structure of Calcium-3-amino-1-hydroxypropylidene-1,1-bisphosphonic Acid

Abstract

Following the strategy of using polyfunctional phosphonic acids for the synthesis of open-framework metal phosphonates, 3-amino-1-hydroxypropylidene-1,1-bisphosphonic acid was used in the synthesis of a new calcium phosphonate. The compound, calcium-3-amino-1-hydroxypropylidene- 1,1-bisphosphonic acid [Ca_0.5{(H₃N⁺CH₂CH₂)C(OH)-(PO₃H–)(PO₂H–)}₂].H₂O (1) is a three-dimensional framework prepared by nonhydrothermal synthesis route. The asymmetric unit contains one independent Ca atoms, two chelating and bridging phosphonic ligands and one lattice water molecule. The structure of 1 is built up from CaO₆ polyhedra forming CaO chains connected to a three-dimensional metal-oxygen-metal framework with ammonium propyl groups pointing into the space between these layers. There are empty pore within the layers along the ‘c’ direction.