A Structural Study of Bisphosphonate Metal Complexes − Three New Polymeric Structures of the Calcium Complex of Clodronic Acid

Abstract

Abstract Three novel calcium complexes of clodronic acid were prepared and their structures determined by single‐crystal X‐ray diffractometry. Previously, a monomeric structure, [Ca{Cl 2 C(PO 3 H) 2 }(H 2 O) 5 ] ( 1 ), has been determined, but the new structures are polymeric: [{Ca 2 [Cl 2 C(PO 3 ) 2 ](H 2 O) 6 }·4.5H 2 O] n ( 2 ), [{Ca 2 Na 0.5 [Cl 2 C(PO 3 ) 2 ](H 2 O) 8 }Cl 0.5 ·4H 2 O] n ( 3 ) and [{Ca 5 [Cl 2 C(PO 3 ) 2 ] 2 (H 2 O) 15 }(NO 3 ) 2 ·1.5H 2 O] n ( 4 ); and they provide new, important information about the binding abilities of clodronic acid. Compounds 2−4 crystallise in the triclinic crystal system, the space group being P $\bar 1$ with Z = 2. Compound 2 consists of Ca atoms and Cl 2 MBP ligands connected to one‐dimensional chains. The chains are held together by hydrogen bonds formed by aqua ligands and lattice water molecules. The structure of 3 consists of similar calcium clodronate chains forming two‐dimensional layers through additional, six‐coordinate Na atoms. Compound 4 consists of two‐dimensional calcium clodronate layers, the calcium atoms are connected by Cl 2 MBP− and aqua ligands. The nitrate groups and lattice water molecules lie between the layers and hold them together. The layered compounds 3 and 4 reveal substantial porosity. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)