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

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)