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 Xray diffractometry. Previously, a monomeric structure, [Ca{Cl2C(PO3H)(2)}(H2O)(5)] (1), has been determined, but the new structures are polymeric: [{Ca-2[Cl2C(PO3)(2)](H2O)(6)}(.) 4.5H(2)O](n) (2), [{Ca2Na0.5[Cl2C(PO3)(2)](H2O)(8)}Cl(0.5)(.)4H(2)O](n) (3) and [{Ca-5[Cl2C(PO3)(2)](2)(H2O)(15)}(NO3)(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 tri-clinic crystal system, the space group being Pi with Z = 2. Compound 2 consists of Ca atoms and Cl2MBP 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 Cl2MBP- 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. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004).