Structures of Bisphosphonate Metal Complexes: Zinc and Cadmium Complexes of Clodronate and Its Partial Ester Derivatives

Four new zinc and cadmium bisphosphonates [{NaZn(Cl2CP2O6H)(H2O)5}]n (1), [{Cd2(Cl2CP2O6)(H2O)4}·H2O]n
(2), [{Zn(Cl2CP2O6Pri2)(H2O)3}·H2O]n (3), and [{Cd2(Cl2CP2O6Pri2)2(MeOH)2(H2O)2}·H2O]2 (4) have been prepared
and their crystal structures determined by single-crystal X-ray diffractometry. Two bisphosphonate ligands were
used:  clodronate, (dichloromethylene)bis(phosphonate) and its symmetrical P,P‘-diisopropyl ester derivative. The
structure of the Zn complex 1 is three-dimensional, consisting of one-dimensional Zn−clodronate chains connected
to the three-dimensional network by Na+ ions. The structure of Cd complex 2 consists of double layers, and a
unique bond was found between the Cd2+ cation and a Cl atom of clodronate. Zn complex 3 consists of one-dimensional chains, but the binding of the bisphosphonate ligands is unique:  in 3 the bisphosphonate ligand is
only bidentate. Compound 4 is a tetramer, and hydrogen bonds hold the tetramers together, forming a layered
structure.