Platinum complexes with the novel ligand diethyl [(methylsulfinyl)methyl]phosphonate (SMP): Solid-state characterization of potassium trichloro(SMP)platinum(II) which, in solution, gives dichloro(SMP)-platinum(II) and potassium chloride

Phosphonate ligands have been employed in the synthesis of platinum complexes, which are active against bone tumors. The stability of a new compound of this family, [PtCl2(SMP)] {1; SMP = diethyl[(methylsulfinyl)methyl]phosphonate), has been investigated in water and acetone. The compound is stable in aqueous solution where it undergoes only partial solvolysis that is completely repressed by addition of free chloride ions. However, crystallization of 1 from water/acetone/chloroform (0.2:1:1, v/v/v) containing an equimolar amount of KCl affords a new compound containing monodentate SMP {K[PtCl3(SMP-S], 2}. Dissolution of 2 in water or acetone restores 1. The driving force in the formation of 2 appears to be the network of electrostatic interactions between cations and complex anions in the solid state. It is not only the detached P=O oxygen atom, but also the oxygen atom bound to the sulfur atom and a coordinated chloride ligand of the same platinum unit that interact rather strongly with the cation. It is expected that the same reaction (partial detachment of the phosphonate and anchoring of the cation) can take place in hypercalcaemic districts associated to bone tumors. (c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005).