X-Ray Structure and In Vitro Anti-Tumoural Activity of the Dimeric Bis[(2-Phenyl-1,2-Dicarba-Closo-Dodecaborane-1-Carboxylato)-Di-n-Butyltin] Oxide

X-ray diffraction studies reveal the structure of {[(2-C(6)H(5)-1,2-C(2)B(10)H(10)-1-COO)Bu(2)Sn](2)O}(2), 1, to conform to the common motif found for {[(R'COO)R(2)Sn](2)O}(2) compounds. The dimer features a central Bu(2)Sn(2)O(2) unit (two-fold symmetry) with the two Bu(2)Sn groups being linked via bridging oxygen atoms, each of which also carries an exocyclic Bu(2)Sn moiety. The two pairs of exo- and endo-cyclic tin atoms are each linked via an almost symmetrically bridging carboxylate ligand and the two remaining ligands coordinate an exocyclic tin atom only, in the monodentate mode. The in vitro anti-tumour activity of 1, determined against a variety of cell lines, is compared with those of the corresponding 2-methylcarboranylacetate, derivative 2, and with clinically used compounds.