The first bifunctional Gd(III) complexes covalently bound to arylphosphonium cations and the first tumour-cell selective mitochondrial agents designed for potential application in binary cancer therapies are reported. The highest in vitro cellular uptake for any Gd complex reported to date is described, with levels exceeding 10(10) Gd atoms per tumour cell.

The first examples of arylphosphonium salts containing a dicarba-closo-dodecaborane(12) (closo-carborane) are reported; in contrast to the 1,12-carborane derivative, the 1,2- and 1,7-isomers undergo a facile deboronation reaction in polar solvents to afford the corresponding nido-carborane phosphonium zwitterions.

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[1,2-Bis(diphenylphosphino)-1,2-dicarbacloso-dodecaborane-j Key indicators: single-crystal X-ray study; T = 150 K; mean (C-C) = 0.010 Å; Hatom completeness 99%; disorder in main residue; R factor = 0.044; wR factor = 0.094; data-to-parameter ratio = 14.8.The title compound, [Au(C 26 H 30 B 10 P 2 )(C 26 H 30 B 9 P 2 )]Á-0.5CH 2 Cl 2 Á0.5H 2 O, contains two independent complex molecules in the asymmetric unit. The gold(I) centres display a distorted tetrahedral geometry. The complex is stablized through weak intramolecular -stacking (CgÁ Á ÁCg = 4.17 Å ) and edge-to-face interactions (HÁ Á ÁCg = 3.21 Å ). Adjacent molecules interact through C-HÁ Á Á (HÁ Á ÁCg = 2.88 Å ) and B-HÁ Á Á (HÁ Á ÁCg = 3.15 Å ) contacts, forming a threedimensional network, with solvent molecules occupying the cavities. One of the phenyl groups was disordered over two sites with occupancy factors of 0.65 and 0.35. Related literatureThe chelating P-donor ligand 1,2-bis(diphenylphosphino)-1,2-dicarba-closo-carborane has been used to prepare 2-, 3-and 4-coordinate complexes of gold(I) (Crespo et al., 1992(Crespo et al., , 1994 AlBaker et al., 1985). Coordination of this ligand has often led to deboronation of the closo-carborane cage to afford the corresponding nido-carborane in polar solvents (Teixidor et al., 1995(Teixidor et al., , 1996. A non-solvated crystal structure of the title compound has been reported previously (Crespo et al., 1997). Facile deboronation of the carborane cage in polar solvents has also been observed when substituents to the cage are electron withdrawing (Shaeck & Kahl, 1999; Ioppolo et al., 2007a,b). In contrast, our group has shown that ligands containing the thermodynamically stable 1,12-carborane cluster do not degrade upon complexation to gold(I) (Ioppolo et al., 2007a,b