Metal-purine interactions: Homo- and heterodinuclear platinum(II) and/or palladium(II) complexes of 8-thiotheophylline. Crystal structures of [Pt(mu-TT)(dppm)](2)center dot 2DMSO and [(dppm)Pt(mu-TT)(2)Pd(dppm)]center dot 7H(2)O

The reaction of cis-[MCl(2)(dppm)] (M = Pt(II) and Pd(II); dppm = bis(diphenylphosphino)methane) with H2TT and NaOH (H2TT = 8-thiotheophylline) yields neutral mononuclear [M(HTT-S(8))(2)(dppm)] complexes. Homodinuclear [M(mu-TT-N(7),S(8))(dppm)](2) (M = Pt(II) and Pd(II) are prepared either by the reaction of [M(HTT)(2)(dppm)] with cis-[MCl(2)(dppm)] and NaOH or by the direct reaction of cis-[MCl(2)(dppm)] with Na2TT, prepared in situ from H2TT and NaOH. The crystal structure of the Pt derivative is reported: [Pt(mu-TT)(dppm)](2) . 2DMSO (3) crystallizes in the triclinic space group <P(1)over bar> with a = 12.939(3) Angstrom, b = 13.009(3) Angstrom, c = 22.980(5) Angstrom, alpha = 96.89(3)degrees, beta = 103.53(3)degrees, gamma = 106.43(3)degrees, Z = 2, and R(1) = 0.045. Heterodinuclear [(dppm)Pt(mu-TT)(2)Pd(L-L)] complexes are obtained by reaction of [Pt(HTT)(2)(dppm)] with [PdCl2(L-L)] in basic medium (L-L = dppm and 2,2'-bipyridine). The crystal structure of [(dppm)Pt(mu-TT)(2)Pd(dppm)]. 7H(2)O (5) is reported. The complex crystallizes in the orthorhombic space group P2(1)2(1)2(1) With a = 16.560(5) Angstrom, b = 17.063(5) Angstrom, c = 24.428(5) Angstrom, Z = 4, and R(1) = 0.042. The structures of 3 and 5 are almost identical, by which 5 can be seen as an isomorphic substitution of one of the Pt(II) ions of 3 by a Pd(II) ion. The structures consist of dinuclear units having a pseudo-2-fold axis perpendicular to that defined by the metal atoms. The two metal atoms are bibridged by two mu-TT-N(7),S(8) ligands, in a head to tail arrangement. The square-planar coordination of the metal atoms is completed by a chelate dppm ligand. The steric repulsions between the bulky dppm ligands must be the main factor precluding metal-metal interaction in these compounds.