DIMERIZATION OF TRANS-[PT(NH3)(1-MEC-N3)(H2O)(2)](2+) AND OXIDATION TO A DIPLATINUM(III) SPECIES IN THE PRESENCE OF GLYCINE - RELEVANCE FOR PLATINUM CYTOSINE BLUE

trans-Pt(NH3)(1-MeC-N3)I-2 (4) with 1-MeC (1-methylcytosine) bound to Pt via N(3), obtained from cis-[Pt(NH3)(2)(1-MeC-N3)Cl]Cl, gives trans-[Pt(NH3)(1-MeC-N3) (H2O)(2)](2+) when treated with 2 equiv of AgNO3. This diaqua species rapidly dimerizes in solution to give [Pt-2(NH3)(2)(1-MeC(-)-N3,N4)(2)(H2O)(2)](2+) (5), a compound containing bridging 1-methylcytosinato ligands in a head-tail arrangement, as judged from H-1 NMR spectroscopy. In addition, an intensely purple, paramagnetic species 5' forms, which is yet another representative of the class of ''platinum pyrimidine blues''. If dimerization to give 5 is carried out in the presence of the amino acid glycine, spontaneous oxidation to a yellow diplatinum(III) complex of composition [Pt-2(NH3)(2)(1-MeC(-)-N3,N4)(2)(gly-N,O)(2)]-(NO3)(2) . 3H(2)O (6) takes place. The compound has been isolated and characterized bp NMR spectroscopy (H-1, Pt-195) and X-ray crystallography: triclinic system, space group P $$($) over bar 1, a = 12.438(4) Angstrom, b = 12.820(4) Angstrom, c = 10.275(2) Angstrom, alpha = 98.21(3)degrees, beta = 112.84(2)degrees, gamma = 62.24(2)degrees, V = 1335(2) Angstrom(3), Z = 2. In 6, the two methylcytosinato rings are okenled head-tail, and glycinate anions chelate Pt atoms via NH2 (axial) and COO- (equatorial). The Pt-Pt bond length is 2.527(1) Angstrom. When L-alanine is applied instead of glycine, a complex analogous to 6 is formed which occurs in solution in two diastereomeric forms, however, as evident from 1(H) NMR spectroscopy. On the basis of 5, an oligomerization process leading to ''Pt cytosine blue'' is proposed, according to which O(2) of 1-MeC(-) is involved in bridging dinuclear entities or dinuclear and mononuclear entities. The proposed oligomerization principle differs markedly from that observed in tetranuclear (Pt-2.25+)(4) complexes containing cyclic amidate ligands.