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

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 s pecies 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 2(NH3)(2)(1-MeC(-)-N3,N 4)(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) Angs trom, 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 methylcytosin ato 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 diastereomeri c forms, however, as evident from 1(H) NMR spectroscopy. On the basis of 5, an oligomerization process leading to ''Pt cytosine blue'' is pr oposed, according to which O(2) of 1-MeC(-) is involved in bridging di nuclear entities or dinuclear and mononuclear entities. The proposed o ligomerization principle differs markedly from that observed in tetran uclear (Pt-2.25+)(4) complexes containing cyclic amidate ligands.