Pt(II) and Pt(IV) chloride complexes with 1,2,4-triazolo-[1,5alpha]-pyrimidines: trans[Pt(tp)(2)Cl-2], trans-[Pt(dmtp)(2)Cl-2], trans[Pt(tp)(2)Cl-4] and trans-[Pt(dmtp)(2)Cl-4] where tp = 1,2,4-triazolo-[1,5alpha]-pyrimidine and dmtp = 5,7-dimethyl-1,2,4-triazolo-[1,5a]pyrimidine were synthesised and studied by H-1, C-13, N-15, Pt-195 NMR and IR spectroscopies. Significant N-15 NMR upfield coordination shifts (92-96 ppm) were observed for the N(3) atom indicating that this nitrogen is the metallation site. The X-ray structure of an ionic pair (dmtpH)(2)[PtCl6] {bis(5,7-dimethyl-1,2,4-triazolo-[1,5alpha]-pyrimidinium) hexachloroplatinate(IV)} was determined. exhibiting the presence of unique (dmtpH)(2)(2+) dimeric cations, protonated at N(3), N(3') atoms and linked by hydrogen bonding. (C) 2002 Elsevier Science Ltd. All rights reserved.