Dinuclear Pd(II) complexes with the anionic form of 4,5-dihydro-1,2,4-triazolo[1,5-a]pyrimidine-5-one

This article describes the synthesis, spectroscopic characterization and single crystal X-ray structure of several Pd(II) dinuclear complexes with the ligand 4,5-dihydro-1,2,4-triazolo[1,5-a]pyrimidine-5-one (5HtpO) in its anionic form (5tpO(-)). The synthesis and characterization of the related mononuclear compound [PdCl2(5HtPO)(2)] is also included. This compound is transformed into the dinuclear [Pd-2(5tPO)(4)] (.) 4H(2)O by raising the pH, the structure of which indicates a head-tail-head-tail disposition of the heterocycles (D-2d symmetry) as a difference with the analogous Cu(II) and Pt(II) clusters. Using the auxiliary ligands bipyridine (bpy), phenanthroline (phen) and traiis-1,2-diaminocyclohexane (t-dach, racemic mixture), dinuclear compounds with the general formula [Pd-2(5tPO)2(a-a)(2)](NO3)(2) (.) nH(2)O are obtained. The crystal structure of those with a-a = phen and a-a = t-dach have been solved showing a head-tail disposition of the organic ligands, in contrast with the NMR data for a-a = bpy, which point to a head-head disposition. (C) 2004 Elsevier Ltd. All rights reserved.