Chemistry of azopyrimidines. Part II. Synthesis, spectra, electrochemistry and X-ray crystal structures of isomeric dichloro bis[2-(arylazo)pyrimidine] complexes of ruthenium(II)

2-(Arylazo)pyrimidines (aapm, 3) are new N,N'-chelating ligands in the azoimine family and were reacted with RuCl3 in ethanol under refluxing conditions. Three isomers of the composition Ru(aapm)(2)Cl-2 have been chromatographically separated and are established as having trans-cis-cis (tcc), cis-trans-cis (ctc) and cis-cis-cis (ccc) configurations with reference to the order of coordination pairs as Cl; N(pyrimidine), N and N(azo), N'. Two of the three isomeric structures have been confirmed by X-ray crystallography. In both of these structures, the Ru-N(azo) distances are relatively shorter than those of Ru-N(pyrimidine), indicating stronger bonding in the former and the presence of a Ru-(aapm) pi-interaction that is localised in the Ru-azo fragment. The isomer configuration is supported by IR and H-1 NMR data. The complexes exhibit t(2)(Ru)-->pi*(aapm) MLCT transitions in the visible region. Redox studies show the Ru(III)/Ru(II) couple in the green complexes [tcc-Ru(aapm)(2)Cl-2] at 1.1-1.2 V and in the blue complexes [ctc- and ccc-Ru(aapm)(2)Cl-2] at 1.2-1.4 V versus saturated calomel electrode (SCE) and two successive azo reductions. The difference in the first metal and ligand redox potentials is linearly correlated with nu(CT) [t(2)(Ru)-->pi*(aapm)]. (C) 1999 Elsevier Science Ltd. All rights reserved.