Synthesis and spectroscopic properties of di-2-pyridyl sulfide (dps) compounds. Crystal structure of [Ru(dps)2Cl2]

Abstract

Bis(di-2-pyridyl sulfide)ruthenium(II) complexes containing the ligands CI, NO₂, NO, MeCN, py (pyridine), pyz (pyrazine) or 4,4′-bipy (4,4′-bipyridine) have been prepared by usual methods and a new direct procedure from robust [Ru(dps)₂CI₂]1a(dps = di-2-pyridyl sulfide). This is the main product of the reaction between dps and RuCl₃ in refluxing dimethylformamide (dmf) while minor products are the complexes [Ru(dps)(dmf)(CO)CI₂] and [Ru(dps)₂(CO)CI][PF₆]. The crystal structure of 1a has been determined: orthorhombic, space group Pbcn, a= 8.587(2), b= 16.421(3), c= 15.023(3)Å, Z= 4 and R= 0.024. The Ru atom exhibits an almost ideal octahedral co-ordination geometry involving two CI atoms, in cis position, and the two dps ligands chelated through the respective pyridine N atoms. Each dps adopts a twisted N,N-inside conformation. The six-membered chelate rings show boat conformations with the Ru and S atoms out of the plane through the other four atoms on the same side. Oxidation of 1a by HNO₃ or cerium(IV) salts, followed by precipitation with NH₄PF₆, gave [Ru(dps)₂CI₂][PF₆]. The complexes have been characterized by infrared, UV/VIS, ¹H and ¹³C NMR spectroscopies. The ¹H NMR resonances of the pyz and 4,4′-bipy derivatives were assigned by employment of correlation spectra. The lowest-energy band in the visible spectrum of 1a, assigned as a d_π(Ru)→π*(dps) transition, is blue shifted with respect to that of [Ru(2,2′-bipy)₂CI₂]. Further blue shifts are observed on replacing in the Cl^–1a by stronger π-acceptor ligands such as NO₂^–, MeCN and NO⁺.