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

Bis(di-2-pyridl sulfide)ruthenium(II) complexes containing the ligands Cl, NO2, NO, MeCN, py (pyridine), pyz (pyrazine) or 4,4'-bipyridine) have been prepared by usual methods and a new direct procedure from robust [Ru(dps)2Cl2] 1a (dps = di-2-pyridyl sulfide). This is the main of product of the reaction between dps and RuCl3 in refluxing dimethylformamide (dmf) while minor products are the complexes [Ru(dps)(dmf)(CO)Cl2] and [Ru(dps)2(CO)Cl][PF6]. The crystal structures of 1a has been determined: orthorhombic, space group Pbcn, a = 8.587(2), b = 16.421(3), c = 15.023(3) angstrom, Z = 4 and R = 0.024. The Ru atom exhibits an almost ideal octahedral co-ordination geometry involving two Cl 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)2Cl2][PF6]. The complexes have been characterized by infrared, UV/VIS, H-1 and C-13 NMR sprectroscopies. The H-1 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(pi)(Ru) --> pi* (dps) transition, is blue shifted with respect to that of [Ru(2,2'-bipy)2Cl2]. Further blue shifts are observed on replacing in the Cl-1a by stronger pi-acceptor ligands such as NO2-, MeCN and NO+.