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

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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 dπ(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+.