~ Pergamon PII: S0277-5387(96)00500-- 1 Po!vhedron Vol. 16, No. 11, pp. 1793 1802, 1997 ~: 1997Elsevier ScienceLtd All rightsreserved.Printedin Great Britain 0277 5387/97 $17.00+0.00 Novel pentacoordinated ruthenium(ll) complexes with a NNS chelating ligand: synthesis, characterization and electrochemical studies Mosarraf Hossain, Shyamal Kumar Chattopadhyayt and Saktiprosad Ghosh* Department of Inorganic Chemistry, Indian Association for the Cultivation of Science, Calcutta 700 032, India. (Received 29 May 1996; accepted 14 October 1996) Abstract The NNS chelating donor N-2-mercaptophenyl-(2'-pyridyl)methylenimine (PabtH) reacted with Ru(PPh3)3C12 to give a series of ruthenium(II) complexes Ru(Pabt) (PPh3)X {X = CI(1), Br(3)}, Ru(Pabt) (PPh3)2C1 (2), [Ru(Pabt) (PPh3)L]CIO4 {L = l-Meimz (2a), 2-Meimz (le)}, [Ru(Pabt) (PPh3) (L')2]CIO4 {L'= l-Meimz (la), imz (lb), H20 (If)} and [Ru(Pabt) (PPh3) (L-L)]C104 {L-L = bpy (ld), Phen (le); bpy = 2, 2'-bipyridine, Phen = 1,10-phenanthroline}. They have been characterized using I R, UV-vis, {~H and 3tp} NMR, EPR, magnetic susceptibility at room temperature, measurement of molecular weight, molecular conductance in solution and elemental analysis. The stabilisation of the pentacoordinated 16-electron com- plexes (1, 3, le and 2a) is attributed to pg donation by the sulfur atom of the ligand Pabt. Square pyramidal structure is proposed for these pentacoordinated complexes. Electron transfer behaviour of all the complexes has been explored by cyclic voltammetry in CH2C12 and CH3CN using TEAP as the supporting electrolyte. The five-coordinated complexes display cathodically shifted oxidation waves in CH2C12, when TEAC1 was used as supporting electrolyte. Linear correlation of electrochemical data in terms of Lever's electrochemical parameter EL. and the energy of metal to ligand charge transfer band has been attempted. ~3 1997 Elsevier Science Ltd. All rights reserved. Keywords: pentacoordination; ruthenium(II) complexes; mixed ligand complexes; NNS-ligand; chemical reac- tivity; electrochemical studies. The chemistry of nitrogen-sulfur chelating ligands has witnessed phenomenal growth during the last decade. This was stimulated particularly by the discovery of the occurrence of similar donor environment in the prosthetic groups of several oxidoreductases [1,2]. However, one of the metal ions that has received little attention in such studies is ruthenium, probably because of its non-availability in biological systems. The relatively small amount of work so far carried out on ruthenium complexes involving such ligands indicate that they exhibit very interesting redox, elec- tronic and structural characteristics [3-9]. It is also *Author to whom all correspondence should be addressed. tPermanent address: Department of Chemistry, Bengal Engineering College (Deemed University), Howrah 711 103, West Bengal, India. well known that chelating nitrogen-sulfur donors can stabilise complexes of unusual oxidation states [10- 15] and uncommon coordination numbers of metal ions [13-16]. Such complexes are also known to par- ticipate in diverse redox reactions [17-19], sometimes even forming complete electrochemical series [17]. In this chemical milieu, the chemistry of ruthenium lig- ated to nitrogen-sulfur chelating ligands promises to be quite fascinating. This paper reports the synthesis and reactivity of ruthenium complexes of the NNS chelating ligand N-2-mercaptophenyl (2'-pyridyl) methylenimine (PabtH), which affords a few ruthenium complexes with unusual coordination number. Exploration of the redox behaviour of the ruthenium complexes of PabtH itself and those in which other coligands are present in the first coor- dination sphere of the ruthenium centre receives appropriate attention in this work. 1793