New Group 6 metal carbonyl derivatives of 2-(2?-pyridyl)benzimidazole: synthesis and spectroscopic studies Mostafa M.H. Khalil a , Hassan A.Mohamed b , Samir M. El-Medani b , Ramadan M.Ramadan a, * a Chemistry Department, Faculty of Science, Ain Shams University, Cairo, Egypt b Chemistry Department, Faculty of Science, Cairo University, El-Faiyum Branch, El-Faiyum, Egypt Received 20 June 2002; received in revised form 5 September 2002; accepted 13 September 2002 Abstract Reaction of Cr(CO) 6 with 2-(2?-pyridyl)benzimidazole (pbiH) under reduced pressure resulted in the formation o dinuclear complex [Cr 2 (CO) 6 (pbiH) 2 ]. Infra-red (IR) spectroscopy revealed the presence of terminal and bridge Cr /CO bonds.Interaction ofM(CO) 6 ,M /Cr, Mo and W, with pbiH in the presence of 2,2?-bipyridine (bpy) gave the tetracarbonyl complexes [M(CO) 4 (pbiH)] × /bpy. Spectroscopic studies of the complexes indicated the presence of hydrogen bonding between the bpy nitrogen and the NH group of pbiH. Reactions ofM(CO) 6 with pbiH in the presence of PPh 3 gave the tricarbonyl monosubstituted derivatives [M(CO) 3 (PPh 3 )(pbiH)]. The spectroscopic studies of the complexes suggested the proposed structures. # 2002 Elsevier Science B.V. All rights reserved. Keywords: Metal carbonyls; Benzimidazole complexes; PPh 3 complexes; Spectra; Charge transfer; Hydrogen bonding; Proton transfer 1. Introduction Interest in transition metal complexes of imida- zoles and benzimidazoles stems from their abilities of proton, metal-to-ligandor ligand-to-metal chargetransfers [1 /4]. For example,iron and ruthenium complexesof the type [M /LH] n (whereM /[Ru(NH 3 ) 5 ] 2,3 or [Fe(CN) 5 ] 3,2 and LH /benzotriazoleor benzimidazole) were characterizedby electrochemical and spectro electro-chemical methods.The E 1/2 versuspH curveswere used to illustratethe relationship between theredox and acid /basespecies,and their interconversion equilibrium. The dependence of the M III /M II couple on the pH was taken into account in order to evaluate the usefulness of such simple complexes as modelsfor proton-coupled electron transfer. The results were interpreted in terms of the acceptor/donor electronic character of the ligands and s, p-metal /ligand interactions in both redox states of the metal ion [5]. On the other * Corresponding author. Tel.: /20-966-7-2294069. E-mail address: r_m_ramadan@yahoo.com (R.M. Ramadan). Spectrochimica Acta Part A 59 (2003) 1341 / 1347 www.elsevier.com/locate/saa 1386-1425/02/$ - see front matter # 2002 Elsevier Science B.V. All rights reserved. PII: S 1 3 8 6 - 1 4 2 5 ( 0 2 ) 0 0 3 3 0 - X