SPECTROCHIMICA ACTA PART A ELSEVIER Spectrochimica Acta Part A 52 (1996) 1815-1821 M6ssbauer, vibrational and electronic spectroscopy of trinuclear la-oxo iron(III) acetate clusters with pyridine and derivatives as ligands Christiane Fernandes a, Eduardo Stadler a'*, Valderes Drago b, Carlos Jorge da Cunha c, Izaura Hiroko Kuwabara c ~Departamento de Quimica, Universidade Federal de Santa Catarina, Caixa Postal 476, 88.040-970, Floriandpolis, Santa Catarina, Brazil bDepartamento de Fisica, Universidade Federal de Santa Catarina, Caixa Postal 476, 88040-970, Floriandpolis, Santa Catarina, Brazil ~Departamento de Quimica, Universidade Federal do Parangt, 81.531-970, Curitiba, Parangt, Brazil Received 1 November 1995; accepted 5 June 1996 Abstract In this study we have investigated eight complexes of the general composition [Fe30(OOCCH3)6(L)3]NO3, where L is a heterocyclic ligand, viz. a 4-substituted pyridine. The M6ssbauer spectra of the complexes showed isomer shifts and quadrupole splittings that are characteristic of iron(III) high-spin complexes. The M6ssbauer quadrupolar doublets showed asymmetries that are attributed principally to the Goldanskii-Karyagin effect. A correlation is proposed between the M6ssbauer parameters, and between the energy of the charge transfer band spectra, and the pKa values of the N-heterocyclic ligands. Keywords: M6ssbauer and Infrared spectra; Trinuclear p-oxo iron(III); Pyridine; Derivatives; Acetate clusters I. Introduction The chemistry of transition metal carboxylates has been arousing the interest of researchers since the end of the last century, when the first com- plexes were obtained. For a number of years, research in this area did not go beyond the eluci- dation of the structures, which was achieved only in 1965, when Figgis and Robertson [1] deter- * Corresponding author. mined the structure of chromium(III) carboxylate by crystal X-ray diffraction. Besides chromium, other metals show the same kind of structure, e.g. V, Mn, Fe, Co, Rh, Ir, Ru, W, Mo and Pd, with the general formula [M30(OOCR)6L~ ] +, where M is the metal and R is CH 3 [2,3]. In this cluster family, the carboxylates of iron are quite well known because they are easily obtained. They show a trigonal structure with two acetate bridges joining each pair of metal ions, and also a g-oxo central bridge, in a flat triangu- 0584-8539/96/$15.00 Copyright © 1996 Elsevier Science B.V. All rights reserved PH S0584-8539(96)01753-9