Ligand-induced electronic effects in the physical properties of transition metal clusters: Modulation of Mössbauer parameters and magnetic exchange couplings in complexes image by the R substituent

The syntheses, crystallographic, 57Fe Mössbauer and magnetic studies of the diferric complexes [Fe2O(O2CR)2(phen)2(H2O)2](ClO4)2 [R = H (3), CH2F (4)] are reported and the results are compared to those of the previously reported analogues with R = CCl3 (1) and R = CMe3 (2) [Boudalis et al., Polyhedron 25 (2006) 1391]. The Mössbauer spectra of 3 and 4 consist of symmetric quadrupole-split doublets [δ = 0.392(1) mm s−1, ΔE Q = 1.726 mm s−1 (3) and δ = 0.398 mm s−1, ΔE Q = 1.691 mm s−1 (4), at 78 K]. The magnetic couplings within 2–4 are antiferromagnetic [J = −140 (2), −129 (3) and −116 (4) cm−1, View the MathML sourceHˆ=-2JSˆ1·Sˆ2]. The results from Mössbauer spectroscopic and variable-temperature magnetic studies are discussed in terms of structural characteristics of the complexes and the electron donating strengths of the carboxylate R substituents. In addition, the syntheses and structures of complexes [Fe3O(O2CR)6(H2O)3](ClO4) [R = H (5), CH2F (6)], which were derived as by-products from the syntheses of 3 and 4, are described.