Crystal structure and Moessbauer spectroscopic studies of oxo-centered trinuclear chloroacetate complexes

The crystal structures of oxo-centered trinuclear cobalt-iron chloroacetate complex [CoIIFe2III(CH2ClCO2)6(H2O)3] x 3H2O (1) was compared with that of previously reported trinuclear iron complex [FeIIFe2IIIO(CH2ClCO2)6(H2O)3] x 3H2O (2) which has an isomorphous structure to 1. Compound 1 crystallizes in space group P21/n with Z = 4 in a unit cell of a = 14.826 (4) A radical, b = 4.536 (8) A radical, c = 14.000 (4) A radical, Β = 100.32 (2) and V = 2968 (11) A radical3. The structure was refined to R = 0.75 and Rw = 0.82. The coordination geometries of the three iron atoms are observed equivalent in 1 indicating a static disorder of the position among cobalt and iron atoms. Two distinct FeIII doublets observed in Moessbauer spectra of 1 become an indistinguishable broad doublet by dehydration of crystal water. On the other hand, no significant line-broadening is observed after thee dehydration in complex 2. The results indicate that the dehydration in 2 induced a local environmental change reordering of an electronic configuration around iron atoms, whereas the remaining disordering is reflected in Moessbauer spectrum after the dehydration in 1. (author) 2 refs.; 3 figs.; 2 tabs