ANTIFERROMAGNETIC EXCHANGE IN AN ISOMORPHOUS SERIES OF SILOXY-BRIDGED EARLY-TRANSITION-METAL DIMERS - COMPARISONS OF ANTIFERROMAGNETIC EXCHANGE INTERACTIONS IN ISOMORPHOUS D1-D1, D1-D2, D2-D2, AND D2-D3 EXCHANGE-COUPLED DIMERS

The syntheses and characterization of several isomorphous siloxy-bridged dimers with the general formula [(cC6H117Si7O12M-(C5H5N)2][(c-C6H11)7Si7O12M'] [3a (M = M' = Ti), 3b (M = M' = V), 3c,d (M ? M' = Ti, V), 3e (M = Cr, M' = V)] are reported. The metal ions in these magnetically dilute complexes are strongly antiferromagnetically coupled. Temperature-dependent magnetic susceptibility measurements on dimers possessing either two Ti(III) ions or two V(III) ions indicate that the metal ions are strongly antiferromagnetically coupled (-J >1000 cm-1for 3a and 80.5 cm-1for 3b). Attempts to prepare mixed-metal dimers containing one V(lil) ion and either one Ti(lll) or one Cr(III) ion led to solid solutions consisting of V(III)/V(III) dimers and either Ti(lII)/V(III) or Cr(Ill)/V(IIl) dimers. Analysis of the temperature-dependent susceptibility data for these mixtures provided best-fit antiferromagnetic exchange constants (-J) of 187 and 55 cm-1, respectively, for 3c,d and 3e. The observed correlation between-J and the number of unpaired spins on each metal ion is discussed. © 1990, American Chemical Society. All rights reserved.