EFFECTS OF THE MODULATION OF MAGNETIC EXCHANGE INTERACTIONS ON THE ELECTRON-PARAMAGNETIC-RESONANCE SPECTRA OF SOME CARBOXYLATE-BRIDGED OXOVANADIUM(IV) DIMERS

The fluid solution EPR spectra of [VO(L)(mu-L1)VO(L)(dmpz)].2C6H5Me (I), [{VO(L)(dmpz)}2(mu-L2)].2MeCN.2H2O (II) and [{VO(L)(dmpz)}2(mu-L3)].1.2C6H5Me (III) [L = hydrotris(3,5-dimethylpyrazolyl)borato, H2L1 = malonic acid, H2L2 = acetylenedicarboxylic acid H2L3 = benzene-1,4-dicarboxylic acid, dmpz = 3,5-dimethypyrazole] in CH2Cl2, CH2Cl2-toluene, CH2Cl2-MeCN and CH2Cl2-MeOH mixtures, at X-band frequency, and over the temperature range 300-240 K are reported. The spectra are consistent with the dimeric formulations wherein there is an exchange interaction with \J\/\A\ > 1. In addition, the spectra exhibit unusual amplitude variations of the lines which are attributed to fluctuations in the exchange interactions.