Effects of the modulation of magnetic exchange interactions on the electron paramagnetic resonance spectra of some carboxylate-bridged oxovanadium(IV) dimers

Abstract

The fluid solution EPR spectra of [VO(L)(µ- L¹)VO(L)(dmpz)]· 2C₆H₅Me (I), [{VO(L)(dmpz)}₂(µ- L²)]· 2MeCN · 2H₂O (II) and [{VO(L)(dmpz)}₂(µ- 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- dimethylpyrazole] 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.