ELECTRONIC MAGNETIC-RESONANCE IN A SERIES OF ANTIFERROMAGNETIC MOLECULAR PEROVSKITES

The magnetic properties of a series of ternary tetrathiafulvalenium (T TF+) salts incorporating, within a unique antiperovskite structure, a discrete halide (Y = Cl-, Br- or I-) in addition to an octahedral moly bdenum halide cluster dianion Mo6X142- (with X = Cl or Br), are descri bed. The preparation and structural chemistry of the materials of gene ral formula (TTF.+)3 (Mo6X142-)(Y-) are briefly recalled. The single-c rystal electronic magnetic resonance is explored in details using an X -band ESR spectrometer, both in the paramagnetic state where a narrow EPR signal is observed, as well as in the low temperature antiferromag netic phase where antiferromagnetic resonance (AFMR) is detected. A qu antitative discussion of the resonance field and linewidth is given in both regimes. The EPR line characteristics are shown to be strongly s ensitive to the TTF.+ environment, namely, the nature of the halide on both anion sites and small variations in intermolecular interactions, which reveal the importance of the spin-orbit coupling. On the other hand, AFMR data are discussed in terms of a dominant dipole-dipole int eraction as found previously for other TTF-based cation radical salts. Finally, similar albeit contrasted results are obtained with the isom orphous, chalcohalide rhenium cluster dianion-based ternary salt (TTF. +), (Re6S6Cl82-)(Cl-), which allow for a discussion of the AFMR linesh ape.