Magnetic properties of RbBp.2Ttg

Abstract

The crystal structure of RbBp.2Ttg (Bp = biphenyl and Ttg = Tetraglyme = CH₃O(CH₂CH₂O)₄CH₃) shows the presence of layers of paramagnetic biphenyl anions separated by layers of alkali-glyme complexes. This structure suggests two-dimensional magnetic behaviour. The magnetic properties of these crystals were studied with E.P.R. in the temperature range from 300 to 1·2K. Above 25K the anisotropy in the linewidth of the exchange-narrowed E.P.R. line and the deviations from the lorentzian lineshape demonstrate the importance of spin diffusion. Both results are in agreement with theoretical predictions made for pseudo 2-d magnetic systems. In the magnetic layer two biphenyl anions are lying closely together while all the others are further apart. This is reflected in the susceptibility which may be described by the singlet-triplet model with J = -13K. Upon cooling no E.P.R. signals of isolated triplets are observed. Instead, at 1·2 K a well resolved spectrum arises, which could be ascribed to isolated biphenyl anions in the doublet state. The spectra can be simulated perfectly. From the simulations we could conclude that the biphenyl anions are oriented according to the crystal structure. The concentration of the anions is about 1 per cent. An explanation of their occurrence is given. At high microwave powers a double quantum transition was observed in the temperature range from 3 to 7 K. This has been attributed to a transition from the |-1> to the |+1> state of the triplet manifold. It gains a high probability at orientations where the dipolar interaction is zero (‘magic angle’).