Thulium compounds state

TmETS Thulium ethylsulphate has hexagonal symmetry. The other compounds have tetragonal symmetry, except TmV04 and TmAs04, that have doublet states split by Jahn-Teller distortions below 2.156 K and 6.1 K, respectively (see section 6). These lower the symmetry and the constants given are extrapolated to T = OK. 

With thulium, for which the III state is still more stable, this trend manifests itself in an even more curious way. TmS and TmSe are semi-metallic compounds, derived from Tm(III), while TmTe is a derivative of Tm(II) (Bucher et al 1975). 

Smith, J.A.S., 1974, "Advances in Nuclear Quadrupole Resonance , vol. 1 (Heydon). Smith, W.C., 1971, High Frequency Nuclear Magnetic Resonance in Thulium Intermetal-lic Compounds", Ph.D. Thesis, Iowa State University (unpublished). 

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