In contrary to customarily consideration of the Jahn-Teller theorem for 3d-ion compounds in the orbital space only we point out that it has to be considered in the spin-orbital space. It is despite the weakness of the intraatomic spin-orbit coupling. A direct motivation for this paper is an erroneous claim of a recent Phys. Rev. Lett. 96 (2006) 027201 paper that the high-spin t2g4eg2 state of the 3d6 configuration is not Jahn-Teller active.
Cite
@article{arxiv.cond-mat/0604207,
title = {The Jahn-Teller theorem for 3d ions and their compounds},
author = {R. J. Radwanski and Z. Ropka},
journal= {arXiv preprint arXiv:cond-mat/0604207},
year = {2007}
}