A new approach to treating vibronic coupling under stress-The strain-induced enhancement or suppression of Jahn-Teller distortions in tetrahedral Cu~ⅡCl_4-complexes, and the transition to octahedral structures

摘要

Host-lattice and host-site properties play a distinct role in essentially modifying the electronic, but also the elastic properties of molecular compounds and of solids with copper(Ⅱ), which otherwise underlie the - usually dominating - symmetry and energy effects due to vibronic Jahn-Teller coupling. A symmetry-appropriate theoretical treatment, which closely follows the experiment, is suggested for CuCl_4~(2-)-complexes. It accounts for the observed widespread appearance of molecular distortions from close-to-tetrahedral to square-planar, and furthermore allows for the extension towards hexa-coordinate species. The significant conclusion is, that the imposed elastic strain plays an important role, whose consideration contributes to a better understanding of hitherto unexplained experimental phenomena, such as the unexpectedly weak dependence of the ground state stabilisation and of the charge-transfer energies on the extent of distortion away from T_d.