For 10 points -- name the effect in which a molecule in a degenerate state is unstable relative to a nondegenerate configuration of lower symmetry.
The greatest body of data available about this effect concerns copper (II) compounds. It is chiefly seen in high-spin d4, low-spin d7, and d9 configurations, in all of which the t sub 2g orbitals of octahedrally coordinated metal ions are all equally occupied, giving rise to a doubly degenerate ground state, and thus a distortion in the octahedron, often seen as an elongation along one of the four axes, with extreme cases causing a full distortion to a square planar complex. For 10 points -- name the effect in which a molecule in a degenerate state is unstable relative to a nondegenerate configuration of lower symmetry.
The greatest body of data available about this effect concerns copper (II) compounds.
(Landau-)Jahn-Teller effect