ADIABATIC POTENTIAL OF THE SYSTEM OF 2 EQUIVALENT VIBRONIC CENTERS WITH COMMON ATOMS .2. EQUILIBRIUM NUCLEAR CONFIGURATIONS OF THE BIOCTAHEDRAL SYSTEMS

The two-centre Jahn-Teller effect for edge- and face-shared bioctahedr a with a vibronic E(g) x e(g) interaction at each centre is considered . The lowest sheet of the adiabatic potential of these systems is inve stigated using the one-centre-coordinate approach. It is shown that th e intercentre correlation of the Jahn-Teller distortions is of great i mportance in these systems. This correlation is determined by the inte rcentre elastic interaction and, implicitly, by the coupling condition s imposed on the one-centre nuclear coordinates as a result of the pre sence of common atoms in the bioctahedra. Owing to the intercentre cor relation, non-Jahn-Teller distortions of individual octahedra arise to gether with the Jahn-Teller distortions. The resulting equilibrium nuc lear configurations of the bioctahedra are compared with those observe d in the low-symmetry structure phase of the CuX2(NH3)2 distortion iso mers and the hexagonal perovskites ACuCl3.