SUPPRESSION OF THE JAHN-TELLER EFFECT IN CHIRAL COPPER(II) AND CHROMIUM(II) OXALATE BRIDGED NETWORK STRUCTURES. Helmut W. Schmalle, Silvio Decurtins, Rene Pellaux, Mario Graf, Institute for Inorganic Chemistry, University of Zurich, Switzerland

Chiral three-dimensional (3D) framework structures consisting of tris-bipyridyl-metal complexes which function as chiral templates for the collective linking of metal ion centers through bis-chelating oxalate bridges have recently been described [1,2]. These compounds combine fundamental structural interest with potentially useful properties. They may afford supramolecular host-guest materials which can be tailored and functionalized for specific molecular-based magnetic and photophysical properties. Perceiving that the published structural results of the homometallic 3D compounds for the divalent 3d metal ions have been confined so far to Mn(II) and Fe(II), we attempted to prepare and investigate the analogous compounds with Cr(II) and Cu(II). Both, the high-spin d⁴ and the d⁹ system have in common that their ground state is described by an orbitally degenerate electronic state, ⁵E_g and ²E_g (in O_h symmetry), thus the ions are subject to the Jahn-Teller effect. Whereas for copper(II) systems a lot of supporting data describe the occurrence of a Jahn-Teller distortion, there are substantially fewer data for high-spin chromium(II) [3,4]. For the presented cubic Cu(II) and Cr(II) network structures anisotropic displacement parameters and metal-oxygen distances are compared with the refined tetragonal (P4₁2_l2) and orthorhombic (P2_l2_l2_l) subgroup structures of the Cu(II) compound, and are discussed in relation to the suppressed Jahn-Teller effect.

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[2] Decurtins, S., Schmalle, H. W., Pellaux, R. Schneuwly, P. & Hauser, A. (1996). Inorg. Chem. in press.

[3] Cotton, F. A., Daniels, I. M. & Murillo, C. A. (1993). Inorg. Chem. 32, 4868-4870.

[4] Akesson, R., Pettersson, L. G. M., Sandstrom, M. & Wahlgren, U. (1994). JACS 116, 8691-8704.