ICYS, National Institute for Materials Science^* X-ray Physics Laboratory, National Institute for Materials Science, Tsukuba, Ibaraki, Japan^** HVEMS, National Institute for Materials Science, Tsukuba, Ibaraki, Japan^*** National Institute for Materials Science, Tsukuba, Ibaraki, Japan^****
○Pance Naumov^* Kenji Sakurai^** Toru Asaka^*** Alexei A. Belik^****

The structural grounds of the decrease of point and lattice symmetries coupled with switching of the exchange interaction in single crystals of highly strained, coordinationally unsaturated bisdiaminecopper(II) cation are described [1,2]. The combined magnetic susceptibility and X-ray diffraction results indicate that the interplay between the inherent vibronic instability and ligand field strain imposed by moderately flexible, coordinationally shielding ligands, enables effective switching of the pseudo-Jahn-Teller d⁹ centers between states with different exchange interaction in the low-temperature regime, and valence orbital orientation and coordination geometry in the high-temperature regime. Within the low-temperature hysteresis region, the phase transition can be also induced by excitation of the ligand-to-metal charge transfer bands, resulting in overall shrinkage of the lattice. The compound is a prototype of weakly electronically coupled one-dimensional Jahn-Teller systems which can undergo phase transitions induced by light, in addition to heating, cooling and change of pressure, and it represents a prospective basis for the design of switching materials capable of multimode external control.

[1] P. Naumov, K. Sakurai, T. Asaka, A. A. Belik, S. Adachi, J. Takahashi, S. Koshihara,
Inorg. Chem. 2006, 45, 5027.

[2] P. Naumov, K. Sakurai, T. Asaka, A. A. Belik, S. Adachi, J. Takahashi, S. Koshihara,
Chem. Comm. 2006, 1491.