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Structural Basis for the Phase Switching of Bisaminecopper(II) Cations at the Thermal Limits of Lattice Stability

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posted on 26.06.2006, 00:00 by Panče Naumov, Kenji Sakurai, Toru Asaka, Alexei A. Belik, Shin-ichi Adachi, Junichi Takahashi, Shin-ya Koshihara
The structural grounds of the decrease of point and lattice symmetries coupled with switching of the exchange interaction in single crystals of a highly strained, coordinationally unsaturated bisdiaminecopper(II) cation are described. 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 also be 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.