Dielectric behavior of manganese(III) spin-crossover complex [Mn(taa)]

Paraelectric behavior due to a dynamic Jahn-Teller (JT) effect is reported for the manganese(III) spin-crossover complex [Mn(taa)] [H₃taa=tris(1-(2-azolyl)-2-azabuten-4-yl)amine] in the high-spin (HS) phase above Tc=48K. The dielectric constant obeys the Curie-Weiss law with an asymptotic Curie temperature 26 K, suggesting competition between a low-spin (LS) phase and a ferrodistortively ordered (FO) phase at low temperatures. A phase diagram based on a four-state Ising-Potts model incorporating both a virtual cooperative JT transition (HS↔FO) and a spin-crossover transition (HS↔LS) is proposed to elucidate the interrelation of the HS, LS, and FO phases.