High Field Magnetization and ESR Measurements on a Spin-Crossover Complex

Abstract

In this paper, we report the results of the high field magnetization and the high field/high frequency ESR measurements on [Mn III (taa)], which is a spin-crossover complex. The observed ESR signals will be discussed in connection with the results of our high field magnetization which exhibits the first observation of the field-induced spin-crossover transition.

ESR study of spin-crossover complex [MnIII(taa)] using pulsed high magnetic field

“…The result of the simulation clearly indicates the existence of the rhombic anisotropy E-term in the HS state of ½Mn III ðtaaÞ: From the X-ray crystallographic analysis at room temperature, the trigonal symmetry of the molecular structure of ½Mn III ðtaaÞ was reported [2]. As described in the previous papers [1,6,7], however, the Jahn-Teller instability arises in the HS state of Mn III ion under the trigonal symmetry, because the degeneracy of e g orbital cannot be lifted by the trigonal ligand field. Three equivalent distorted configurations of the molecular structure from the trigonal symmetry are expected to be arisen by the Jahn-Teller effect.…”

“…Such a disorder gives the entropy of DS ¼ R log 3 ¼ 9:13 J K À1 mol À1 that is almost equal to the excess entropy beyond the spin contribution of ½Mn III ðtaaÞ: The result of our ESR measurement is consistent with the existence of the Jahn-Teller distortion in the HS state of ½Mn III ðtaaÞ; since the E-term is not derived from the trigonal ligand field. It is interpreted that a time-averaged structure, corresponding to the trigonal one, is observed by the X-ray diffraction measurement, whereas the Jahn-Teller distortion is detected by the ESR measurement reflecting the characteristic frequency of the molecular reorientation slower than the ESR frequency at 77 K: The rapid broadening of the ESR signals with increasing temperature, reported in our previous paper [1], must result from the thermal activation of the molecular reorientation.…”

“…The d 4 spin-crossover complex ½Mn III ðtaaÞ (H 3 ðtaaÞ ¼ trisð1-ð2-azolylÞ-2-azabuten-4 À ylÞamine) is the first example exhibiting the spin-crossover transition induced by an external magnetic field [1]. This compound is known to show the thermally induced spin-crossover transition around T c B46 K between the low-spin (LS) state of S ¼ 1 and the high-spin (HS) one of S ¼ 2 [2,3].…”

Cooperative Spin Transition in a Mononuclear Manganese(III) Complex

“…At room temperature, χ m T =2.79 cm 3 mol −1 K ( S =2) with g =1.93, which persists on cooling to 132 K when it drops sharply to χ m T =1.25 cm 3 mol −1 K over a 4 K range with critical temperature T c ↓ =130 K. There is a further decrease to χ m T =1.09 cm 3 mol −1 K, with g =2.08 by 100 K, that is, full conversion to S=1, followed by a drop below 25 K owing to spin–orbit coupling. On warming, a similarly abrupt transition is observed but with T c ↑ =138 K, resulting in a thermal magnetic hysteresis loop of 8 K centered at 134 K, which is much wider than for the [Mn(pyrol) 3 tren] complex with the same type of magnetometer (1.6 K loop) 15d. The crossover profile was sensitive to particle size, as revealed by temperature‐cycling experiments on a second crystalline sample.…”

Spin crossover in[MnIII(pyrol)3tren]probed by high-pressure and low-temperature x-ray diffraction

“…If the first goal of our study is the determination of the high pressure behavior of this compound, the investigation of the low temperature structural properties is also of great interest. First, up to now, no Mn(III) complex has been structurally characterized in both high and low spin states.. Then, recent spectroscopic measurements have evidenced the presence of a dynamic Jahn Teller distortion in the HS phase [14][15][16] and questioned the role of the vibrational modes in the SCO behavior of this compound 15 .…”