Magneto-structural correlation in the Jahn-Teller isomers of Mn-12

In this Feature Article, we discuss our work on the Jahn - Teller isomers in a single molecule magnet, [Mn12O12(RCO2)(16)(H2O)(4)] ( abbreviated as Mn12R), and the magneto-structural correlation between them. Mn12R derivatives always exhibit two peaks at 5 and 2 K in the temperature dependence of the imaginary component of the ac susceptibility chi, suggesting the presence of a slower relaxation (SR) process and a faster relaxation (FR) process. Although the peak at 2 K used to be regarded as an impurity effect due to its weakness, recent studies have revealed that it is caused by a Jahn - Teller isomer. Most of the Mn12R crystals are now recognized as mixed crystals of SR and FR molecules having a structural difference in the Jahn - Teller distortion at Mn3+. In the SR molecule, the elongated Jahn - Teller axes of Mn3+ ions are all nearly parallel to the molecular axis of Mn12R, while the FR molecule includes an Mn3+ site of unusual Jahn - Teller distortion. The angular-dependent magnetic measurements on Mn12Ph indicated that the magnetic easy axis of the FR species was tilted by 12 degrees from the pseudo-D-4h molecular axis, while that of the SR molecule was parallel to it. High pressure was found to bring about a transformation of the SR species into FR even in Mn12Me, in which the number of FR species was negligible at ambient pressure. The structural and magnetic studies on a nearly 1 : 1 mixed crystal of Mn11CrMe and Mn12Me indicated that the magnetic anisotropy of Mn11CrMe was nearly identical to that of Mn12Me, though Mn11CrMe included a non-Jahn-Teller ion Cr3+ in the molecular skeleton of Mn12.