Spin-crossover thermal hysteresis and light-induced effect on iron(II) complexes with tripodal tris(2-pyridyl)methanol

Abstract

The X-ray crystal structure of Me4N[Fe(py3COH)(NCS)3](1-PrOH)0.5(H2O)2 [1; py3COH stands for tris(2-pyridyl)methanol] was successfully determined, clarifying that the complex has a pseudo-trigonal molecular arrangement, though the space group was P1¯. Possible π–π interaction is operative between the pyridine rings from neighboring [Fe(py3COH)(NCS)3]− ions. After annealing of 1 at 400K, the resultant compound was characterized to be Me4N[Fe(py3COH)(NCS)3](H2O) (1′), which showed a relatively abrupt spin-crossover (SCO) with thermal hysteresis. Combining the differential thermal analysis results, the SCO temperatures were determined as T1/2↓=224K and T1/2↑=246K. Compound 1′ also showed light-induced excited spin-state trapping (LIESST), as indicated with the χmT increased to a 32% level of the high-spin moment upon Xe-lamp irradiation at 5K. The LIESST effect disappeared at around 26K on heating. The complex ion [Fe(py3COH)(NCS)3]− is a rare anionic SCO and LIESST building block.