Electronic Structure and Slow Magnetic Relaxation of Low-Coordinate Cyclic Alkyl(amino) Carbene Stabilized Iron(I) Complexes

Cyclic
alkyl­(amino) carbene stabilized two- and three-coordinate
Fe­(I) complexes, (cAAC)2FeCl (2) and [(cAAC)2Fe]­[B­(C6F5)4] (3), respectively, were prepared and thoroughly studied by a bouquet
of analytical techniques as well as theoretical calculations. Magnetic
susceptibility and Mössbauer spectroscopy reveal the +1 oxidation
state and S = 3/2 spin ground state of iron in both
compounds. 2 and 3 show slow magnetic relaxation
typical for single molecule magnets under an applied direct current
magnetic field. The high-frequency EPR measurements confirm the S = 3/2 ground state with a large, positive zero-field splitting
(∼20.4 cm–1) and reveal easy plane anisotropy
for compound 2. CASSCF/CASPT2/RASSI-SO ab initio calculations using the MOLCAS program package support the experimental
results.