Dunsford, Jay J.Evans, David J.Pugh, ThomasShah, Sachin N.Chilton, Nicholas F.Ingleson, Michael J.2025-06-112025-06-110276-7333Bibtex:dunsford_three-coordinate_2016https://hdl.handle.net/1885/733758121A sterically demanding seven-membered expanded ring N-heterocyclic carbene (NHC) ligand allows access to rare examples of three-coordinate iron(II)−NHC complexes incorporating only halide coligands of the general formula [Fe(NHC)X2] (NHC = 7-DiPP; X = Br (1)Cl (2)). Reducing the steric influence of the ancillary NHC ligand through modulation of the N-aryl substituents leads to either four- or three-coordinate complexes of the general formula [Fe(NHC)Br2(THF)] (3) or [Fe(NHC)Br2] (4) (NHC = 7-Mes), dependent upon the solvent of recrystallization. The further reduction of NHC steric influence results in four-coordinate geometries at iron in the form of the dimeric species [Fe(NHC)Br(μ-Br)]2 (5) or [Fe(NHC)Br2(THF)] (6) (NHC = SDiPP), again dependent upon the solvent of recrystallization. Compounds 1−6 have been analyzed by 1H NMR spectroscopy, X-ray crystallography, elemental microanalysis, Mossbauer spectroscopy (for 1 and 3−5), and Evans method magnetic susceptibility. In addition to these measurements the three coordinate species 1 and 4 have been further analyzed by SQUID magnetometry and CASSCF calculations, which show significant magnetic anisotropy that is extremely sensitive to the coordination geometry9en2016-02-1410.1021/acs.organomet.6b0012184969542779