A Unified Treatment of the Relationship Between Ligand Substituents and Spin State in a Family of Iron(II) Complexes. (1st March 2016)

• Record Type: Journal Article
• Authors: Kershaw Cook, Laurence J.; Kulmaczewski, Rafal; Mohammed, Rufeida; Dudley, Stephen; Barrett, Simon A.; Little, Marc A.; Deeth, Robert J.; Halcrow, Malcolm A.
• Is Part Of: Angewandte Chemie. Volume 128:Number 13(2016)
• Page Start: 4399
• Page End: 4403
• Publication Date: 2016-03-01
• Subjects: Dichtefunktionalrechnungen -- Eisen -- N-Liganden -- Spinzustände -- Substituenteneffekte; Chemistry -- Periodicals; 540
• DOI: 10.1002/ange.201600165
• Languages: English
• ISSNs: 0044-8249

Abstract

Abstract: The influence of ligands on the spin state of a metal ion is of central importance for bioinorganic chemistry, and the production of base‐metal catalysts for synthesis applications. Complexes derived from [Fe(bpp)2 ] 2+ (bpp=2, 6‐di{pyrazol‐1‐yl}pyridine) can be high‐spin, low‐spin, or spin‐crossover (SCO) active depending on the ligand substituents. Plots of the SCO midpoint temperature ( T 1 / 2 ) in solution vs. the relevant Hammett parameter show that the low‐spin state of the complex is stabilized by electron‐withdrawing pyridyl ("X") substituents, but also by electron‐donating pyrazolyl ("Y") substituents. Moreover, when a subset of complexes with halogeno X or Y substituents is considered, the two sets of compounds instead show identical trends of a small reduction in T 1 / 2 for increasing substituent electronegativity. DFT calculations reproduce these disparate trends, which arise from competing influences of pyridyl and pyrazolyl ligand substituents on Fe‐L σ and π bonding.