A Unified Treatment of the Relationship Between Ligand Substituents and Spin State in a Family of Iron(II) Complexes |
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| Authors: | Dr Laurence J Kershaw?Cook Dr Rafal Kulmaczewski Dr Rufeida Mohammed Stephen Dudley Simon A Barrett Dr Marc A Little Prof Robert J Deeth Prof Malcolm A Halcrow |
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| Institution: | 1. School of Chemistry, University of Leeds, Leeds, UK;2. Department of Chemistry, University of Bath, Claverton Down, Bath, UK;3. Department of Chemistry, University of Liverpool, Liverpool, UK;4. Inorganic Computational Chemistry Group, Department of Chemistry, University of Warwick, Coventry, UK;5. School of Chemistry, University of Edinburgh, Joseph Black Building, Edinburgh, UK |
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| 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 ) 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 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. |
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| Keywords: | density functional calculations iron N ligands spin state substituent effects |
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