Tris-homoleptic complexes of Fe(II) with bisimidazole (bim) are known to exist only in the paramagnetic high-spin (HS) state, which in general places bim in the range of weak-field ligands. We have recently demonstrated [1] that a combination of bim with a stronger tetradentate ligand, tris(2-pyridylmethyl)amine (tpma), affords a heteroleptic complex [Fe(tpma)(bim)](ClO4)2 that undergoes spin-crossover (SCO) between the HS and low-spin (LS) states. In the course of this study we also discovered SCO behavior for the analogous complex [Fe(tpma)(xbim)](ClO4)2 with N-alkylated ligand, 1,1'-(a,a'-o-xylyl)-2,2'-biimidazole (xbim). Optical absorption studies also revealed that xbim was a slightly stronger ligand than bim. Now we report that the use of three xbim-type ligands results in the sufficient increase in the ligand-field strength to push the resulting tris-homoleptic complexes with Fe(II) into the SCO range. The complexes exhibit interesting crystal packing with important intermolecular interaction between the xbim ligands that should influence the abruptness of the spin transition.1. Phan, H.; Chakraborty, P.; Chen, M.; Calm, Y. M.; Kovnir, K.; Keniley, L. K.; Hoyt, J. M.; Knowles, E. S.; Besnard, C.; Meisel, M. W.; Hauser, A.; Achim, C.; Shatruk, M. Chem. Eur. J. 2012 , 18, 15805.

From bisimidazole to N-alkylated bisimidazoles: The incremental ligand field increase leads to spin crossover in homoleptic Fe(II) complexes

247th National Meeting (2014)

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