Effect of Chelate Ring Size in Iron(II) Isothiocyanato Complexes with Tetradentate Tripyridyl‐alkylamine Ligands on Spin Crossover Properties

Abstract

Iron(II) complexes of the type [Fe(L)(NCS) 2 ] with tetradentate ligands L are well known to show spin crossover properties. However, this behavior is quite sensitive in regard to small changes of the ligand system. Starting from the thoroughly investigated complex [Fe(tmpa)(NCS) 2 ] [tmpa = tris(2-pyridylmethyl)amine, also abbreviated as tpa in the literature] we modified the ligand by increasing systematically the chelate ring sizes from 5 to 6 thus obtaining complexes [Fe( 85(2-pyridyl)ethyl]amine]. All complexes were structurally characterized and spin crossover properties were investigated using Mößbauer spectroscopy, magnetic measurements, and IR/Raman analyses. The results demonstrated that only the iron complexes with tmpa and pmea showed spin crossover properties, whereas the complexes with the ligands pmap and tepa only formed high spin complexes. Furthermore, DFT calculations supported these findings demonstrating again the strong influence of ligand environment. Herein the effect of increasing the chelate ring sizes in iron(II) isothiocyanato complexes with tetradentate tripyridyl-alkylamine ligands is clearly demonstrated. Figure 6. 57 Fe-Mößbauer spectra of 2 under continuous red light irradiation (820 nm; 40 mW·cm -2 ) and without irriadiation between 170 and 200 K. Clearly the reverse LiPTH effect is observed and indicates a higher cooperativity among the centers. more, Brehm et al. found a detectable shift due to motion of the pyridine skeleton. The two C=C stretching modes gave rise to two well-separated, moderately intense bands at 1571/ Z. Anorg. Allg. Chem. 2016, 85-94 89 1603 cm -1 (IR) and 1572/1604 cm -1 (Raman), respectively, in the HS state. Within the Raman spectrum five bands in the range 50-100 cm -1 could be detected from the LS complex, ARTICLE

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