Solution and Solid‐State Study of the Spin‐Crossover [Fe^II(R‐bik)₃](BF₄)₂ Complexes (R = Me, Et, Vinyl)

Abstract

Overall these experiments give coherent results with T1/2 located between 320 and 335 K, a narrow range in comparison to the solid-state. DFT calculations allowed rationalizing the differences in the magnetic differences. The molecular orbital and spin density calculations reveal that the presence of the C=O group between the imidazolyl units in the ligands of 1-3 leads to an extended aromatic system, an effective -acceptor effect, stabilizing a LS state and reducing the LS-HS gap in comparison to 4.

Thermally-Induced Spin Crossover and LIESST Effect in the Neutral [FeII(Mebik)2(NCX)2] Complexes: Variable-Temperature Structural, Magnetic, and Optical Studies (X = S, Se; Mebik = bis(1-methylimidazol-2-yl)ketone)

“…However we showed in a previous study that the presence of the CO group between the two imidazolyl groups confers some aromaticity to the Me bik ligand and thus, a π-acceptor character. (De et al, 2018) Here the dihedral angle between the imidazolyl rings are 24.9 ( 1 ) and 24.1° ( 2 ) at 200 K. These values are quite larger than those observed in the low-spin [Fe( Me bik) 3 ](BF 4 ) 2 (between ca. 4 and 11°) (De et al, 2018).…”

“…(De et al, 2018) Here the dihedral angle between the imidazolyl rings are 24.9 ( 1 ) and 24.1° ( 2 ) at 200 K. These values are quite larger than those observed in the low-spin [Fe( Me bik) 3 ](BF 4 ) 2 (between ca. 4 and 11°) (De et al, 2018). Finally the NCX ligands are linear (Tables S3, S4) however the Fe-N-C angle deviates significantly from linearity ( ca .…”

“…The reported output (shape factor) allows assessing the matching between an idealized polyhedron and actual coordination sphere: the lower the shape factor is, the better the matching between the actual coordination sphere and the idealized polyhedron. The analyses lead to numerical values of 0.85 for both 1 and 2 at 200 K (0 would correspond to a perfect octahedron), a value which is a bit larger than that observed in the low-spin [Fe( Me bik) 3 ](BF 4 ) 2 complex (0.42) (De et al, 2018). …”

“…However R bik ligands form six-membered chelate rings leading to weaker ligand field than for the five membered chelate rings observed in similar bipy and phen complexes. Thus, whereas [Fe II (L-L) 3 ] 2+ are a low-spin complexes, the [Fe II ( R bik) 3 ] 2+ are SCO complexes (De et al, 2018). The high-spin six-membered rings [Fe II ( R bik) 3 ] 2+ complexes are also more labile at room temperature in comparison to the inert [Fe II (L-L) 3 ] 2+ , which makes the preparation of bis-chelate complexes more easy.…”

“…Whereas the {Fe 2 Fe 2 } compound show a significant LIESST effect in the 700–900 nm range (only in the dehydrated phase), the {Fe 2 Mo 2 } shows the strongest increase of magnetization at 405 nm, whereas LIESST effect is much less significant at 800 nm. In contrast, the [Fe( Me bik) 3 ](BF 4 ) 2 monometallic complex shows a maximal effect at 635 nm (De et al, 2018). …”