Study of Spin-Crossover in Iron(II) Complexes with 2,6-Bis(4,5-Dimethyl-1H-Imidazol-2-yl)Pyridine and closo-Borate Anions

Abstract

New iron(II) coordination compounds with 2,6-bis(4,5-dimethyl-1H-imidazol-2-yl)pyridine (L) and closo-borate(2–) anions [FeL2]B10H10⋅2H2O and [FeL2]B12H12⋅H2O have been synthesized. The compounds have been identified and studied by CHN analysis, electron spectroscopy (diffuse reflection spectroscopy), IR, Mössbauer, and EXAFS spectroscopies, X-ray powder diffraction, and static magnetic susceptibility. The structures of the coordination knots of complexes [FeL2]B10H10⋅2H2O and [FeL2]B12H12⋅H2O has been obtained by modeling the EXAFS spectra. The ligand is coordinated by the iron(II) ion in a tridentate-cyclic manner by two nitrogen atoms of imidazole cycles and a nitrogen atom of pyridine to form the FeN6 coordination knot. The study of the temperature dependence of the magnetic susceptibility in the range of 80–500 K has showed that the high-temperature spin-crossover 1А1 ↔ 5Т2 manifests itself in the obtained compounds.

A DFT and Mössbauer spectroscopy investigation of spin‐crossover iron(II) complexes with 2,6‐bis(1H‐imidazol‐2‐yl)pyridines

“…The geometric parameters of the nearest coordination sphere of the iron ion (Table 1) indicate that the Fe(II) coordination spheres of complex cations are distorted octahedra with similar Fe-N distances for nitrogen atoms in axial and equatorial positions. Note that the Fe-N distances obtained for the [Fe(L m ) 2 ] 2+ complex cations agree with the EXAFS spectroscopy structural data for the [Fe(L m ) 2 ]A i ÁnH 2 O compounds [24][25][26][27].…”

“…It is these nine complexes that showed interesting regularities of experimental IS and QS values. The IS and MS parameters of L2 containing compounds (independently on A) exceed those of L1 and L3 containing compounds by <0.02> and <0.1> mm/s, respectively [24–27]. In the present work, this difference between the MS parameters is explained by means of quantum chemical computations and the IS and QS analysis for molecular complexes of iron(II) with 2,6‐bis(1 H ‐imidazole‐2‐yl)pyridines.…”

“…Since no detailed structural data have been ever reported for the considered three groups of compounds (each group containing the same complex cations) [24][25][26][27][28][29], we considered three complex cations [Fe(L m ) 2 ] 2+ (m = 1, 2, 3) without taking into account the environment (anions and water molecules). Note that the studied complex cations and their structural analogues are not included in the list of complexes considered in References [29][30][31][32][33].…”

“…(1H-imidazole-2-yl)pyridines [21]. We earlier reported a number of works devoted to the study of iron(II) complexes with 2,6-bis(1H-imidazole-2-yl)pyridine derivatives (Scheme 1) exhibiting the 1 A 1 $ 5 T 2 spin crossover [22][23][24][25][26][27].…”

“…The experimental error is shown in parentheses. a Experimental quadrupole splitting (QS) values according to[24][25][26][27].…”