High‐Spin Mononuclear Iron(III) Complexes with Pentadentate Schiff Base Ligands: Structural Analysis and Magnetic Properties

Abstract

Various substituted 2-hydroxybenzophenones were combined with aliphatic linear triamines to form pentadentate Schiff base ligands. Twelve new iron(III) complexes with the general formula [Fe(L n )X].mCH 3 CN (n = 1-10; X = N 3 À , NCS À or NCSe À ; m = 0-2) have been synthesized, and spectrally as well as structurally characterized. The structural analysis revealed a notable dependence of coordination polyhedra deformation as well as the spatial configuration of donor atoms on the length and symmetry of the Schiff base ligands. The magnetic proper-ties of the compounds were investigated and the permanent high-spin state (S = 5/2) for all reported compounds was established, and allowed calculation of zero-field-splitting parameters as well as coupling constants, which were further confirmed with DFT calculations. The solid-state EPR spectra were recorded at 293 K and 98 K, and in accordance with the magnetic measurements, showed a high-spin state in the measured temperature range.[a] Dr.

Dinuclear Zn(II) and tetranuclear Co(II) complexes of a tetradentate N2O2 Schiff base ligand: Synthesis, crystal structure, characterization, DFT studies, cytotoxicity evaluation, and catalytic activity toward benzyl alcohol oxidation

“…Complex 2, however, showed low-intensity bands in the range of 550-700 nm due to its expected d-d transitions. 1 H NMR spectra of the H 2 L ligand and its zinc complex were recorded at 298 K in DMSO-d 6 (Figures S1 and S2). In the 1 H NMR spectrum of the ligand, the protons' broad peaks of phenolic OH 8 and OH 6 moieties were observed at 12.9 and 10.8 ppm, respectively.…”

“…Schiff base ligands are prepared easily and can be readily modified, both electronically and sterically . Schiff base ligands contain multiple potential donor sites, which allow them to bind metal ions with diverse coordination geometries such as bidentate and tridentate . Tetradentate Schiff base ligands also provide a suitable coordination platform for metal ions to provide diverse metallic complexes …”

“…[1,2] Schiff base ligands contain multiple potential donor sites, which allow them to bind metal ions with diverse coordination geometries such as bidentate and tridentate. [3][4][5][6] Tetradentate Schiff base ligands also provide a suitable coordination platform for metal ions to provide diverse metallic complexes. [7][8][9][10] Salpn-type Schiff base ligands are an interesting class of tetradentate ligands with four donor sites (N 2 O 2 ).…”

Three novel mononuclear 4‐vinylpyridine‐based Fe(III) complexes displaying various spin‐crossover behaviour

“…This affects the cooperativeness of the complex when SCO occurs, resulting in all complexes exhibiting a permanent HS state. [30] In this work, the pentadentate Schiff base ligands have been chemically modified with methyl and methoxy groups to obtain three complexes with different SCO behaviour. The magnetic properties indicated that when the H atom of the amino nitrogen was substituted by an electron-donating methyl group, the SCO temperature of the complex would move to a lower temperature.…”

“…However, One advantage of using pentadentate Schiff base ligands to synthesize SCO compounds is that auxiliary ligands or bridging ligands can be used to replace the sixth unstable coordination site to achieve fine regulation of SCO complexes. [28][29][30] For example, Matsumoto's group synthesized SCO complexes [Fe III (4-NH 2 py)L]BPh 4 , (4-NH 2 py = 4-aminopyridine; L = pentadentate Schiff base ligand) to study the effect of one-dimensional chain structure composed of hydrogen bonds on the steepness of SCO. [31] Subsequently Xu et al synthesized complexes [Fe(L)(py)] and [Fe(L)(dmap)](BPh 4 ) (L = N,N'-bis(2-hydroxybenzyliden)-1,7-diamino-4-azaheptane; dmap = 4-dimethylaminopyridine) using pentadentate Schiff base ligands and pyridine like ligands.…”