Synthesis and Magnetic Studies of Two Neutral, Bis-Ligand Fe(II) Complexes Containing Carbazole-Bis(tetrazole) Ligands

Previously reported carbazole-bis(tetrazole) (CzT(R)) ligands (where R = iPr and CH2-2,4,6-C6H2Me3) were used to synthesize air-stable, six-coordinate, octahedral bis-ligand Fe(II) complexes (CzT(R))(2)Fe. The synthesis and characterization of these complexes using H-1 nuclear magnetic resonance (NMR), X-ray crystallography, Mossbauer spectroscopy, and density functional theory (DFT) calculations are reported. Analysis of the magnetic properties revealed that the isopropyl derivative displays thermally induced spin crossover (SCO) over a temperature range of 150-350 K. This transition appears as an abrupt two-step transition in the solid state but simplifies to a smooth one-step transition in solution. The two-step transition in the solid state has been postulated to be due to lattice and solvation effects. In contrast, the slightly bulkier substituted CH2-2,4,6-C6H2Me3 (CH(2)Mes) Fe complex displays dramatically different magnetic behavior with no SCO and magnetic data suggesting low-spin Fe(II) with a possible TIP contribution. DFT calculations support the postulate that the change in magnetic behavior is primarily due to the nature of the ligand substituents.

Automated summary

Previously reported carbazole-bis(tetrazole) (CzT(R)) ligands (where R = iPr and CH2-2,4,6-C6H2Me3) were used to synthesize air-stable, six-coordinate, octahedral bis-ligand Fe(II) complexes (CzT(R))(2)Fe. The synthesis and characterization of these complexes using H-1 nuclear magnetic resonance (NMR), X-ray crystallography, Mossbauer spectroscopy, and density functional theory (DFT) calculations are reported. The magnetic properties of the isopropyl derivative exhibit thermal induced spin crossover (SCO) while the slightly bulkier CH2-2,4,6-C6H2Me3 (CH(2)Mes) Fe complex shows different magnetic behavior with no SCO.