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 CH 2 -2,4,6-C 6 H 2 Me 3 ) 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 1 H nuclear magnetic resonance (NMR), X-ray crystallography, Mössbauer 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 CH 2 -2,4,6-C 6 H 2 Me 3 (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.