Synthesis, characterization, DFT calculations, and reactivity study of a nitrido-bridged dimeric vanadium(iv) complex

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)₂Fe. The synthesis and characterization of these complexes using ¹H 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 CH₂-2,4,6-C₆H₂Me₃ (CH₂Mes) 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.

Synthesis and characterization of trigonal bipyramidal FeIII complexes and their solution behavior

A series of air-stable trigonal bipyramidal Fe^III complexes supported by a redox non-innocent NNN pincer ligand, Cz ^tBu(Pyr^R)₂ ^- (R = iPr, Me, or H), were synthesized, fully characterized, and utilized for the investigation of the interaction between acetone and the Fe^III center. The magnetic moments determined from the paramagnetic ¹H NMR spectra in conjunction with EPR and Mössbauer spectroscopy indicate the presence of a high-spin ferric center. Cyclic voltammetry studies feature two quasi-reversible events corresponding to a metal-centered Fe^III/II reduction around -0.40 V (vs. Fc) and a ligand-centered Cz ^tBu(Pyr^R)₂/Cz ^tBu(Pyr^R)₂ ^•+ oxidation at potentials near +0.70 V (vs. Fc). UV-Visible spectroscopy in CH₂Cl₂ showcases ligand-metal charge transfer (LMCT) bands, as well as coordination of acetone to Cz ^tBu(Pyr^H)₂FeCl₂. In situ IR spectroscopy and solution conductivity (κ) measurements of Cz ^tBu(Pyr^R)₂FeCl₂ with varied equivalents of acetone reveal that acetone is weakly associated with the iron center.