pH-Dependent spin state population and F NMR chemical shift via remote ligand protonation in an iron(ii) complex.

An Fe complex that features a pH-dependent spin state population, by virtue of a variable ligand protonation state, is described. This behavior leads to a highly pH-dependent F NMR chemical shift with a sensitivity of 13.9(5) ppm per pH unit at 37 °C, thereby demonstrating the potential utility of the complex as a F chemical shift-based pH sensor.

Spin-crossover and high-spin iron(ii) complexes as chemical shift F magnetic resonance thermometers.

The potential utility of paramagnetic transition metal complexes as chemical shift F magnetic resonance (MR) thermometers is demonstrated. Further, spin-crossover Fe complexes are shown to provide much higher temperature sensitivity than do the high-spin analogues, owing to the variation of spin state with temperature in the former complexes. This approach is illustrated through a series of Fe complexes supported by symmetrically and asymmetrically substituted 1,4,7-triazacyclononane ligand scaffolds bearing 3-fluoro-2-picolyl derivatives as pendent groups (L ).

Electron Hopping through Double-Exchange Coupling in a Mixed-Valence Diiminobenzoquinone-Bridged Fe2 Complex.

The ability of a benzoquinonoid bridging ligand to mediate double-exchange coupling in a mixed-valence Fe2 complex is demonstrated. Metalation of the bridging ligand 2,5-di(2,6-dimethylanilino)-3,6-dibromo-1,4-benzoquinone (LH2) with Fe(II) in the presence of the capping ligand tris((6-methyl-2-pyridyl)methyl)amine (Me3TPyA) affords the dinuclear complex [(Me3TPyA)2Fe(II)2(L)](2+). The dc magnetic measurements, in conjunction with X-ray diffraction and Mössbauer spectroscopy, reveal the presence of weak ferromagnetic superexchange coupling between Fe(II) centers through the diamagnetic bridging ligand to give an S = 4 ground state.