Low-spin, mononuclear, Fe(III) complexes with P,N donor hemilabile ligands: A combined experimental and theoretical study

Two new mononuclear Fe(III) complexes, [FeCl3{PPh2(p-C6H4NMe2)-P}3](1) (PPh2(p-C6H4NMe2): 4-(dimethylamino)phenyldiphenylphosphine) and [FeCl3(PPh2py-P)(PPh2py-P,N)] (2) (PPh2py: diphenyl(2-pyridyl)phosphine) were synthesized by reacting anhydrous FeCl3 with respective ligand in acetonitrile solution under refluxing condition. Both the complexes were characterized by elemental analysis, FAB-Mass, FTIR, UV–Vis, ESR, Cyclic Voltammetry and magnetic measurement. The FAB mass spectra of complexes 1 and 2 show molecular ion peak at m/z 1078 [M]+ and m/z 687 [M−1]+, respectively, indicating mononuclear nature of the complexes. UV–Vis spectra of the complexes were consistent with low-spin, octahedral geometry. The variable temperature magnetic susceptibility measurement (73–323 K) of these complexes is also consistent with the paramagnetic nature of the complexes with a ground state spin S = ½. The Fe(III) centers of these two complexes remain low-spin, both at room temperature and liquid nitrogen temperature, was also indicated by the ESR analysis. Cyclic Voltammetry of both the complexes show an irreversible oxidation wave attributed to Fe3+ → Fe4+ + e− along with the peak for ligand oxidation. Theoretical calculations (B3LYP) of the complexes show that for complex 1, a trans geometry of the two phosphorous atoms and for complex 2, a mer,cis structures are the most favored geometrical isomer. TDDFT calculations were performed to interpret the observed bands in the UV–Visible spectra.

Two low-spin, mononuclear, Fe(III) complexes, with two P,N donor hemilabile ligands, were synthesized and characterized by elemental analysis, FAB-Mass, FTIR, UV–Vis, ESR, Cyclic Voltammetry and variable temperature magnetic measurements. Theoretical calculations (B3LYP) were performed to find out the most stable geometrical isomer of the complexes and also to interpret the UV–Vis spectra.Figure optionsDownload as PowerPoint slide