An electronic spectral study of some Fe(II) magnetic isomers in solution and a spectral-structural correlation with their Ni(II) analogs

[摘要] Pseudooctahedral Fe(II) Complexes of the hexadentate ligand, tris4-[(6-R)-2-pyridyl]-3-aza-3-butenylamine, where R is either H or CH^ (Figure 1) , have been studied in solution by electronic spectroscopy. The complexes represent a magnetically interesting series with Fe-I being low-spin, Fe-IV high-spin, and Fe-II and Fe-III spin equilibrium species. The d-d electronic spectrum of high-spin Fe-IV has been interpreted in terms of a strongly distorted octahedral ligand field model with 1 Dq = 11,4 cm. As evidenced by X-ray structural results, a major contribution of the reduction from symmetry appears to arise from a static molecular distortion in which the average Fe-N(imine) and Fe-N(pyridine) bond distances differ by .14. As for other low-spin tris(a-diimine)Fe(II) complexes, the spectrum of Fe-I is characterized by only Fe (II) -» l igand charge transfer bands whose intensities and positions obscure any d-d transitions. The spectrum of the spin equilibrium Fe-III compound displays features commensurate with a molefraction-weighted population of both high-spin and low-spin magnetic isomers with 1Dqhs (Fe-III) being ~11,7 cm-1 when the two spin states are nearly equi-energetic. The analogous Ni(II) complexes of Figure 1 have also been synthesized and characterized by elemental analysis, infrared spectroscopy, and solution conductivity, magnetic susceptibility, pmr, and d-d electronic spectral measurements. From the spectral studies, 1Dq values for the series are found to increase according to the sequence: Ni-IV (1,55 cm-1)

[发布机构] Rice University