文摘
Electronic structure theory predicts that, depending on the strength of the ligand field, either the quintet (5T2) or triplet (3T1) term states can be stabilized as the lowest-energy ligand-field excited state of low-spin octahedral d6 transition-metal complexes. The 3T1 state is anticipated for second- and third-row metal complexes and has been established for certain first-row compounds such as [Co(CN)6]3鈥?/sup>, but in the case of the widely studied FeII ion, only the 5T2 state has ever been documented. Herein we report that 2,6-bis(2-carboxypyridyl)pyridine (dcpp), when bound to FeII, presents a sufficiently strong ligand field to FeII such that the 5T2/3T1 crossing point of the d6 configuration is approached if not exceeded. The electrochemical and photophysical properties of [Fe(dcpp)2]2+, in addition to being of fundamental interest, may also have important implications for solar energy conversion strategies that seek to utilize earth-abundant components.