Abstract
The energies of the metal-to-ligand charge transfer (MLCT) and metal-to-metal charge transfer (MMCT) absorption bands of a no. of heterocycle-bridged diiron(II,II) homovalent and diiron(III,II) mixed-valent complexes correlate linearly with Gutmann's acceptor no. (AN). The compds. are (NEt4)6(NC)5Fe(m-tz)Fe(CN)5 and (NEt4)5(NC)5Fe(m-tz)Fe(CN)5, tz = 1,2,4,5-tetrazine; (NEt4)4(NC)4Fe(m-bptz)Fe(CN)4 and (NEt4)3(NC)4Fe(m-bptz)Fe(CN)4, bptz = 3,6-bis(2-pyridyl)-1,2,4,5-tetrazine; (NEt4)4(NC)4Fe(m-bmtz)Fe(CN)4, bmtz = 3,6-bis(2-pyrimidyl)-1,2,4,5-tetrazine; (NEt4)4(NC)4Fe(m-bpym)Fe(CN)4, bpym = 2,2'-bipyrimidine. Mononuclear analogs of the tz and bpym ligands were also studied. Various degrees of neg. and pos. solvatochromism are obsd. for centrosym. dinuclear systems. Unusual observations include the large neg. solvatochromism of MLCT bands in Fe(II)Fe(II) species lacking a permanent dipole moment, the pos. solvatochromism of MLCT/LMCT bands and the small neg. solvatochromism of MMCT bands in the valence-averaged Fe2.5Fe2.5 systems. on SciFinder(R)
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