1,2-bis(pyridine-2-carboxamido)benzenate(2-), (bpb)(2-): A noninnocent ligand. Syntheses, structures, and mechanisms of formation of [(n-Bu)(4)N][Fe-2(IV)(mu-N)(bpb)(2)(X)(2)] (X = CN-, N-3(-)) and the electronic structures of [M-III(bpb(ox1))(CN)(2)

摘要

The well-known tetradentate ligand 1,2-bis(pyridine-2-carboxamido)benzenate(2-), (bpb)(2-), and its 4,5-dichloro analogue, (bpc)(2-), are shown to be "noninnocent" ligands in the sense that in coordination compounds they can exist in their radical one- and diamagnetic two-electron-oxidized forms (bpb(ox1))(-) and (bpb(ox2))(0) land (bpc(oX1))(-) and (bpc(ox2))(0)), respectively. Photolysis of high-spin [(n-Bu)(4)N][Fe-III(bpb)(N-3)(2)] and its (bpc)(2-) analogue in acetone solution at room temperature generates the diamagnetic dinuclear complex [(n-Bu)(4)N][Fe-2(IV)(mu-N)(bpb)(2)(N-3)(2)] and its (bpc)(2-) analogue; the corresponding cyano complex [(n-Bu)(4)N][Fe-2(IV)(mu-N)(bpb)(2)(CN)(2)] has been prepared via N-3(-) substitution by CN-. Photolysis in frozen acetonitrile solution produces a low-spin ferric species (S = 1/2) which presumably is [Fe-III(bpb(ox2))(N)(N-3)](-), as has been established by EPR and Mossbauer spectroscopy. The mononuclear complexes [(n-Bu)(4)N][Fe-III(bpb)(CN2)] (low spin), [Et4N][Co-III(bpb)(CN)(2)] and Na[Co-III(bpc)-CN)(2)].3CH(3)OH can be electrochemically or chemically one-electron-oxidized to give [Fe-II(bpb(ox1))(CN)(2)](0) (S = 0), [Co-III(bpb(ox1))(CN)(2)](0) (S = 1/2), and [Co-III(bpc(ox1))(CN)(2)](0) (S = 1/2). All complexes have been characterized by UV-vis, EPR, and Mossbauer spectroscopy, and their electro- and magnetochemistries have been studied. The crystal structures of [(n-Bu)(4)N][Fe-III(bpb)(N-3)(2)].1/2C(6)H(5)CH(3), Na[Fe-III(bpb)(CN)(2)], Na[Co-III(bpc)(CN)(2)].3CH(3)OH, [(n-Bu)(4)N][Fe-2(IV)(mu-N)(bpb)(2)(CN)(2)], and [(n-Bu)(4)N][Fe-2(IV)(mu-N)(bpb)(N-3)(2)] have been determined by single-crystal X-ray diffraction. [References: 28]