and o-phenylenediamide o-C6H4(NH):-. The most stable members of these redox series are the uncharged diamagnetic and deep-blue complexes M[o-C6H4(NH),JZ having two mutually coupled o-semiquinonediimine ligands. One-electron oxidation of the neutral complexes leads to the cations MIo-C6H4(NH),] s, with loss of one ligand electron. This can be deduced, inter alia, from the fact that the potentials of the oxidation are almost independent of the metal and the unpaired electron of the cations is localized on the ligand~'~]. We observed that this ligand oxidation also occurs as a photochemical reaction. The complexes of Ni and Pt were studied in detaiI.
solution of (1) in acidic methanol appears at 339 nm, while the photohydrolysis product absorbs at 340 nm in acid mediac2=l. This small difference allows no conclusions about the configuration of the double bond in the photohydrolysis product, as the difference for the E,E-and 2,Z-isomers of 2,4-hexadienoic acidr4] is also only 5 nm. According to its 'H-NMR spectrum, (1) is present mainly in the E,Econfiguration [(la) J2,3 = 14, J4,5 = 12 Hz; cf. analogous dialkylamino compoundsrs1]. The 2E,4Z-compound (lb) (J,,3 = 14.5, J4.5 = 8 Hz) is detectable as minor component
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