Different orbital occupation by an added single electron in 1,10-phenanthroline and its 3,4,7,8-tetramethyl derivative. Evidence from electron paramagnetic resonance spectroscopy of the anion radicals and of their dimesitylplatinum(II) complexes. X-ray molecular structure of dimesityl(1,10-phenanthroline)platinum(II)

, , , und . Journal of the Chemical Society, Perkin Transactions 2: Physical Organic Chemistry (1995)


In contrast to the anion radicals of 1,10-phenanthroline (phen) or its 4,7-di-Me deriv. (dmphen) with their 2B1 ground state, the 3,4,7,8-tetra-Me deriv. tmphen·- has a 2A2 ground state as evident from EPR/ENDOR measurements. The small p spin population at the potentially metal-coordinating nitrogen centers in the 2A2 species as opposed to the 2B1 state causes distinct spectroscopic effects in corresponding diorganoplatinum(II) complexes. The neutral compd. (phen)PtMes2, mes = mesityl, has been structurally characterized as a square planar PtII complex with tightly protected axial sites: monoclinic, space group P21/c, Z = 4, a = 9.378(1), b = 15.791(2), c = 16.581(1) \AA, b = 103.18(1)°. All complexes (NLN)PtMes2, NLN = bpy (2,2'-bipyridine), phen, tmphen, dppz (dipyrido3,2-a:2',3'-cphenazine) and pdo (1,10-phenanthroline-5,6-dione) are oxidized to EPR-silent platinum(III) species and reduced to anion radical complexes. The latter clearly contain PtII and heterocyclic anion radical ligands; however, they exhibit a trichotomous EPR behavior. Whereas the radical complex (phen)PtMes2·- shows a rather low giso-value of 1.983 and distinct g anisotropy in frozen soln. like the analogous complex of bpy·-, the formally related (tmphen)PtMes2·- has an isotropic g-factor (2.0030) much closer to the free-electron value and a distinctly smaller g anisotropy. The phenanthroline-derived radical complexes (pdo)PtMes2·- and (dppz)PtMes2·- exhibit virtually no contribution from the coordinated heavy metal to the singly occupied MO (b1) which is mainly centered at the heteroatoms outside the phenanthroline P system. on SciFinder(R)

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