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)
A. Klein et al., 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), Perkin transactions. 2, (12), 1995, pp. 2121-2126
In contrast to the anion radicals of 1,10-phenanthroline (phen) or its
4,7-dimethyl derivative (dmphen) with their B-2(1) ground state, the
3,4,7,8-tetramethyl derivative tmphen(.-) has a (2)A(2) ground state a
s evident from EPR/ENDOR measurements; The small eta spin population a
t the potentially metal-coordinating nitrogen centres in the (2)A(2) s
pecies as opposed to the B-2(1) State causes distinct spectroscopic ef
fects in corresponding diorganoplatinum(II) complexes. The neutral com
pound (phen)PtMes(2), Mes = mesityl, has been structurally characteriz
ed as a square planar Pt-II complex with tightly protected axial sites
: monoclinic, space group P2(1)/c, Z = 4, a = 9.378(1), b = 15.791(2),
c = 16.581(1) Angstrom, beta = 103.18(1)degrees. All complexes ((NN)-
N-Lambda)PtMes(2), (NN)-N-Lambda = bpy (2,2'-bipyridine), phen, tmphen
, dppz (dipyrido[3,2-a :2',3'-c]phenazine) and pdo (1,10-phenanthrolin
e-5,6-dione) are oxidized to EPR-silent platinum(In) species and reduc
ed to anion radical complexes. The latter clearly contain Pt-II and he
terocyclic anion radical ligands; however, they exhibit a trichotomous
EPR behaviour. Whereas the radical complex [(phen)PtMes(2)](.-) shows
a rather low g(iso)-value of 1.983 and distinct anistropy in frozen s
olution like the analogous complex of bpy(.-), the formally related [(
tmphen)PtMes(2)](.-) has an isotropic g-factor (2.0030) much closer to
the free-electron value and a distinctly smaller g anisotropy. The ph
enanthroline-derived radical complexes [(pdo)PtMes(2)](.-) and [(dppz)
Pt-Mes(2)](.-) exhibit virtually no contribution from the coordinated
heavy metal to the singly occupied MO (b,) which is mainly centred at
the heteroatoms outside the phenanthroline pi system.