Département de chimie moléculaire

Reactions of the unsym. phenol ligand 2-(bis(2-pyridylmethyl)aminomethyl)-6-((2-pyridylmethyl)(benzyl)aminomethyl)-4-methylphenol with Mn(OAc)2·4H2O or Mn(H2O)6(ClO4)2 in the presence of NaOBz affords the dimanganese(II) complexes (1-MeOH), [Mn2(L)(OAc)2(MeOH)](ClO4), and (2-H2O), [Mn2(L)(OBz)2(H2O)](ClO4), resp. However, reaction of the ligand with hydrated Mn(III) acetate furnishes the mixed-valent deriv. (3-H2O), [Mn2(L)(OAc)2(H2O)](ClO4)2. The three complexes were characterized by x-ray crystallog. 1(MeOH) crystallizes in the monoclinic system, space group P21/c, with a 10.9215(6), b 20.2318(12), c 19.1354(12) {\AA}, $\alpha$ 90., $\beta$ 97.5310(10), $\gamma$ 90.°, and Z = 4. 2(H2O) crystallizes in the monoclinic system, space group P21/n, with a 10.9215(6), b 20.2318(12), c 19.1354(12) {\AA}, $\alpha$ 90., $\beta$ 97.5310(10), $\gamma$ 90.°, and Z = 4. 3(H2O) crystallizes in the monoclinic system, space group P21/c, with a 11.144(6), b 18.737(10), c 23.949(13) {\AA}, $\alpha$ 90., $\beta$ 95.910(10), $\gamma$ 90.°, and Z = 4. Magnetic measurements revealed that the three compds. exhibit very similar magnetic exchange interactions -J = 4.3(3) cm-1. They were used to establish tentative magneto-structural correlations which show that for the dimanganese(II) complexes -J decreases when the Mn-Ophenoxo distance increases as expected from orbital overlap considerations. For the dimanganese(II,III) complexes, crystallog. results show that the MnII-Ophenoxo and MnIII-Ophenoxo bond lengths are inversely correlated. An interesting magneto-structural correlation is found between -J and the difference between these bond lengths, $δ$Mn-O = dMnII-O - dMnIII-O: the smaller this difference, the larger -J. Electrochem. studies show that the mixed-valence state is favored in 1-3 by ∼100 mV with respect to analogous complexes of sym. ligands, owing to the asymmetry of the electron d. as found in the analogous diiron complexes. [on SciFinder(R)]