Département de chimie moléculaire

The pincer ligand H3L3N, {\{}bis(2-amino-3,5-di-tert-butylphenyl)amine{\}}, was chelated to NiII, PdII, and PtII. Square-planar complexes of stoichiometry 2:1 (ligand/metal) formed, wherein the ligand coordinates in a bidentate fashion. By x-ray diffraction each ligand mol. coordinates in its diimino-semiquinone radical form in the neutral NiII, PdII, and PtII complexes (1, 2, and 3, resp.). The resulting systems are singlet diradical species, with a predicted J value in the range -1062 to -1764 cm-1. These diradicals display an intense LLCT transition involving the diimino-semiquinone moieties: 860, 852, and 760 nm for 1,2, and 3, resp. Complex 1, 2, and 3 exhibit reversible oxidn. waves in their CV curves. Cations 1+, 2+, and 3+ are (S = 1/2) systems with g values close to 2. The increase in the intensity of the resonance in the order 1+ {\textless} 2+, 3+ is consistent with the easy comproportionation of 1+. X-ray diffraction anal. discloses that 3+ is a mixed-valent radical mononuclear complex. An intense IVCT is obsd. at low energy (1536, 1656, and 1256 nm for 1+, 2+, and 3+, resp.), confirming that this classification applies to all the cations. Dications 12+, 22+, and 32+ are closed-shell bis(diiminobenzoquinone) species. The crystal structure of 32+ shows that this complex exhibits the shortest mean C-N bond lengths within the series. [on SciFinder(R)]