Two spin-containing fragments connected by a two-electron one-center heteroatom pi spacer. A new open-shell organic molecule with a singlet ground state

摘要

The synthesis of 4,4-iminobis (2,2',2 ",4',4 ",6,6',6 "-octachlorotriphenylmethyl) diradical 3, a stable organic magnetic molecule consisting of two spin-containing fragments linked by a nitrogen atom, is reported. Electron paramagnetic resonance (EPR) analysis in methyltetrahydrofuran solution (similar to 10(-3) M) at low temperatures showed a typical fine structure (g(xx) = 2.0042; g(yy) = 2.0048; g(zz) = 2.0027) of Delta m(s) = +/- 1 transition (D/he = 0.0071 cm(-1); E/hc = 0.0006 cm(-1)) as well as a broad (Delta H-pp = 7.5 G) and weak signal of Delta m(s) = +/-2 transition (g = 4.124), due to an asymmetric and excited triplet state corresponding to an intramolecular spin-spin interaction which diminishes with decreasing temperature. It also showed a pair of small peaks, that might be associated with a weaker dipole-dipole interaction which diminishes with increasing temperature, emerging at both sides of a central and single peak due to a doublet state resonance corresponding to 2,2',2 ",4',4 ",6,6',6 "-octachloro-4-{3,5-dichloro-4-[bis(2,4,6-trichlorophenyl)methylene]cycloh exa-2,5-dienylideneamino}triphenylmethyl radical 4, obtained by smooth oxidation of 3. From magnetic susceptibility measurements of the sample in the solid, a linear four-spin model was applied to establish that the singlet is the ground state of the molecule and that two triplets (J(intra) = -286 +/- 30 K, J(inter)' = -160 +/- 50 K) were the low-lying excited states. Organic solutions of 3 in air slowly oxidize to give 4, a much more persistent monoradical which is also obtained by a smooth oxidation of 3 with AgNO3 in CHCl3. Cyclic voltammograms for the reduction of 3 and 3 in dimethylformamide (DMF) with tetra-n-butylammonium perchlorate exhibited three consecutive redox couples with standard potentials of -0.23, -0.58 and -0.74 V vs. SCE, indicating a reasonable stability of anions 3(.-) and 3(2-) in DMF solution. [References: 35]