Room-temperature stable ground-state triplet carbene as models for organic high-spin units with robust π-spin polarization; ESR study and x-ray analysis

We report the first room-temperature stable triplet π-aryl based carbene, 2,2′,4,4′,6,6′,-hexabromodiphenylmethylene 2 in both crystals and fluid solutions. This paper describes ESR detection of 2 in the crystal of the diazo precursor 1 and the molecular and crystal structure of 1 obtained by X-ray diffraction at room temperature. ESR spectroscopy showed that 2 was a triplet molecule in the ground state and survived up to room temperature in the crystal state. The crystal of 1 is monoclinic with cell dimensions, a=9.933Å, b=13.261Å, c=12.743Å, β=91.88° , Z =4 and the space group P2₁/n. The two 2,4,6-bromo-substituted phenyl rings make bent perpendicular conformation with 139° of the bond angle at the diazo methane. Non-bonded contacts shorter than the van der Waals radii were found between the nitrogen and bromine atoms of the nearest neighboring molecules. The correlation between the chemical stability and the molecular structure of 2 is discussed.