Structural studies in the lepidopterene system

Abstract

.A new, metastable phase of lepidopterene, (5,6,11,12-tetrahydro-4b,12[1',2']:6,10b[1",2"]-dibenzenochrysene) (1), has been obtained from methylene chloride solution, exhibiting a luminescence which differs from that of the stable form, having an absorption maximum at 580 nm rather than 560 nm. Single crystal X-ray diffraction determination of the structure of the new phase shows it to be orthorhombic, Pbcn, a 36.75(3), b 7.229(7), c 44.85(3) Ǻ, Z 24, the structure being refined to a residual of 0.065 for 2413 independent 'observed' reflections. Despite the relatively low precision of the determination, it is evident that in the metastable form, the gross molecular disposition is severely distorted. The crystal structure of dimethyllepidopterene (2) has also been determined, and refined by least squares to a residual of 0.041 for 632 'observed' reflections. Crystals are mono- clinic, P2₁/c, with a 9.607(4), b 11.564(7), c 10.576(6) Ǻ, β 107.72(4), Z 2; the molecules are centrosymmetric. Tetrachlorolepidopterene (31, formed by the dimerization of 1,5-dichloro-9-anthrylmethyl, yields two crystalline forms from xylene and methylene chloride solutions which differ in their crystal exciplex luminescence, showing emission maxima at 590 and 575 nrn respectively. Single- crystal X-ray structure determination confirms that the two crystalline forms, α- and β-, are polymorphs of the same centrosymmetric molecular species. For the α-form, crystals are triclinic, P1 , a 15.374(6), b 9.858(4), c 8.000(4) Ǻ, α 83.98(4), β 83.73(3), γ 71.53(3)°, Z 2, 2138 independent 'observed' reflections being refined to a residual of 0.037; the unit cell contains two independent centrosymmetric molecules. For the β-form, crystals are monoclinic, C2/c, a 11.03(2), b 13.67(2), c 16.32(3) Ǻ, β 1 1 1.13(12)°, Z 4; the residual for 1554 independent reflections was 0.053.