A CRYSTAL THAT HOPS IN PHASE-TRANSITION, THE STRUCTURE OF TRANS,TRANS,ANTI,TRANS,TRANS-PERHYDROPYRENE

Trans,trans,anti,trans,trans-Perhydropyrene, (1,2,3,3ar,4,5,5at,6,7,8,8at,9,10,10ac,10bt,10cc)-hexadecahydropyrene, C16H26, M(r) = 218.38, monoclinic, P2(1)/c, a = 16.782 (7), b = 5.447 (1), c = 16.710 (7) angstrom, beta = 120.00 (3)-degrees, V = 1322.8 (9) angstrom 3, Z = 4, D(x) = 1.097 g cm-3, lambda(CuK-alpha) = 1.54182 angstrom, mu = 4.12 cm-1, F(000) = 488.0, room temperature, R = 0.052 for 1355 observed reflections [greater-than-or-equal-to 3-sigma(I)]. The perhydropyrene molecules are 'planar' in the trans,trans,anti,trans,trans configuration, in which all four cyclohexane rings are in the chair conformation and fused in the trans form. The two halves of crystallographically independent molecules in the asymmetric unit are tilted with respect to each other at a dihedral angle of 53.9-degrees; the crystal structure is of a layer type with hexagonal packing. Upon heating, a phase transformation occurs at 344.5 K which is associated with jumps of the crystals almost 6 cm high. The transformation is probably of the martensitic type with lateral shifts of lattice planes relative to each other.