THERMALLY INDUCED SOLID-STATE Z-E ISOMERIZATION IN BI(CYCLOPENTENYLIDENE) COMPOUNDS - X-RAY CRYSTAL-STRUCTURE OF (Z)-2,2'-DIOXO-3,3',4,4',5ALPHA,5'BETA-HEXAPHENYL-1,1'-BI(CYCLOPENTENYLIDENE)

The crystal and molecular structure of the title compound has been determined; it crystallises as a methanol solvate in the space group P2 1/n with a = 11.647(2), b = 18.583(2), c = 16.113(2) Å, β = 92.11(1)° and Z = 4. The structure has been solved by direct methods and refined to a final R value of 0.090. The molecular structure is different from that proposed earlier on the basis of spectral data. The central bond connecting the two five-membered rings displays pure double-bond character due to lack of conjugation. This is responsible for the thermal stability of the compound and the relatively high temperature for the isomerisation. One of the two five-membered rings assumes an envelope conformation and the other a half-chair. The solvent methanol molecule is disordered.