The Crystal Structure of 1,2,3,4-Tetrachlorobenzo[g]sesquifulvalene

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Abstract
The molecular structure of 1,2,3,4-tetrachlorobenzo[g]sesquifulvalene has been ascertained by X-ray crystal analysis. The crystal of this substance is monoclinic, with four molecules in a unit cell of dimensions: a=21.31, b=16.88, c=3.83 Å, and β=93.3°, the space group being P21/a. The crystal structure was determined by the Harker-Kasper inequality and the Sayer’s method. The atomic coordinates and the anisotropic temperature factors of each atom were refined by the block-diagonal-matrix least-squares method. The average length of the C–Cl bonds is 1.705 Å, a value which is in good agreement with those of several chlorobenzenes. In the sesquifulvalene skeleton, longer and shorter bonds are disposed as may be expected from the conventional chemical formula. The average length of the longer bonds is 1.461 Å, while that of the shorter ones is 1.354 Å. The mean C–C bond length in the benzene ring is 1.413 Å. The whole molecule is not on a plane, although the component ring systems are nearly planar. The five-membered ring and the seven-membered ring twist to each other by an angle of about 31° around the bond connecting these two rings. This might be due to the repulsion forces between chlorine and hydrogen atoms which approach each other closely. The plane of the seven-membered ring makes an angle of about 5° with that of the six-membered ring.