The molecular structure of thiophthen from X-ray crysal analysis

The molecular structure of thiophthen, C6H4S2, has been determined by X-ray analysis, using Fourier three-dimensional syntheses and differential syntheses. Corrections have been made for `termination of the series' errors, which were found to be important in this structure. The bond lengths in the centro-symmegrical molecule are C1—C2 = 1.36 A., C2—C3 = 1.41 A., C3—C3′ = 1.36 A., C1—S = 1.72 A., C3′—S = 1.74 A. A statistical analysis of the accuracy of these values has been attempted from information given by the differential syntheses. The results are discussed in relation to molecular orbital calculations on thiophen and to similar preliminary calculations on thiophthen itself. While the general agreement is good, there appear to be significant discrepancies between theory and experiment in the lengths of the C—S bonds and of the central C—C bond of the molecule. It is suggested that only for the latter must reconciliation necessarily be sought in a refinement of the theoretical treatment; while the C—S discrepancy may be accounted for in the same way, it is also possible that it will be partially or wholly removed by revision of the C—S bond-order/length relationship, knowledge of which is at present inadequate.