The structural characterisation of telluraphthalic anhydride, selenaphthalic anhydride and of 2-selenaphthalide

The characterisation, by single crystal X-ray methods, of three heterocycli c organoselenium and -tellurium compounds is reported. Tellura phthalic anh ydride (1), C8H4O2Te, and selenaphthalic anhydride (2), C8H4O2Se, are both monoclinic and crystallise in space group P2(1)/n. 2-Selenophthalide (3), C 8H6OSe, is also monoclinic, space group P2(1)/c. The Te(Se)-C(sp(2)) bond l engths in 1, 2, and 3, averaging at 2.161(6) Angstrom (Te) and 1.945(1) Ang strom (Se) are longer than observed normally (2.116 and 1.893 Angstrom, res pectively). No evidence of electron delocalisation in the heterocyclic ring s of 1 and 2 is noted; however, a short C(8)-C(7) bond and a relatively lon g C(8) = O bond in 3 indicates some degree of delocalisation in that case. (C) 1999 Elsevier Science S.A. All rights reserved.