CRYSTAL-STRUCTURES OF A TETRAOXY SPIROCYCLIC SELENURANE AND TELLURANE- LONE-PAIR EFFECTS (REPRINTED FROM INORG CHEM, VOL 20, PG 3071, 1981)

The crystal structures of the tetraoxy spirocyclic selenurane (C6H12O2 )(2)Se (3) and corresponding tellurane (C6H12O2)(2)Te (4) have been de termined by single-crystal X-ray diffraction analysis. Both compounds crystallize in the monoclinic space group C2/c with Z = 4 and with the central atom on a crystallographic twofold axis. For 3, a = 10.442 (6 ) Angstrom, b = 10.545 (5) Angstrom, c = 13.910 (3) Angstrom, and beta = 110.27 (3)degrees. For 4, a = 19.108 (7) Angstrom, b = 10.469 (4) A ngstrom, c = 7.705 (2) Angstrom, and beta = 97.83 degrees. Data for bo th compounds were collected on an Enraf-Nonius CAD4 diffractometer out to a maximum 2 theta(MoK alpha) of 50 degrees. Full-matrix least-squa res refinement led to R = 0.042 and R(w) = 0.055 for 3 and R = 0.034 a nd R(w) = 0.042 for 4. Both exist in a trigonal-bipyramidal structure distorted in compliance with the presence of an equatorially positione d lone electron pair. In the Te compound intermolecular Te-O contacts indicate a degree of polymerization making the Te atoms pseudo six-coo rdinated. No such contact is observed in the Se moiety.