SYNTHESIS, STRUCTURE AND SOLID-STATE POLYMERIZATION OF DIMETHYL(PROPYNOATO)THALLIUM

The structure of acetatodimethylthallium 2 has been used as a model in an attempt to predict and 'engineer' a phase of dimethyl(propynoato)thallium 3 which would be reactive in the solid state. Upon irradiation with X-rays or Co-60 gamma-rays, 3 is indeed converted to the corresponding deep-brown polypropynoate. The crystal structure of 3 contains, as expected, an infinite set of short contacts (3.454 Angstrom) between acetylene moieties; the presence of such a chain is a requirement for a propynoate material to be sensitive to ionizing radiation. However, the crystal structures of 2 and 3 are quite different owing to subtle changes in C-H...O hydrogen bonding. Crystals of 3, (CH3)(2)Tl(O2CC=CH), belong to the orthorhombic system, space group Pnma, a = 7.316(4), b = 11.268(6), c = 9.033(5) Angstrom; Z = 4. Full-matrix least-squares refinement of positional and displacement parameters for all nonhydrogen atoms, using 338 data for which \F-0\>3.92 sigma(\F-0\), led to R=0.059 and R(w) = 0.068.