Structure and γ-ray-induced solid-state polymerization of sodium propynoate:: Influence of bilayer formation on solid-state reactivity

Sodium propynoate, Na(O2CC=CH) 1, was synthesized from propynoic acid and sodium hydroside in methanol solution. Irradiation of solid 1 with Co-60 gamma-rays (654 kGy dose) leads to an amorphous dark-colored acetylenic polymer in high yield. An X-ray structure determination of compound 1 shows that the sodium ion is five-coordinate, with a square-pyramidal geometry. The five-coordinate local moiety is part of an unusual two-dimensional polymer in the crystal be plane. Crystal packing of the two-dimensional, solid-state polymers leads to a bilayer motif, and the relatively short metal-metal distance of 3.575 Angstrom promotes close packing of the organic tails with parallel acetylene moieties and a very short -C=C-...-C=C- contact of 3.29 Angstrom along the crystallographic b direction. Crystal data for 1: orthorhombic, space group Pna2(1), a = 19.837(6), b = 3.575(1), and c = 5.232(1) Angstrom; V = 371.0 Angstrom(3); Z = 4; R = 0.0262; R-w = 0.0327 for 427 data for which I > 1.96 sigma(I). (C) 2000 Academic Press.