Studies of a polymerizable crystal : I. - structure of monomer pts (bis-p-toluenesulphonate of 2,4-hexadiyne 1,6-diol) by neutron diffraction at 120 and 221 k

Abstract

The crystal and molecular structures of monomer pTS (bis-p-toluenesulphonate of 2,4-hexadiyne 1,6-diol) have been determined by neutron diffraction at 120 K and 221 K. The low-temperature structure is monoclinic P21/e with Z = 4, and a = 14.745(7) Å, b = 5.086(2) Å, c = 25.738(12) Å, β = 91.71(5) deg., V = 1929 Å3 at 120 K. The high-temperature structure is also monoclinic P21/c but with Z = 2 and a = 14.630(20) Å, b = 5.133(2) Å, c = 14.845(15) Å, β = 118.55(7) deg., V = 979 Å 3 at 221 K. This corresponds to a room temperature b parameter of 5.178 Å. The four molecules in the low-temperature unit cell are unstrained and all lie at centres of symmetry. They belong to two families (sites) with different geometries and different environments. Particular diacetylene groups on the two sites have slightly different orientation and intermolecular contacts. Toluenesulphonate side groups have few atom-atom intermolecular contacts and exhibit libration of large amplitude at 120 K, leaving room for the contraction along b brought about by polymerization. A « conventional » analysis of the 221 K structure (i.e. without positional disorder) shows very large libration of the side groups. It could be analysed by assuming disorder, each side group occupying either of two configurations which are very similar to the two low-temperature site configurations. However, the barrier height between the two configurations, deduced from TLS analysis of thermal motions, is very low. Except for this, the overall molecular geometries and intermolecular contacts are very similar to those found at 120 K. pTS monomer and poly-pTS- polymer have similar structure both at low- and high-temperatures. The relevance of the structure to reactivity and various electronic properties is briefly discussed