A FLUORINE BOMB CALORIMETRIC DETERMINATION OF THE STANDARD MOLAR ENTHALPY OF FORMATION OF SILICON DISULFIDE SIS2(CR) AT THE TEMPERATURE 298.15 K - ENTHALPIES OF DISSOCIATION OF SI-S BONDS

A synthesis of high-purity silicon disulfide SiS2 is described, and th e F.t.-Raman spectrum of the solid is reported for the first time. The standard massic energy of reaction of SiS2(cr) with fluorine was meas ured in a bomb calorimeter. The combustion reaction was shown to proce ed as follows: SiS2(cr) + 8F(2)(g) = SiF4(g) + 2SF(6)(g). The derived standard molar enthalpy of formation is: Delta(f)H(m)(o)(SiS2,cr, 298. 15 K) = -(254.6 +/- 2.9) kJ . mol(-1). This value differs significantl y From those determined by solution-reaction calorimetry, but is in fa ir agreement with results obtained by means of third-law treatments of high-temperature equilibria. The ratio of molar enthalpies of dissoci ation of the ''first'' and ''second'' bonds in SiS2(g), k = D-m(o)(S-S iS)/D-m(o)(SiS) = (0.57 +/- 0.03), is similar to ks reported previousl y for SiO2 and SiSe2. (C) 1997 Academic Press Limited.