✍ Scribed by P.A.G. O'Hare; Andrzej Żywociński; L.A. Curtiss
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This review deals with the critical assessment of the thermodynamic properties of several germanium selenides: GeSe(cr), GeSe(g), GeSe2(cr), GeSe2(g), and Ge2Se2(g). In the absence of experimental information, the structures, internuclear distances, and vibrational wavenumbers were calculated for GeSe2(g) and Ge2Se2(g) by molecular orbital methods. The triatomic GeSue2(g) is linear. The tetratomic selenide has a butterfly-shaped structure, with alternating Ge and Se atoms, akin to Ge2S2(g), but the interplanar angle, close to 0.78•p, is smaller than in the sulfur-containing analog. Statistical mechanical methods were used to calculate the conventional molar thermodynamic functions {C°p,m(T ), D T 0 S°m, D T T' H°m, and F°m(T )} of GeSe, GeSe2, and Ge2Se2 in the ideal gas state at a pressure p°=101.325 kPa with T '=298.15 K. Heat capacities of solid GeSe and GeSe2 reported in the literature were re-evaluated from T 4 0 to the melting temperatures. The enthalpy of sublimation DsubH°m(GeSe,298.15 K) is selected as (172.721.0) kJ•mol -1 on the basis of a third-law evaluation of published vapor pressure measurements. A similar treatment yielded DrH°m(298.15 K)=(295.821.0) kJ•mol -1 for the reaction: GeSe2(cr)=GeSe(g)+( 12 )Se2(g). For dissociation of Ge-Se bonds, enthalpies D°m, and mean enthalpies D°m , were calculated to be: D°m(GeSe)=(480.621.7) kJ•mol -1 at T 4 0; D°m (GeSe2) = (36429) kJ•mol -1 , and D°m (Ge2Se2) = (27022) kJ•mol -1 , both at T=298.15 K. The trend in values of enthalpies of dissociation parallels the nominal bond orders.
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