Sesquiselenides

O Hare, P.A.G., Lewis, B.M., Susman, S. and Volin, K.J. (1990) Standard molar enthalpies of formation and transition at the temperature 298.15 K and other thermodynamic properties of the crystalline and vitreous forms of arsenic sesquiselenide (As2S3). Dissociation enthalpies of As-Se bonds. Journal of Chemical Thermodynamics, 22, 1191-206. 

Cobalt Subselenide, Co2Se.—On reducing either the sesquiselenide or tricobalt tetraselenide in a current of hydrogen at bright red heat the subselenide is obtained as a brilliant silver-white mass. 

Cobalt Sesquiselenide, Co2Se3, is formed by passing hydrogen selenide over cobalt chloride at dull red heat. It is a grey amorphous mass. 

Iridium Sesquiselenide, Ir2Se3, is obtained as a black precipitate by the action of hydrogen selenide upon a hot solution of iridium trichloride.5... 

Uranium Sesquiselenide, UaSCg, is formed when a current of hydrogen mixed with a small proportion of selenium vapour is passed rapidly over the double sodium uranium chloride, Na2U4Clg, at 1000° C. ... 

The sesquisulfides and sesquiselenides, are tetramers, (RSnXi.s)4, with adamantane-like structures.5 23> 24... 

ZHD/MAL] Zhdanov, V. M., Mal tsev, A. K., Low-temperature heat capacity, enthalpy, and entropy of crystalline and vitreous arsenic sesquiselenide and of crystalline arsenic sesquitelluride, Russ. J. Phys. Chem., 42, (1968), 1078-1080. Cited on pages 190, 191. 

LAG/SUS] Lagnier, R., Suski, W., Wojakowski, A., Heat capacity of the uranium sesquiselenide, Phys. Status Solidi, A29, (1975), K51-K54. Cited on page 388. 

BAR/P1A] Bardi, G., Piacente, V., Scardala, P., Vaporization enthalpy of indium sesquiselenide from its vapor pressure. High Temp. Sci., 25, (1988), 175-185. Cited on page 244, 568. 

The same procedure is used for 063864 and Prg8e4. However, Nd yields only Ndi eg.s. The other rare earths do not form poly-selenides. The sesquiselenides of these elements are best prepared by treating the rare earth chlorides with Hg8e ... 

Pressure-temperature-induced transition to the cubic, deficient ThjP -type structure for rare earth sesquisulfides and sesquiselenides, determined on quenched samples by Eatough et al. (1969) and Eatough and Hall (1970). The selenide phases were prepared from stoichiometric mixtures of the components. 

The sesquisulfide Cm2S3 forms a defect body-centered cubic phase of the Th3P4 type with lattice parameter 8.452(5) A [47]. The sesquiselenide was obtained by thermal dissociation of CmSe2 at 620°C, again yielding a Th3P4-type phase, with cell parameter a = 8.788 A [47]. Unlike gadolinium or plutonium, no other sesquiselenide forms were observed, even after thermal treatment at various temperatures. 

Samarium monoselenide can be prepared from Sm2Se3 at 1700°C in a vacuum, Guittard, Benacerraf [12]. Thermal decomposition of the sesquiselenides M2Se3, M = La to Nd and Gd, or the diselenides at 1800°C and 10"" Torr results in a mixture of MSe and M3Se4 [12], Obolonchik, Mikhlina [13]. Small amounts of MSe, M = La and Ce, in a mixture with other selenides are obtained from M2Se3 and a calculated amount of metal M at 1700°C in 1 h [12]. The dull black YbSe sample prepared from Yb2Se3 in an H2 stream at 1250°C for 8 h contained some oxide, Senff, Klemm [14]. 

High temperature-high pressure synthesis has been used to make the Th3P4 polymorphs of heavier rare earth sesquiselenides from stoichiometric amounts of the powdered elements. Possibly, they are nonstoichiometric, Se-deficient products. The following compounds were obtained at 1800°C ... 

The cation anion ratio in the SC2S3 type sesquiselenides varies over a wider range than in the corresponding tellurides. The distortion of the SC2S3 structure increases in the M sequence 8c[Pg.38]

Fig. 3. Theoretical densities Dcaic of rare earth sesquiselenides as a function of ionic radius rM-...

Sesquiselenides have lower a than the monoselenides, probably due to the more covalent bond character in M2S03 and higher harmonic lattice vibrations ... 

Melting points for the Th3P4 type sesquiselenides estimated with use of crystal chemical data, see Kuz micheva et al. [9]. 

The higher values for Sm2Se3 as compared to 0q values in the M series La to Nd are due to partial divalency, Dudniketal. [2]. A universal value 0o 25O Kfor M2Se3 compounds is given in Takeshita et al. [8]. Debye temperatures for the Th3P4 type sesquiselenides estimated with use of crystal chemical data, see Kuz micheva et al. [9]. 

Sesquiselenides with M = Pr, Nd, Sm decompose in moistair after a long time with liberation of H2Se, Obolonchik, Mikhlina [3, 7]. Slow liberation of red Se from material not kept in a dry glove box to avoid reaction with atmospheric moisture was observed by Guittard et al. [1]. Signs of decomposition had earlier been found after a few days, Klemm, Koczy [2]. 

The sesquiselenides of the Ce subgroup are insoluble in hot and cold water, Klemm, Koczy [2], Obolonchik, Mikhlina [3,4,7]. The sesquiselenides dissolve and give off H2Se when reacted with 25% H2O2 at 20°C [4]. 

Sesquiselenides (M = Sc, Ho, Er, Tm, Yb) react with rare earth hydrides above 1350°C to give monoselenides M2Se3+MH2- 3MSe +H2, Skripka et al. [8], Obolonchik et al. [10, 18]. The reaction with the oxides in vacuum at 1350°C gives M202Se, Guittard et al. [1], Benacerraf etal. [5]. 

Organic acids and ethanol decompose the sesquiselenides with liberation of H2Se [4]. References ... 

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