MOLECULAR AND IONIC SUBLIMATION OF NEODYMIUM TRIBROMIDE POLYCRYSTALS
1187
orates the hypothesis that the sublimation of ionic clusters lanthanide series are linearly independent. The thermo-
dynamic functions of Nd2Br–7 were estimated by an
takes place via a “diffusionless” mechanism [2].
The enthalpy and activation energy of sublima-
additivity method using an empirical correction, as was
tion of the NdBr–4 ion were derived from the slope of done in [29]. The thermodynamic functions of the
LuBr3 molecule and the LuBr–4 ion were taken from [2];
those of crystalline NdBr3, from [21]. The following
enthalpies of formation (∆fH0(298.15 K), kJ mol–1) were
the log logIT1/2 = f(1/í) curve. At the mean experimental
temperature, ∆sH°(NdBr–4 , 879 K) = 290.0 13.6 kJ mol–1
and Es(NdBr–4 , 848 K) = 286.5 13.5 kJ mol–1. Within
the indicated errors, these values are equal to the
enthalpy of sublimation (279.6 kJ mol–1) and the activa-
tion energy of sublimation (292.1 kJ mol–1) of the
NdBr3 monomer.
also used: LuBr3, –538 15 [2]; LuBr–4 , –1085 23 [2];
NdBr3, cr, –864.0 3.0 [25].
ACKNOWLEDGMENTS
The enthalpies of formation of ions. The enthalpy
This study was supported by the Russian Founda-
tion for Basic Research, project no. 06-03-32496.
of formation of the NdBr–4 ion was determined by a
procedure based on investigation of gas-phase ion–
molecule exchange reactions in binary or more com-
plex systems [27]. To make use of this procedure, we stud-
ied the LuBr3–NdBr3 system and measured the equilib-
rium constant of the following reaction (Table 3):
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(5)
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RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 54 No. 8 2009