Energetics and Stabilities of the IIB/VIA‐Compounds at High‐Temperature Equilibrium Conditions

Abstract

Equilibrium vaporization behaviour of twelve IIB/VIA‐compounds of the type MeX was studied by means of high‐temperature mass spectrometry. In all cases except HgTe the existence of stable MeX(g)‐molecules was established. Bond energies D0(MeXgas) were determined by the thermodynamic third‐law method and range as follows: ZnO(g) (280.1 kJ/mol)/ZnS(g) (224.8)/ZnSe(g) (170.8)/ZnTe(g) (117.7)/CdO(g) (230.3)/CdS(g) (208.5)/CdSe(g) (127.7)/CdTe(g) (100.1)/HgO(g) (221.1)/HgS(g) (217.3)/HgSe(g) (144.5). ‐ Comparison of the third‐law bond energies with existing experimental data, upper limits of D0 given by other authors, and semi‐empirical estimates shows basic agreement. Data for the heat of dissociative vaporization ΔH0R, the heat of atomization ΔH0at, the parameter , and the chemical stabilities of the IIB/VIA‐systems are also presented.

Revision of the Dissociation Energies of Mercury Chalcogenides—Unusual Types of Mercury Bonding

“…It is the primary objective of the present paper to carry out relativistically corrected high-level ab initio calculations for the monomeric HgE and dimeric (HgE) 2 (E = O, S, Se) species and to study their relative stabilities and bonding features. If the dimeric mercury chalcogenides happen to be considerably more stable than the monomeric species, the discrepancy between measured [7] and calculated dissociation energies for the monomeric species [9,10] can be explained as resulting from dimerization (or even polymerization) of monomeric species in the gas phase. This would be the basis for answering questions that emerge in connection with points 1) to 4) mentioned above.…”

“…Originally, gaseous HgO was tentatively identified by infrared spectroscopy in rare gas matrices under nonstationary vaporization conditions. [6] Later, mass spectrometric measurements suggested [7] a dissociation energy D 0 of 53 AE 8 kcal mol À1 for HgO, which implied that the reaction of gaseous elemental mercury with bromine oxide should be nearly thermoneutral [D 0 (BrO) = 55.2 AE 0.4 kcal mol À1 as obtained from heats of formation at 0 K [8] ]. However, recent high-level ab initio calculations predict for the dissociation energy D e of HgO a 50 kcal mol À1 lower value of just 4 kcal mol À1 .…”

“…[7] The question is only whether HgO or a species (HgO) n with n = 2, 3… rather n = 1 was found because for all values of n the same charge/mass ratio will be found. For example, judging from the electronegativities of elemental mercury and oxygen, the gas-phase mercury monoxide should be a polar molecule with a large dipole moment.…”

“…This of course would have serious implications for the understanding of the chemistry of mercury, [12,13] and even the chemistry of the other group-12 compounds, namely Zn and Cd: 1) Besides HgO, also HgS and HgSe were investigated and dissociation energies D 0 of 52 AE 5 and 35 AE 7 kcal mol À1 , [7] respectively, were measured for these compounds. Any inconsistency between theory and experiment found for HgO should also apply to the other mercury chalcogenides HgE.…”

Bonding in Mercury Molecules Described by the Normalized Elimination of the Small Component and Coupled Cluster Theory

“…[59] Filatov and Cremer [19] have suggested that the mass-spectrometric investigation of HgE molecules [65] were flawed by the fact that mixtures of HgE dimers and trimers were measured. Such an error is unlikely under normal conditions, because the natural distribution of Hg and E isotopes should lead to m/e signals clearly different for monomer, dimer, and trimer.…”