Chemistry, commentary and community: Discussion of “The NaDyBr4 complex: its molecular structure and thermodynamic properties” by Varga and Hargittai

Abstract

The molecular geometries, relative stabilities, binding energies, and dissociation energies of NaDyBr 4 and its molecular ion are discussed. Both the bidentate and tridentate isomers are stable for the neutral species, while only the bidentate form is stable for NaDyBr 4 + .Keywords NaDyBr 4 . NaDyBr 4 + . Complex halides . Multiple isomers . Relative stabilities In a recent paper two of us (ZV and MH) presented a computational study of the structure and energetics of the gas phase NaDyBr 4 complex [1]. Multiple isomers were discussed wherein 1, 2, 3, and 4 bromines bridged the two metal centers-the discussion was dominated by bi-and tridentate species. It was shown that these bi-and tridentate forms have comparable binding (in terms of enthalpy) between the NaBr and DyBr 3 fragments while the monodentate species has one, and the tetradentate three imaginary frequencies and they are not stable. At the highest level of calculation employed for the two (bidentate and tridentate) isomers the enthalpy of reaction (1) NaDyBr 4 → NaBr + DyBr 3(1) was found to be 246.7 and 230.6 kJ/mol for the tri-and bidentate isomers, respectively. A Boltzmann weighted average of 233.1 kJ/mol-corresponding to the abundances of the isomers at 1000 K-was in comfortable agreement with 240.6 ± 12.6, 247.7 ± 10.5, and 242.7 ± 5.6 kJ/mol offered in the experimental literature, depending on the mode of analysis of the results [2, 3]. Entropically, for these two isomers the value of S • of reaction (1) was shown to equal 151.3 J/mol-K and 133.0 J/mol-K, respectively, with a weighted average of 135.8 J/mol-K; the experimental literature offers the comparable value of 146.5 ± 6.8 J/mol-K [3]. Study [1] reproduced the adiabatic ionization potential; the bi-and tridentate isomers had values of 8.9 and 9.0 eV while refs. [2] and [3] reported measured values of 9.3 and 8.9 eV showing good agreement. It is apparent that quantum chemical calculations can reliably describe the energetics of NaDyBr 4 .It is encouraging that the tri-and bidentate isomers are of comparable stability. As such, one may view NaDyBr 4 as a complex of DyBr 4 − and Na + (after all, the charge on the Dy is ca. 2.4, near the classical ionic value of + 3, and on Na and Br nearly + 1 and − 1; 0.94 and − 0.84, respectively). Accordingly, with its nearly tetrahedral local environment for the dysprosium, we recognize the near isotropicity of the DyBr 4 − ion and make use of the multiple thermochemical conclusions drawn for NH 4 + because of its tetrahedral shape [4]. Among these conclusions is the suggested independence of location of the counterion and so we are not surprised that the tri-and bidentate isomers of NaDyBr 4 have nearly the same energies and enthalpies. Sharing such a comparison constitutes one issue for inclusion in this current commentary and community contribution to Structural Chemistry.However, it is worthwhile to emphasize that the above is valid only at high temperatures where these species actually exist in the vapor phase. According to the highest level Springer

Magdolna Hargittai’s inorganic structures

“…The operation of metal halide lamps is an example in which lanthanide trihalides are involved. Magdi and her co-workers carried out computations on a series of complexes of dysprosium trihalides with alkali halides, MDyX 4 [19][20][21]. Figure 7a shows the PES of the NaDyBr 4 complex.…”

Interplay of thermochemistry and Structural Chemistry, the journal (volume 17, 2006) and the discipline

“…The relative energies of these isomers are temperature dependent. Additional thermochemical context for this species was discussed in the paper [133].…”

Interplay of thermochemistry and Structural Chemistry, the journal (volume 18, 2007) and the discipline

“…The first article of the new column, by Liebman et al [124], discusses the molecular structure and thermodynamic properties of NaDyBr 4 complex. A computational study of the structure and energetics of the isomers of gas phase NaDyBr 4 and related ions such as DyBr 4 -was earlier presented by Varga and Hargittai [125].…”