Group 12 Dihalides: Structural Predilections from Gases to Solids

Abstract

Connections between the structures of Group 12 dihalides in their vapor and crystal phases are sought and discussed. The molecular structures of all monomers and dimers (MX(2): M=Zn, Cd, Hg and X=F, Cl, Br, I) were calculated at the density functional B3PW91 and MP2 computational levels. All the monomers are linear, with the mercury dihalide molecules having shorter bonds than their cadmium analogues; the ZnX(2) and CdX(2) structures are similar. The shorter Hg-X distances are traced back to relativistic effects. For the dimers, many possible geometrical arrangements were considered. The zinc and cadmium dihalide dimers have the usual D(2h)-symmetry geometry, whereas the mercury dihalide dimers are loosely-bound units with C(2h) symmetry. The origins of this C(2h) structure are discussed from different points of view, including frontier orbital interactions. The crystals of Group 12 dihalides span a wide range of structure types, from three-dimensional extended solids to molecular crystals. There is an obvious connection between the structures and characteristics of monomers, their dimers, and the crystals they form. The similarities as well as startling differences from the Group 2 dihalides are analyzed.

A solid-state 199Hg NMR study of mercury halides

“…The mercurous halides [37,38] and the mercuric halides [14,36,39] have been the subject of theoretical studies. For such studies, the importance of including relativistic effects on the electronic structure of mercury compounds has been known for some time [36,39,40].…”

“…For such studies, the importance of including relativistic effects on the electronic structure of mercury compounds has been known for some time [36,39,40]. The fact that electrons may be moving at appreciable fractions of the speed of light requires that relativistically invariant calculations such as the zeroth-order regular approximation (ZORA) with density functional theory (DFT) [25,[41][42][43] be used to calculate the 199 Hg NMR chemical shielding.…”

“…HgF 2 has a CaF 2 (fluorite) structure [8,39] with a coordination number of 8, very different from the other mercuric halides. The mercury atom is located at the center of a cubic cell with eight fluorine atoms at the corners.…”

“…For the fluorite structure of HgF 2 , Donald et al [39] argue that this structural preference, at least to some degree, results from the difference of the ratio of the metal cation radius to that of the fluoride ion, as compared to the other halide ions. They note that the radius of the Hg 2+ cation (~114 pm) is relatively close to that of the Ca 2+ cation (~112 pm).…”

Predicting the Relative Stability of Simple versus ansa‐Sandwich Systems Across Groups: Structure, Bonding, and (In)Stability in Tris(sandwich)benzene Complexes

“…Our computational results, including all the optimized geometries, vibrational analyses, and the assessments of the bond orders in the molecules have been obtained with the B3PW91 [38] density functional method; in other studies in our group, [39] this method has afforded optimized geometries in better agreement with experiment than B3LYP. For Groups 6, 7, and 8 metals we employed the energy-consistent small-core MDF effective-core potentials (ECPs), without the spin-orbit potential, but retaining the treatment of scalar-relativistic effects (for 10, 28, and 60 core electrons for Periods 4, 5, and 6, respectively), [40] and their associated MDF basis sets.…”