Chemistry. 2015 Nov 16;21(47):16848-58. doi: 10.1002/chem.201502477. Epub 2015 Oct 20.

The HgF2 Ionic Switch: A Triumph of Electrostatics against Relativistic Odds.

Chemistry (Weinheim an der Bergstrasse, Germany)

Kelling J Donald, William J Kretz, Oluwarotimi Omorodion

PMID: 26481313 DOI: 10.1002/chem.201502477

Abstract

A remarkable transition in the chemical bonding in (HgF2)n clusters as a function of n is identified and characterized. HgF2 is a fascinating material. Certain significant consequences of relativistic effects on the structure of the HgF2 molecule, dimer, and trimer disappear in the extended solid. Relativistic effects in Hg ensure that HgX2 molecules (X≡F, Cl, Br, and I) are linear, rigid, and form weakly bound dimers and trimers held together by weak electrostatic and van der Waals-type forces (unlike ZnX2 and CdX2 systems in which the intermonomer contacts are strong polar covalent bonds). For HgF2, the location and nature of an apparent transition from weak interactions in the smallest (HgF2)n clusters to ionic bonding in the (fluorite) HgF2 extended solid has remained a mystery. Computational evidence obtained at the M06-2X, B97D3, and MP2 levels of theory and reported herein indicate that polar covalent bonding in (HgF2)n begins as early as n=5. For n=2 through to n=13, the transition or switch from weak (primarily dipole-dipole-type) intermonomer interactions to a preference for polar covalent bonding occurs within the range 5

© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Keywords: bonding; clusters; electrostatic interactions; halides; relativistic effects

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• Journal Article