Chlorine nuclear quadrupole resonance in mercury chlorides and complex chlorides

Abstract

Chlorine nuclear quadrupole resonance frequencies are reported for solid compounds of known structure containing linear molecules HgCl₂ and Hg₂Cl₂, approximately trigonal HgCl₃-, and a variety of distorted octahedral forms including NH₄HgCl₃, CsHgCl₃, and K₂HgCl₄,H₂O. Compounds of unknown structure of the type (cation⁺)HgCl₃, (cation⁺)₂HgCl₄, (cation⁺)Hg₂Cl₅, (cation⁺)₂Hg₉Cl₂₀, and (cation⁺)₄HgCl₆ have also been studied. There are clear correlations between observed n.q.r. frequencies and Hg-Cl infrared stretching frequencies and bond distances. These correlations show the dependence of the degree of covalent bonding in the Hg-Cl bond with distance. The n.q.r. data confirm that many of the complex chlorides of mercury are built up by the joining of octahedral HgCl₆ units, distorted in such a way as to preserve to varying extents the identity of the HgCl₂ molecule.     Predictions of the structures are made for some complex chlorides of unknown structure, and the role of bridging in building up the compounds is discussed in terms of observed n.q.r. data for bridging chlorines.