Mercury cluster anion

Fig. 10. Photoelectron spectra of mercury cluster anions. The right arrows indicate the bottom of the 6p band and the left ones the top of the 6s band. The difference between the two values corresponds to the s-p band gap. (Adapted from Ref. 24.)...

It is known from a variety of crystal structure determinations that the typical interatomic distances d(Hg-Hg) in cationic mercury clusters are significantly smaller ( 250 pm) than in neutral ( 330 pm) and anionic ones ( 300 pm). In a first approximation this is due to a preferred covalent Waals bonding in the neutral (weak) and a preferred Op bonding (medium) in the anionic forms. 

Tab. 2.4-1. Summary of alkali metal (M) amalgams containing anionic" mercury clusters, extended mercury partial structures and/or high coordination number polyhedra.

Fig. 2.4-2. A comparison between (a) cationic and (b) small anionic mercury clusters in alkali and alkaline earth amalgams (distances in pm).

Up till now anionic mercury clusters have only existed as clearly separable structural units in alloys obtained by highly exothermic reactions between electropositive metals (preferably alkali and alkaline earth metals) and mercury. There is, however, weak evidence that some of the clusters might exist as intermediate species in liquid ammonia [13]. Cationic mercury clusters on the other hand are exclusively synthesized and crystallized by solvent reactions. Figure 2.4-2 gives an overview of the shapes of small monomeric and oligomeric anionic mercury clusters found in alkali and alkaline earth amalgams in comparison with a selection of cationic clusters. For isolated single mercury anions and extended network structures of mercury see Section 2.4.2.4. 

There are three important routes to the formation of the mercury-transition metal bond (a) displacement of halogen or pseudohalogen from mercury(II) salts with carbonyl metallate anions (b) reaction of a halo-phenylmercury compound with a transition metal hydride and (c) oxidative addition of a mercury halide to neutral zero valent metals.1 We report here the syntheses of three compounds containing three-centre, two-electron, mercury-ruthenium bonds utilizing trinuclear cluster anions and mercury(II) halides.2-4... 

Au 8M](N03)2 [43]. The structure of [ (Ph3P)Au 8Pt(Hg)](N03)2 14 was determined and the cation was found to be similar [Au-Hg 2.979(5)-3.079(5) A] to that observed in cluster 12, one of the capping Hg atoms being removed (Figure 4.6d). In compounds 12-14 the mercury atoms also interact with the central metal atom (Pd or Pt) while, in contrast to compounds 10 and 11, the capping Hg atoms have no close contacts with N03- anions. 

Another area of major interest in the field is that of mixed metal cluster systems. Hieber very early in the study of metal carbonyl chemistry was able to prepare mercury complexes of the type Fe(CO)4(HgCl)2. The related gold ° compounds were prepared in the 1960s by reaction of phosphine gold halides with carbonyl anions. 

Finally, the stereodynamics of two mercury-containing metal clusters have been reported. The mercury-bridged osmium cluster [ (ju-H)(/i3-S) (C0)90s3 2(/i4-Hg)] exhibits variable-temperature NMR spectra which are attributed to movements of both fi-Hg and /i-H moieties at comparable rates. Mercury halides form adamantane-like anions with chalcogen bridges. The resulting structures [( i-ER)6(HgX)4] (E = S, Se, Te X = C1, Br, I) have been examined in solution by Se, Te, and Hg NMR spectroscopy. The species tend to dissociate in solution. Pyramidal inversions at Se and Te atoms are slow on the NMR time scale at reduced temperatures, but tend to become rapid at ambient temperatures. ... 

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