Mercury transition metal clusters

MERCURY-BRIDGED TRANSITION METAL CLUSTER DERIVATIVES AND THEIR PRECURSOR... 

Mercury-bridged Transition Metal Cluster Derivatives 329... 

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... 

Compared with the transition-metal cluster chemistry, the post-transition element counterpart may appear as a bewildering jungle inhabited by bizarre molecular objects. In Figure 1 a typical transition-metal cluster is compared with two examples from the cluster chemistry of mercury and sulfur. The selection of clusters for Fig. 1 is somewhat biased in order to clearly demonstrate the following points ... 

The first example of a solid compound (Na3Hg2 amalgam) containing doubly cr- and 7T-aromatic transition metal cluster Hg " was discovered by Kuznetsov et al. [27]. Formation of the Hg " cluster was puzzling since mercury has a closed shell electron configuration (6s ), and therefore a neutral Hg4 cluster is expected to be a van der Waals complex. The stability of the Hg " building block can be explained due to the fact that it is isoelectronic to the first all-metal aromatic cluster. 

The reaction of these platinum or palladium clusters with transition metal compounds has also been studied and many cluster derivatives have been prepared for this method, which included reactions with gold,3 02-3306 silver, 302,33 3,3307-3310 copper 3302,3303,3309-3311 Qr mercury com ... 

Mercury(II) forms a series of compounds in which it is bonded to a transition metal to form heteronuclear Hg—M bonds.540,541 The most widely used synthetic routes have been reviewed elsewhere.542-549 Besides heteronuclear bonds M—Hg there are structural elements M—Hg— M, 550 e.g. (31), or cyclic arrangements as in Os3(CO)uHg 3415 or (1/5-MeC5H4)Mn(CO)2Hg 4.416 A trigonal prismatic coordination of mercury has been reported in the green zerovalent mixed metal cluster [Hg Pt(2,6-Me2C6H3NC)fi ]. a... 

The dissociation energies of alkali-metal clusters show variations due to even-odd effects and shell closures. This is not the case for mercury. The dissociation energies and the mass spectra show no trace of similar rapid variations. The dot-dashed line is from the tight-binding calculation of Pastor et a/. - for neutral Hg clusters. It deviates from the experimental result already for n = 3 and shows a much smoother transition. The experiment points to a more abrupt transition between the different regions of binding. 

In summary, ionisation potentials, dissociation and cohesive energies for mercury clusters have been determined. The mass spectrum of negatively charged Hg clusters is reported. The influence of the transition from van der Waals (n < 13), to covalent (30 < n < 70) to metallic bonding (n > 100) is discussed. A cluster is defined to be metallic , if the ionisation potential behaves like that calculated for a metal sphere. The difference between the measured ionisation potential and that expected for a metallic cluster vanishes rather suddenly around n 100 Hg atoms per cluster. Two possible interpretations are discussed, a rapid decrease of the nearest-neighbour distance and/or the analogue of a Mott transition in a finite system. Electronic correlation effects are strong they make the experimentally observed transitions van der Waals/covalent and covalent/metallic more pronounced than calculated in an independent electron theory. 

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