Metal cluster late transition metals

L. Wang and D. D. Johnson, Density Functional Study of Structural Trends for Late Transition Metal 13 Atom Clusters, Rhys. Rev. B 75 (2007), 235405. 

It is possible to use ancillary ligands in addition to phosphonic acids in building up nanosized cluster compounds of late transition metal ions. Thus, the reaction of CuCl2 with tert-butylphosphonic acid in the presence of 3,5-dimethylpyrazole affords a dodecanuclear copper phosphonate with an interesting cage structure,3 Similarly, large vanadium phosphonate clusters with up to 18 vanadium atoms have been assembled from phosphonic acids.35... 

The potential that HNCC offer is beginning to be realized. It is clear that they have properties and exhibit reaction patterns that differ markedly from their mononuclear counterparts and even low-nuclearity clusters. It is also apparent that their reactivity patterns may be rationalized in simplistic terms and thereby extended to other systems. However, much work remains to be done, particularly in designed synthesis and studies of reaction mechanisms. The ability of these clusters to combine with important small substrates such as CO and Hj need also to be explored in much more detail. The study of the reactivity of large mixed-metal systems, which, as expected, exhibit enhanced and modified reactivities, equally requires more detailed investigation. In fact it would be useful to have available HNCC, which contain early and late transition metal elements, in order to combine both Lewis basic and Lewis... 

Thiolato and S-based ligands have often been also used to bridge two metals with the formation of heterobimetallic complexes. The synthesis and reactivity of cubane-type sulfido clusters containing titanium-late transition metals have been reviewed.1776,1777... 

When the same tin/iridium stiochiometry is employed, but a small amount of THF is added to the solvent, the major product is now an air-sensitive purple cluster, again with an Ir3Su2 framework. This material has no bridging carbonyl stretches, is diamagnetic, and shows a H NMR peak in solution at d-9.61 a region typical of late transition metal hydrides. The structure of this species, [Ir3(//-SnR2)2(CO)sH], is shown in Fig. 16. 

In other complexes, N2 is bound both end-on and side-on. In some end-on/side-on complexes, each metal plays its customary role, with an alkali metal bound side-on and a late transition metal bound end-on." " In one very unusual compound, though, lithium atoms are at the ends of N2 and nickel coordinates to the side. In some homometallic clusters, N2 is bound end-on to some metals and side-on to others. One of the best-characterized examples of end-on/side-on binding is in [(NPN)Ta]2(N2) (2), " in which the unsymmetric binding of N2 activates it toward... 

Fig. 11 Schematic depicting an inverse micelle sol-gel method developed for the preparation of mesoporous late transition metal oxides, (a) Transition metal oxo-clusters, (b) P123 surfactant, (c) 1-butanol, which stabilises the micelles and increases the solubility of the surfactant and (d) nitrate ions. Reproduced with permission from ref. 45. Copyright 2013 Nature Publishing Group. ...

The apparent completely different nature of the bonding between clusters like [M06O12] and [Os3(CO),2] makes the application of similar concepts or of a unifying view quite difficult. However, it is certainly possible to draw some general conclusions about the electronic character of the late transition metal clusters, that is, for clusters of metal atoms in low oxidation states. These systems also represent the largest fraction of the dusters reported so far. 

The lack of late transition-metal halide clusters and the poor bonding which results when they are formed can be easily rationalized. In binary metal halide clusters the metal atoms are in a high oxidation state. The valence orbital contraction in these high oxidation state metals is much greater for the later transition metals than it is for the early ones. The diminished radical extension of the valence shell inhibits metal-metal bonding. 

Kirsch and Harris [176] calculated Ni(OOl) surface reconstructions induced by C, N, and O adsorption and suggested that C and N atoms prefer the nearly coplanar sites with the top Ni surface, which induce the clock reconstruction of the surface. However, O atoms prefer sites slightly above the Ni(lOO) surface plane and have little effect on the overall surface structure. The local environments of the C, N, and O atoms on these surfaces are similar to their environments in a series of late transition metal carbonyl clusters, suggesting that some of the same electronic factors may play a role in favouring different structures. Results of the calculations suggest that adsorbates occupy coplanar sites on Ni(lOO) surface disrupt the Ni-Ni bonding within the surface layer and bonds between the surface and second layers. 

---