Polymetallic chains

The solid-state strnctnres of the homoanionic magnesium enolates 30 and 31 and heteroanionic enolate 33 have been determined by X-ray crystallography, establishing as a common motif a polymetallic chain of fonr members for 30 and 32 or three members for 31, with the anionic ligands in each case bridging the different metals together (equations 52-55). 

The longest polymetallic chain known to date for any combination of metals is the nine-atom cluster (Ph3GeCd)(Ph3Ge)(i75-C5H5)Ni]2Cd... 

Trinuclear derivatives of Zn, Cd, and Hg readily undergo insertion of Ni, Pd, and Pt into the metal-metal bond to form a variety of polymetallic chains with loss of PPh3, e.g. ... 

Figure 8. G r) for the platinum blue [Pt2(NH3)4(//-HP04)2] . Different types of atom are labeled with numbers in the diagram of the model - 1, 2, 3, 4 indicate the Pt atoms of the polymetallic chain, 5 is the oxygen atom, 6 the ammonia ligand, and 7 the phosphorus atom.

Thus, in the next examples, we comment on supramolecular entities, including linear chains, two-dimensional sheets, and even three-dimensional networks. From them, perhaps the most common structural arrangement is that in which the metals form extended linear systems, usually built from mononuclear units, dinuclear, using polydentate donor ligands and polymetallic units. It is worth mentioning that in this part and also in the following we consider only structures built by gold-heterometal interactions, not bonds thus formal clusters will not be considered. 

The particle size can easily be precisely adjusted by the chain length of the alkyl radical and the applied concentration of the trialkyl-aluminum compound. If mixtures of low-valency carbonyl compounds of different metals are used, polymetallic alloy particles form. For example With a molar Co Al ratio of about 10 1, the thermolysis of Co carbonyl yields a Co particle size of 10 nm in the presence of AljCgHiyls, 6nm in the presence of A1(C2H5)3 and 3.5 nm in the presence of A1(CH3)3. If in the case of Al(CgHi7)3, the molar Co A1 ratio in the batch is changed from 12 1 to 0.5 1, the particle size decreases from 10 to 5.4nm. 

Metal-metal interactions can be consolidated by additional steric interactions to ensure the linearity of infinite metal-metal chains. For example, Pt-Pt scaffolding with sufficiently bulky ligands interact to occupy the space around the polymetallic core. Additional weak interactions can be suspected when heteroatoms are in close contact with C-H groups, as is the case with the cyano /erfto-butyl ligand in Figure 13. However, the effects of steric bulk seem predominant. The Pt-Pt interactions in the wires obtained by this approach are responsible for the luminescent character of the wires and the emission can be modulated by exposme to acetonitrile that introduces small distortions along the Pt metallic chain. 

As represented in Scheme 27.11, monometallic species A and bimetallics Bl, B2 would be prone to propagate the polymerization in a l,4-/rans manner, whereas B3 would be a dormant form. Cl, C2, and C3 trimetalUc species result from the reaction with an additional BEM molecule among them, C2 and C3 may preferentially lead to 3,4-polyisoprene, while other possible dormant forms are not represented. The more BEM is present in the mixture, the more 3,4-polymer is formed by displacement of equilibria toward polymetallic species. Note that the growth of several polymer chains per catalyst metal is not considered here. 

Bridging groups other than cyanide can also be used to link Ru(bpy)2 centers to other metal complexes. A series of bridging groups of differing chain length and conjugation have been used to synthesize a variety of new polymetallic complexes... 

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