Homometallic systems

Homometallic systems (i.e. (U02f"" only) with a single linker type. 

Homometallic systems with multiple linker molecules. 

Polymeric supports with R3N+ functional groups were used to attach the anionic cluster [H3RuOs3(CO)j2] . The resulting catalyst was active in the isomerization and hydroformylation of 1-hexene. Its activity was greater than that of corresponding homometallic systems, suggesting a synergistic enhancement. 

Porphyrazines have also been used to prepare metal-metal bonded dimers with ruthenium and osmium, specifically homometallic dimers comprised of two metallic octaethylporphyrazine and heterometallic dimers comprised of one metallic oc-taethylporhyrazine ligand and one metallic octaethylporphyrin ligand have been reported (189-191). The major bonding interactions that occur in these systems are directly between the two metal centers. 

Special 1D systems, chains made of rings, are fluorides with Jarlite or usovite structures (Section 3.2.10). Homometallic or bimetallic chains with various combinations of spins (or nonmagnetic metals) allow the study of ID antiferromagnets, ID ferrimagnets, or linear trimers. ... 

Multidentate oxygen ligands such as the symmetric tetrake-tone (H2L) give an asymmetric complex, [MnsEg], which has been reported as the first asymmetric homometallic helicate formed from a symmetric ligand. " A wide variety of compounds have been studied with the /3-diketonate monoanions such as acetylacetonate (acac) and hexafiuoroacetylacetonate (hfacac) that have been used as ligands in many polymeric systems. "... 

The generally rigid, extended nature of metal polyynes is also evident in their tendency to form lyotropic liquid crystalline phases " " (see also Chapter 12.05 on the topic of organometallic mesogens). Homometallic polymers, as well as mixed metal systems, that contain Pt, Ni, and Pd, have all been shown to exhibit liquid... 

Information on the hydrolysis of mixed-metal alkoxides is even scarcer than for the homometallic. Partial hydrolysis of [LiNb(OEt)6]< leads to the dimeric heterometallic alkoxide [LiNbO(OEt)4(EtOH)]2, in which both the stoichiometry between the two metals and their coordination numbers are retained [93]. On the other hand, the partial hydrolysis of solutions of methoxyethoxides of Ba and Ti (1 1 molar ratio) offers Ba4Tii30i8(0C2H40Me)24 (30% yield). Its structure corresponds to a tetrahedron of BaOs units surimposed on a Ti06(Ti03)i2 core this Tii3042 core is related to that of the aluminum salt [A1i304(0H)24(H20)]2+ [83]. The important modification of the stoichiometry between the two metals illustrates the complexity of the sol-gel chemistry of multimetallic systems and shows that important structural rearrangements can occur. 

The ability of tetrachalcogenometallates [ME4]" (M = V, Nb, = 3 M = Mo, W, n = 2 M = Re, n= 1) to act as multidentate ligands to a variety of transition metals has been well documented. " As a result of this coordinative versatility, these complexes have been widely implemented in the synthesis of homometallic and heterometallic metal chalcogenide clusters with intact or altered [ME4] - units. In particular, the synthesis of ternary polynuclear M-Fe-E and M-Cu(Ag)-E complexes has received much attention, due to their relevance to biological systems as well as interesting catalytic and physical properties. 

Although, as already highlighted, the oxalate ion has allowed the construction of magnetic homo- and heterometallic two- and three-dimensional networks, a few examples of homometallic one-dimensional systems of formula (M(//-ox)(L) ) (L=nitrogen donor or water) are known. Most of these are copper(II) systems whose magnetie studies reveal the occurrence of moderate to weak antiferromagnetic and even ferromagnetie intrachain coup-... 

The expression unusual has been deliberately been left open ended or ill defined since the effect will almost certainly differ between systems having different phenomenological bases for cooperativity or synergism. Nevertheless, a rather useful working definition might be a rate or selectivity dependence which cannot be explained as a strictly additive effect of the metal(s) used. Having said that, the homometallic and heterobimetallic catalytic binuclear elimination reactions (CBERs) which are the focus of this chapter have very well-defined rate dependences which can be traced back to the topology of the reaction mechanisms. 

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