Heterometallic cores

Few gold compounds contain vanadium-carbonyl fragments or dicyclopentadienyl-niobium fragments, respectively, and no additional interactions between discrete heterometalic cores are present in the crystal of any of them. 

Reactions of clusters with mononuclear or dinuclear metal complexes frequently provide a method of expanding the metal core nuclearity under controlled conditions. The majority of medium- and high-nuclearity homometallic clusters has been prepared from lower-nuclearity cluster precursors by thermolyses ("heat-it-and-hope ) reactions. This is less true of the heterometallic clusters in this... 

An extension of this kind of antennae is a first-generation heterometallic den-drimer with appended organic chromophores like pyrenyl units [25,26]. In the tetranuclear species consisting of an Os(II)-based core surrounded by three Ru(II)-based moieties and six pyrenyl units in the periphery, 100% efficient energy transfer is observed to the Os(II) core regardless of the light-absorbing unit. 

There are, of course, metal-containing dendrimers that belong to more than one of the above-mentioned categories. Examples are the heptametallic dendrimer made of a central Fe(Cp)(C6Me6)+ core and coated with 6 ferrocene moieties [ 12], and the heterometallic dendrimers made of an organic core, containing up to 6 Pt(IV)-based organometallic species in the branches, and coated with up to 12 ferrocene units [13]. 

PhN(H))2(tBuO)LiNaK(TMEDA)2]2 406.425 The centrosymmetric structure is composed of a 12-vertex cage in which two Li and two Na cations are four-coordinate in a distorted tetrahedron, while the K cations are six coordinate and octahedral. While Na binds only to N, the Li and K cations bond with 2N/20 and 4N/20, respectively. In a now familiar pattern, the Li cations occupy the core while the structure periphery is comprised of a (K- -N- -Na- N- K- N- -Na- -N) cycle of atoms, though an alternative description is of a (KO)2 ring sandwiched between two heterometallic (LiNNaN) rings. 

Homo- and heterometallic rhenium oxomethoxide clusters with a [M4(/i-0)2(/r-0Me)4] (M = Re, Nb, Ta) planar core have been obtained by anodic oxidation of Re metal in methanol. [Re406(0Me)i2] has been studied crystallographically. The molecule is built up of a planar rectangular tetranuclear [Re4(/u-0)2(/u-0Me)404(0Me)8] unit. The heterometallic members of the family [Re4 xMx06-7(0Me)i2+3 ] (M = Mo, W) have been obtained by interaction of Rc207 with MO(OMe)4 or M(OMe)6 in toluene at reflux. 

The structural chemistry of compounds containing Au-Group 8 metal bonds, and espedally that of dusters, is by far the best represented in the literature in comparison with those of the other transition metals [224]. There are many similarities between the heterometallic duster cores in compounds with Au-Fe, Au-Ru and Au-Os bonds, but also some differences which will be emphasized in the subsequent discussion. 

Two homometallic octanuclear clusters, [FegS CNBu1) ] [37] and [Fe8S8 (PCy 3)61 [37,38], have been isolated (see earlier discussion), as has the related heterometallic cluster [Mo2Fe6S8(PEt3)6(tccat)2] [70], The latter cluster is the first example of an Fe—S edge-linked, reduced MoFe3S4 double-cubane with Mo atoms at the periphery of each cuboid subunit. The reduced double-cubane core is stabilized by triethylphosphane coordinated to the Fe atoms. The utility of such materials as precursors to potential cofactor models, both structural and functional, has yet to be explored. 

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