Heteronuclear clusters characterization

Various homo- or heteronuclear cluster species which contain both a- and 7r-bonded alkynyl groups have been synthesized and characterized, e.g., [Ag5(C=CPh)6]-,278... 

Rational synthetic routes to heteronuclear clusters are still not as freely available as might be desired. Geolfroy et al. (1,2) have discussed the general synthetic routes to heteronuclear clusters, and these apply equally to Pt-containing clusters. For a detailed discussion on synthetic strategies and on the methods used in characterizing clusters, the interested reader is directed to earlier reviews (1,2). Specific synthetic reactions are discussed under the in-... 

H NMR spectroscopy has been used extensively in the characterization of gold heteronuclear cluster compounds that possess hydride ligands. For example, Fig. 12 illustrates the hydride region of the H NMR spectrum of [Au4Rh(H)2 P(0-i-C3H7)3 2(PPh3)4]+ (155). 

The heteronuclear clusters described previously also conform to this generalization, as Tables XVI and XVII demonstrate. All of the clusters characterized by 12ns + 16 valence electrons adopt toroidal geometries and will readily add one molecule of carbon monoxide to give clusters with a valence electron count of 12ns + 18. The resultant metal cage geometries have been described as either spherical or hemispherical. 

Various homo- and heteronuclear cluster species which contain both a and 7r-bonded aUsynyl groups have been synthesized and characterized, for example [Ag5(C=CPh)e] [Ag3(C=CPh)2(dppm)3]+ [dppm = bis(l,l-diphenylphosphino)methane], [Au2Ag2 (C=CPh)4(PPh3)2] - and [AgeCuvjCsCPhjwj l Compounds with silver(I) bonded side-on to oleflns are rare and are generally very unstable both thermally and chemically. No specific preparative methods have been established. Formation of such adducts has been included in other chapters on structure and bonding. 

Heteronuclear correlation (HETCOR) is an experiment establishing a correlation between the chemical shift of proton and that for another nucleus (i.e. C, P, Nor Si). The experiment relies on the heteronuclear dipolar interactions and uses a CP to transfer magnetization from protons to a rare spin.4,6 We have used 2D HETCOR experiment to characterize support/counter-cation/cluster interaction in the supported mesoporous catalysts.21... 

Structurally Characterized Examples of Heteronuclear Gold Cluster Compounds... 

Single-crystal X-ray crystallography remains the only definitive technique for the structural characterization of heteronuclear gold cluster compounds, although other techniques, in particular Mossbauer, NMR, IR, and fast atom bombardment mass spectroscopies (FABMS), have yielded valuable information, especially concerning the nature of these species in solution. Electron spectroscopy, which has proved to be of great value in the identification of homonuclear gold cluster compounds (210) has received little attention by workers in this area,... 

Fast atom bombardment mass spectroscopy has proved to be most useful when applied to the characterization of heteronuclear gold cluster compounds containing hydride ligands (137,149,155). Characterization is aided by the observation that peaks are invariably present in the spectrum corresponding to ions that contain all of the hydride... 

As is the case for transition metal cluster compounds in general, singlecrystal X-ray diffraction is normally the only technique available for the unambiguous structural characterization of heteronuclear Group IB metal clusters. Tables I, II, and IV-XIV indicate the mixed-metal clusters containing one or more ML (M = Cu, Ag, or Au L = two-electron donor ligand) units which have been studied by X-ray crystallography. Other... 

Another technique that has recently proved to be very useful for facilitating the characterization of heteronuclear Group IB metal cluster compounds is fast atom bombardment (FAB) mass spectrometry. Although the mass spectra of some mixed-metal clusters containing ML units have... 

The term Zintl phase is applied to solids formed between either an alkali- or alkaline-earth metal and a main group p-block element from group 14, 15, or 16 in the periodic table. These phases are characterized by a network of homonuclear or heteronuclear polyatomic clusters (the Zintl ions), which carry a net negative charge, and that are neutralized by cations. Broader definitions of the Zintl phase are sometimes used. Group 13 elements have been included with the Zintl anions and an electropositive rare-earth element or transition element with a filled d shell (e.g. Cu) or empty d shell (e.g. Ti) has replaced the alkali- or alkaline-earth element in some reports. Although the bonding between the Zintl ions and the cations in the Zintl phases is markedly polar, by our earlier definition those compounds formed between the alkali- or alkaline-earth metals with the heavier anions (i.e. Sn, Pb, Bi) can be considered intermetallic phases. 

A.2.2 Nonpolar Binary Intermetallic Phases. Zintl phases are characterized by the presence of markedly heteropolar bonding between the Zintl ions (electronegative polyatomic clusters) and the more electropositive metal atoms. By contrast, the bonding between heteronuclear atoms within other intermetallic compounds is primarily covalent or metallic. A number of different structure types exist for any given... 

Heteronuclear compounds with an Fe-M bond have received much attention in the past decade. Significant progress has been made both in their synthetic methodologies and in the study of their chemical reactivity. There are more than 300 papers that have reported on the chemistry of this class of compounds, and more than 700 structurally characterized mixed-metal compounds that contain iron have appeared since this area was reviewed in COMC (1995). Clearly, this volume of data and information should be best presented in a systematic way, for which a tabulated form is preferable. All of the heterodinuclear species and mixed-metal clusters with known structures are therefore presented in Tables 1-3 respectively. 

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