Halide Cluster Complexes

Both of these elements show a marked tendency to form metal atom cluster compounds in their lower oxidation states. The best known are oxo and halide cluster complexes. 

In the reactions of 10.13a with alkali metal terr-butoxides cage expansion occurs to give the sixteen-atom cluster 10.15, in which two molecules of MO Bu (M = Na, K) are inserted into the dimeric structure. The cluster 10.13a also undergoes transmetallation reactions with coinage metals. For example, the reactions with silver(I) or copper(I) halides produces complexes in which three of the ions are replaced by Ag" or Cu" ions and a molecule of lithium halide is incorporated in the cluster. ... 

Two halide-centered cubane silver cluster complexes, containing discrete units, [Ag8X Se2P(OEt)2 6][PF6], or unidimensional chains, Ag8X[Se2-P(OEt)2]6X ra (X = Br and Cl) have been reported. This is an interesting case where the counter ions dictate the molecular/supramolecular architecture.440... 

Coordination complexes that have metal halide clusters as their central cations represent a unique branch of coordination chemistry. The [M6X12]" cluster... 

Metal carbonyl anions react with main group halides and oxides to yield a number of main-group transition-metal carbonyl complexes in good yields. These complexes serve as starting materials for a number of higher nuclearity cluster complexes. 

A novel method for synthesizing polythiaether macrocycles with Re cluster complex was proposed by Adams and coworkers [185]. This process involves catalysis by the Re complex rather than the stoichiometric displacement of dithiol or dithiolates by organic halides, and first example of a catalytic procedure for synthesis of polythiaether macrocycle using thietanes. The macro-cyclic products formed are shown in Fig. 56. 

Protonation reactions may be simply H+ addition in which the E-M framework of a cluster complex remains essentially unaltered. Where simple protonation is observed, conventional acid-base chemistry is involved and the site of protonation is almost always the electron-rich metal center, though protonation can sometimes be observed at E. Likewise, addition of bases to metal cluster hydrides results in the deprotonation [e.q., Eq. (243)179] Sometimes even halide ions in nonaqueous media are strong enough to deprotonate the metal centers [Eqs. (244)-(246)95 203,373]. Os-... 

Technetium(II) complexes are paramagnetic with the d5 low-spin configuration. A characteristic feature is the considerable number of mixed-valence halide clusters containing Tc in oxidation states of +1.5 to + 3. This area has been reviewed (42). For convenience, all complexes, except those of [Tc2]6+, are treated together here. EPR spectroscopy is particularly useful in both the detection of species in this oxidation state and the study of exchange reactions in solution. The nuclear spin of "Tc (1 = f) results in spectra of 10 lines with superimposed hyperfine splitting. The d5 low-spin system is treated as a d1 system in the hole formalism (40). 

In the kinetic interpretation of ECL data presented above the closest approach of reactants has been assumed. It seems to be fulfilled in the case of organic ECL systems (because of the Coulombic attraction between oppositely charged ions). In contrast, in ECL systems involving identically charged transition-metal complexes, Coulombic repulsion may lead to an increase in the electron transfer distance. The molybdenum(II) halide cluster ion MoeCliJ [197-199] is the one of the best-understood examples. In electrochemical reactions MogCliJ is reversibly reduced or oxidized to stable MosCl and Mo6Cl["4 respectively ... 

A. Organometallic Complexes Halide Complexes and Clusters Complexes with Nitrogen Ligands Phosphine, Arsine, and Related Complexes Complexes with Sulfur Ligands Nitrosyl and Thionitrosyl Complexes Technetium(III)... 

The different homo- and hetero-complexes observed and their thermochemical data are summarized in various review articles by McPhail et al. [424], Schafer [425, 426], 0ye and Gruen [427], Hastie [428, 429], Novikov and Gavryuchenkov [430], Biichler and Berkowitz-Mattuk [268], as well as Bauer and Porter [59]. Gaseous metal halide species is the only subject of these articles. Rules were developed to predict many properties of complexes (see Refs. 426, 428, 430). Brooker and Papatheodorou [431] as well as Papatheodorou [432] give an account of the vibrational properties and spectroscopic studies of the complexes. Theoretical and experimental investigations of alkali halide clusters are reviewed by Martin [433]. 

These considerations, however, cannot exclude the possibility that a vibration of a pyridine-halide-metal (atom or surface) complex is responsible for the debated Raman feature. This would explain the shift of the frequency from that of a metal-halide frequency, the stability to cathodic potentials" (and, perhaps, the relative insensitivity to the metal itself). One should mention in this context that Krasser et reported a band at 240 cm in the Raman spectrum of pyridine-silver cluster complexes, which they associate with a pyridine-Ag mode. 

Reduction of [Mo CIg] and [Mo ClgX ] anions (X = Cl, Br, or I) by certain tertiary phosphines gave complexes of stoicheiometry MOgClgX3(PR3)3, which are formulated to have an ionic structure [MOgCl8(PR3)g] [Mo Clg]X in which the cation is a derivative of the previously unknown [Mo Clg] cluster. The use of photoelectron spectroscopy to determine structures of metal halide clusters has been reviewed. " A detailed study of the force fields for MojXg anions (X = Cr or Br) has indicated that 6 bonds do not play a significant part in the M—M bond strength of molybdenum halides. ... 

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