Transition metal-cluster ions

The red tetrathiomolybdate ion appears to be a principal participant in the biological Cu—Mo antagonism and is reactive toward other transition-metal ions to produce a wide variety of heteronuclear transition-metal sulfide complexes and clusters (13,14). For example, tetrathiomolybdate serves as a bidentate ligand for Co, forming Co(MoSTetrathiomolybdates and their mixed metal complexes are of interest as catalyst precursors for the hydrotreating of petroleum (qv) (15) and the hydroHquefaction of coal (see Coal conversion processes) (16). The intermediate forms MoOS Mo02S 2> MoO S have also been prepared (17). 

Perspectives for fabrication of improved oxygen electrodes at a low cost have been offered by non-noble, transition metal catalysts, although their intrinsic catalytic activity and stability are lower in comparison with those of Pt and Pt-alloys. The vast majority of these materials comprise (1) macrocyclic metal transition complexes of the N4-type having Fe or Co as the central metal ion, i.e., porphyrins, phthalocyanines, and tetraazaannulenes [6-8] (2) transition metal carbides, nitrides, and oxides (e.g., FeCjc, TaOjcNy, MnOx) and (3) transition metal chalcogenide cluster compounds based on Chevrel phases, and Ru-based cluster/amorphous systems that contain chalcogen elements, mostly selenium. 

The electron paramagnetic resonance spectrum of transition metal ions has been widely used to interpret the state of these ions in systems of catalytic interest. Major emphasis has been placed on supported chromia because of its catalytic importance in low-pressure ethylene polymerization and other commercial reactions. Earlier work on chromia-alumina catalysts has been reviewed by Poole and Maclver 146). On alumina it appears that the chromium is present in three general forms the S phase, which is isolated Cr3+ on the surface or in the lattice the 0 phase, which is clusters of Cr3+ and the y phase, which is isolated Cr5+ on the surface. The S and 0... 

Abstract Amino acids are the basic building blocks in the chemistry of life. This chapter describes the controllable assembly, structures and properties of lathanide(III)-transition metal-amino acid clusters developed recently by our group. The effects on the assembly of several factors of influence, such as presence of a secondary ligand, lanthanides, crystallization conditions, the ratio of metal ions to amino acids, and transition metal ions have been expounded. The dynamic balance of metalloligands and the substitution of weak coordination bonds account for the occurrence of diverse structures in this series of compounds. 

The versatile binding modes of the Cu2+ ion with coordination number from four to six due to Jahn-Teller distortion is one of the important reasons for the diverse structures of the Cu-Ln amino acid complexes. In contrast, other transition metal ions prefer the octahedral mode. For the divalent ions Co2+, Ni2+, and Zn2+, only two distinct structures were observed one is a heptanuclear octahedral [LnM6] cluster compound, and the other is also heptanuclear but with a trigonal-prismatic structure. 

These and many similar examples resulted in a highly successful general picture of transition-metal ions M coordinated by closed-shell ligands L (anionic or neutral) to form complex cluster ions [ML ]9 in solution. The characteristic coordination shell of each M corresponds to a specific number of sites, with idealized geometry that dictates the possible number of distinct [M(Li) (L2)m. .. ]q structural isomers. Each cluster ion is subject to equilibria with other cluster ions or dissociated ligands in solution,... 

Mixed clusters NH3/H20 (139-141), NH3/MeOH (61), and NH3/Me2CO (142) have been reacted with bare metal ions and in general the transition metal ions preferred coordination to ammonia whereas the non-transition metal ions such as Mg+ and Al+ were nonselective, showing some similarity to condensed-phase systems. 

The deposition of mass and charge selected ions onto surfaces is underway but is in its infancy. How do the ions survive the collision with a surface This question has a myriad of answers depending on many variables and will have a future in investigative studies. A soft landing is now a possibility (280) and allows the potential spectroscopic investigation of trapped ions. So far no transition metal ions have been examined using this method but it is only a matter of time. Soft landings via inert gas matrices also have potential in the surface deposition of mass selected clusters. 

Besides the applications of the electrophilicity index mentioned in the review article [40], following recent applications and developments have been observed, including relationship between basicity and nucleophilicity [64], 3D-quantitative structure activity analysis [65], Quantitative Structure-Toxicity Relationship (QSTR) [66], redox potential [67,68], Woodward-Hoffmann rules [69], Michael-type reactions [70], Sn2 reactions [71], multiphilic descriptions [72], etc. Molecular systems include silylenes [73], heterocyclohexanones [74], pyrido-di-indoles [65], bipyridine [75], aromatic and heterocyclic sulfonamides [76], substituted nitrenes and phosphi-nidenes [77], first-row transition metal ions [67], triruthenium ring core structures [78], benzhydryl derivatives [79], multivalent superatoms [80], nitrobenzodifuroxan [70], dialkylpyridinium ions [81], dioxins [82], arsenosugars and thioarsenicals [83], dynamic properties of clusters and nanostructures [84], porphyrin compounds [85-87], and so on. 

Figure 5.1. Structures, oxidation states and spin states of crystallographically defined Fe-S clusters. Complete cysteinyl ligand (as shown) is most common, although a limited number of examples are known in which histidine, serine, and aspartate residues can act as cluster ligands. The spin states denoted by a question mark have yet to be determined, and the [FesSJ cluster has been observed only as a fragment in heterometaUic [MFejSJ clusters in which M is a divalent transition metal ion.

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