Multimetallic systems

On the one hand, this mechanistic study represents the culmination of many preceding studies. On the other hand, this, together with several other recent developments, represents a new generation of organozirconium chemistry characterized by (i) Zr catalysis, (ii) bimetallic and multimetallic systems, in which bi- and multimetallic interplay is significant, and (iii) significant roles of various 0-bond metatheses. 

Further studies on this system will include IR-SEC experiments under an atmosphere of CO to verify its catalytic activity for CO reduction and to aid in formulating a mechanism for the reaction. Other multimetallic systems used as CO reduction catalysts such as mthenium-, iridium-, and cobalt-based complexes, or metal clusters used as models in the active sites of biological systems, many of which have complex redox behavior can also be investigated using the IR-SEC technique. 

Acyclic Schiff base derivatives represent a resourceful class of compartmental ligands which are prepared by self-condensation of appropriate formyl and amine precursors. The condensation reaction is simple and generally leads to the desired product in high yield. Literature data on Lnm mono- and bimetallic complexes, as well as on 4f-d transition metal bimetallic entities with these derivatives are abundant and have been reviewed recently (Vigato and Tamburini, 2004). Extension to multimetallic systems and to complexes with 5f elements... 

A great advantage of X-ray spectroscopy over other experimental probes of multimetallic systems is that the X-ray process takes place in the immediate locality of an atom, so that the electronic structure of each atomic constituent can be studied separately. 

Multimetallic cymantrenes such as (36) and (37) have recently been reported. An especially interesting multimetallic system is (38), in which two cymantrene units are linked by a pyrazolate bridge. Electrochemical measurements show that the two metal centers in (38) interact... 

Past efforts in developing coal liquefaction catalysts have focused on alumina-supported systems and, except for exploratory studies, little attention has been given to systematic development of novel formulations. A particularly promising approach to the development of new catalysts specifically designed lor coal liquefaction processes lies in the formulation of multicomponent systems that, in comparison to work on single or bimetallic systems, are essentially unexplored. Use of multimetallic systems offers the possibility of multifunctional catalysts that are needed to perform the many different reactions encountered in coal processing. Because of its versatility for the preparation of multimetallic catalysts, the HTO system is an excellent candidate for further development. 

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. 

Edge-coalesced icosahedra eleven-coordinate compounds, 99 repulsion energy coefficients, 33, 34 Effective atomic number concept, 16 Effective bond length ratios non-bonding electron pairs, 37 Effective Eight-coordinate compounds stereochemistry, 86-94 Electrochemistry, 475-477 aqueous solution, 479-490 multimetallic systems, 485 non-aqueous solutions, 493 Electrodes... 

Cooperative action of multimetallic systems in promotion of certain types of organic reactions... 

When the activation of metal cations is done by their chelation with polydentate carboxylic acids the reasons for cation segregation in multimetallic systems are incomplete chelation, so that part of the metal precipitates as nitrates or hydroxides during the dehydration (condensation) step, and selective precipitation of some metal carboxylates occurs at corresponding pH... 

Ara, L Berenguer, J. R. Eguizabal, E. Fomies, J., and Lalinde, E. (2001). Formation of an Unsymmetrical Pt-Ir Tetraalkynyl Complex and Investigation into Subsequent Construction of Multimetallic Systems. Organometallics, 20,2686-2696. 

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