摘要:

The application of polymetallic complexes to photochemical energy conversion is an active area of research. The use of tridentate complexes within this context has been less well explored than the highly studied trisbidentate structural motif. Recent interest has expanded to explore the class of tridentate bridged complexes that incorporate RuIIand OsIIchromophores. These systems hold promise in that they give rise to polymetallic systems that are stereochemically defined. This is important in the construction of molecular devices that utilize energy or electron transfer as it will allow control of donor—acceptor distance and orientation. This article describes some of the recent research in the construction and study of polyazine-based, tridentate-bridged complexes containing Ru11and Os11chromophores.

ISSN:0260-3594    

DOI:10.1080/02603599908012007

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Although solid state metal oxides are of both fundamental and practical interest, the designed synthesis of such materials remains an elusive goal. However, valuable synthetic guidelines may be derived from a consideration of the plethora of Nature's remarkable materials which contain composites of molecules or microstructures in which inorganic components coexist with organic components. The presence of organic subunits can profoundly influence the crystallization of the inorganic microstructure, offering a powerful tool for the design of novel materials. In the specific case of molybdenum oxide phases, metal-organoamine molecules, fragments, an even polymeric coordination complex cations may be exploited in the self-assembly of complex hierarchical materials.

ISSN:0260-3594    

DOI:10.1080/02603599908012008

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

The chemistry of Sm2+in solid oxide environment is reviewed and explored by a systematic search for crystal lattices stabilizing Sm2+at particular reaction conditions. It is demonstrated that SrB4C7is representing an unique lattice stabilizing Sm2+even when crystals are prepared in air. However, when exchanging Sr by e.g. Ca, Ba, Cd, Pb, only Sm3+doping could be traced. Sm2+in lattices free of nuclear spins is of interest to hyperfine optical hole burning. In this respect we have prepared single crystals of SrSO4doped predominantly by Sm2+. In summary, we can say that the stability of Sm2+in an oxide environment is strongly depending on local effects of coordination and a reduction mechanism not revealed so far. In particular it remains unclear, why Sm2+can be included into SrB4O7crystals under oxidizing conditions, whereas in the rapidly cooled melt no Sm2+could be traced.

ISSN:0260-3594    

DOI:10.1080/02603599908012009

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Pentadienyl ligands have been found to possess many unique and potentially useful characteristics, including the ability to adopt a wide variety of η1, η3, and η5bonding modes, a propensity for bonding to metals in low oxidation states, a tendency toward forming sterically crowded complexes, and the ability to engage in a wide variety of coupling reactions, even while being more strongly bound to a metal center than the ubiquitous cyclopentadienyl ligand. The combination of these properties has led to a rich body of chemistry for these ligands, and the promise that much more remains to be gained.

ISSN:0260-3594    

DOI:10.1080/02603599908012010

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Discoveries on B12models made since 1989 are assessed in the light of the advances in structural and spectroscopic methodologies. Further studies emanating in part from these advances have confirmed, often definitively, previously identified principles describing the properties of the classic simple models (cobaloximes and iminocobaloximes) and have established some new principles defining the properties of the axial Co-C and Co-N bonds; the latter are clearly relevant to enzymatic processes. Some new simple models have been proposed and studied in relation to the classic ones and to the more complicated natural cobalamins. In several cases, the influence of the steric and electronic factors have been established, sometimes in semi-quantitative terms, also with the help of studies on the rhodium analogues of cobaloximes. New spectroscopic techniques have been introduced, which have been found useful in the study of the natural cobalamins. Recent structural analyses of the binding site in some B12-based enzymes have shown that the B12cofactors bind in the base-off form, with displacement of the benzimidazole residue from cobalt and coordination of a histidine residue of the protein chain. Such observations have stimulated new experiments aimed at defining the mechanism of the Co-C homolytic cleavage in isomerases and mutases or at testing the recently proposed mechanism for the Co-C heterolytic cleavage in methionine synthase. As a consequence, the information now available on models and on cobalamins (e.g., on the nature of the Co-S bond) is much broader in scope, and these advances have prompted this new analysis of models. The experimental aspects have advanced much more quickly than our theoretical understanding, and hence further calculations, possibly based on more sophisticated approaches, are clearly required.

ISSN:0260-3594    

DOI:10.1080/02603599908012011

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor