Tetrahedral block metal compounds

The pure Sr-doped 123-compound cannot be synthesized at ambient pressure without replacement of some of the other cations. The presence of new structural blocks when substituting square-planar-coordinated Cu atoms of the CuO chain plane, by octahedrally or tetrahedrally coordinated metal atoms opens the possibility to synthesize new superconductors. In the compounds with substitutions that prefer tetrahedral coordinations, M = Co (YSr2CoCu20) [7.57, 7.58], M = Al ((Yo.75Ceo.25)2(Sro.85Yo.i5)2AlCu209) and M = Ga ((Y, Ce) Sr2GaCu207+2n) oxygen-ordered superstructures in the MO plane have been encountered. 

Investigations of cyanides and cyano complexes of Cd and Hg have augmented tremendously since about 1990, after detection of inclusion compounds of Cd(CN)2. A thorough review on transition-metal cyanides especially emphasizes the chemistry of inclusion compounds of both the Hofmann type (frameworks dominated by planar Ni(CN)4 building blocks) and the cyanocad-mate type (frameworks with tetrahedral Cd(CN)4 units).87 The structures of these inclusion compounds, but also of cyanides themselves, often topologically resemble the structures of minerals this aspect ( mineralomimetic chemistry ) is dealt with in a simultaneous survey.88 A more generic review of framework structures, with a section on cyanide inclusion compounds, is also to be mentioned.90... 

Zinti compounds are the compounds formed by the combination of an electropositive metal with a p-block element of intermediate electronegativity. Some of such compounds contain discrete polymeric units such as Ge4 tetrahedral in KGe. In some others we find continuous bonded networks such as Si... 

The building block of each layer of 10 is the spherical icosahedral giant oxidized cluster cage of the Mo72Fe3o type but which now has a reduced metal-oxide-based cluster - the tetrahedral two-electron reduced Keggin [H2PM012040] ion-as nucleus (Figure 8). Like in the layer compound 8, each of the cluster-cluster composites is linked to four others via Fe-O-Fe bonds to form a layer structure. 

As compared to the V/O/PO4, however, the chemistry of V/O/SO4 system remains unexplored. The studies in this area have either been confined to few molecular compounds or concerned with the possible catalytic roles of VO/SO4 compounds in the industrial production of sulfuric acid ". This is despite the recent molecular modeling studies which predicts the potential of the tetrahedral SO4 group as suitable building block for the construction of new metal-sulfate based materials . Since vanadium exhibits rich coordination chemistry bonding to a variety of organic ligands , their incorporation in the... 

Metal-nitrogen distances, as observed in a very large number of crystal structure determinations, are almost the same as those observed for the azole ligands (see Table 2) within experimental error. Comparing pyridine with substituted ligands, it is observed that substituents at position 2 (and 6) next to the donor atom have a dramatic effect upon the stoichiometry and properties of the compounds formed. It appears that a stoichiometry M(Rpy)4(anion)2 with a trans orientation of the anions is not possible, because the methyl group effectively blocks the axial coordination sites. This results in square-planar low-spin compounds for Ni and tetrahedral geometry for some other metals such as Co " and... 

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