Five-coordinate species shape

Theoretical studies have also been made on nickelacyclopentane. In practice the product of decomposition of such a compound, [L Ni], depends on its coordination number, being, respectively, butene, cyclobutane, and ethene for (n + 2) = 3, 4, and 5. The theoretical studies show that for planar four- and three-coordinate systems viz. cis-[L2Ni] and [LNi]), the reductive elimination of cyclobutane is symmetry allowed, while the production of ethene is not. The reverse is true for tetrahedral [L2Ni]. Five-coordinate species, [LsNi], can give either cyclobutane or cyclobutane and ethene depending on their shape. 

The Bp ligand is the simplest of all the heteroscorpionate ligands. It is basically bidentate, forming the typical boat-shaped H2B( x-pz)2M ring, in which the pseudoaxial B-H may form an agostic bond with the metal.4,5 [M(Bp)2] complexes of first row transition metals are usually square planar or tetrahedral.6,7 Some octahedral anionic [M(Bp)3]-species of low stability can be also isolated.8,9 Five-coordinate anionic species [MX(Bp)2]- (M = Cr, Mn X = halides or pseudohalides) have been also known.10,11... 

Available structural details for these silicates, and for the wide range of other known species containing Mn" and silicate, are summarized in Table 23. Coordination numbers four (tetrahedral), five (both square pyramid and trigonal bipyramid and in-between structures), six (mainly octahedral and distorted, but including one trigonal prism), seven (of various shapes) and eight (dodecahe-dra and distorted rhombohedra) all are defined and there is evidence for three-coplanar in a zeolite the hydrated form is five-coordinate (3 x 2.28 A and 2 x 2.05 A) but, on dehydration of this Mn-exchanged zeolite, the solid contains planar three-coordinate Mn with Mn—O = 2.11 A, ... 

A final question concerns the unusual core conformation of all of the four- and five-coordinate rt-cation radical species listed in Table XI. All these species have an unusual saddle-shaped conformation. Possible reasons for this are to be described in the conformation section. 

The strategy used to design active and selective catalysts was based on the following five factors for regulation, (i) conformation of ligands coordinated to Rh atom (ii) orientation of a vacant site on Rh (iii) cavity with the template molecular shape for reaction space produced behind template removal (iv) architecture of the cavity wall and (v) micropore in inorganic polymer-matrix overlayers stabilizing the active species at the surface [46, 47, 71]. 

The presence of one or several nitrides is effective at modifying the metal cluster structure. Face bridging naked nitrides are not known but a nitrogen atom with a T-shaped coordination has been found in [Mo3(N )(0)(C0)4(C5H5)3]. Semi-exposed nitrides have been found in the species with four or five metal atoms they are invariably encapsulated into clusters of higher nuclearity. All the tetranuclear... 

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