Coordination numbers greater than

X Me Second cation present, with coordination number greater than 6 (second cation s ionic radius > tantalum/niobium ionic radius) Only cations that can fit into/occupy octahedral voids are present (second cation s ionic radius tantalum/niobium ionic radius)... 

Coordination Numbers Greater Than Four for Period 2 Elements... 

Although there are a relatively large number of N(+V) molecules, the absence of any with a coordination number greater than four must be attributed to the small size of the nitrogen... 

Much of what has been said so far in this chapter applies equally well to complexes of second- and third-row transition metals. However, there are some general differences that result from the fact that atoms and ions of the second- and third-row metals are larger in size than those of first-row metals. For example, because of their larger size (when in the same oxidation state as a first-row ion), ions of metals in the second and third rows form many more complexes in which they have a coordination number greater than 6. Whereas chromium usually has a coordination number of 6, molybdenum forms [Mo(CN)8]4 and other complexes in which the coordination number is 8. Other complexes of second- and third-row metals exhibit coordination numbers of 7 and 9. 

Polymerization in electrostatic systems like the ones mentioned above is stericaUy inhibited by alkyl substitution at the a-carbon which must assume a coordination number greater than 4. Coates and Glockhng have treated this inhibition of polymerization in terms of decreased electronegative character of the branched alkyl groups. Therefore, stimulated by the idea that f-afkylhthium compounds may exist as low polymers or even as monomeric molecules, Weiner and coworkers and Kottke and Stalke have isolated f-butyllithium as a pure substance for the first time and characterised it by spectroscopic methods and X-ray diffraction. The colourless crystalline solid was found to be tetrameric over a range of concentrations in both benzene and hexane ... 

Among the compounds that form complexes with silver and other metals are benzene47 (represented as in 6) and cyclooctatetraene. When the metal involved has a coordination number greater than 1, more than one donor molecule participates. In many cases, this extra electron density comes from CO groups, which in these complexes are called carbonyl groups. Thus, benzenechromium tricarbonyl (7) is a stable compound.4 Three arrows are... 

Different geometrical arrangements of the atoms attached to the central atom are possible for all coordination numbers greater than one. The coordination polyhedron (or polygon in planar molecules) may be denoted in the name by an affix called the polyhedral symbol. This descriptor clearly distinguishes isomers differing in the geometries of their coordination polyhedra. 

It was shown (17) that phosphine exchange occurred in [AuMe(PR3)l complexes, but species with a coordination number greater than two were not observed, even with bidentate phosphorus ligands. Although such species were not observed, an associative mechanism was thought to be operative (16, 18). With trimethylphosphite also, only the two-coordinate complex [AuMe P(OMe)3 l was detected in solution (19). 

Nonexistent atoms used for the definition of a structure if the program does not allow a specific connectivity (e. g., coordination numbers greater than four) or if certain interactions and geometries (e. g., Jahn-Teller distortions, planarity of a system such as a square planar nickel(II) complex) can not be modeled in another way. 

Restricted to the use of only four valence orbitals, Be very rarely attains coordination numbers greater than four higher coordination numbers are more common for Mg, whose 3d orbitals may be invoked. 

In contrast to the heteroatom-substituted plumbylenes, a few plumbylenes bearing only carbon substituents have been reported. Some of them are stabilized by intramolecular coordination of the lone pair of a donor group in the organic substituent, thus giving the lead a coordination number greater than 2 as can be seen in the diarylplumbylene RjPb... 

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