Coordination number five

Coordination compounds of vanadium are mainly based on six coordination, in which vanadium has a pseudooctahedral stmcture. Coordination number four is typical of many vanadates. Coordination numbers five and eight also are known for vanadium compounds, but numbers less than four have not been reported. The coordination chemistry of vanadium has been extensively reviewed (8—12) (see Coordination compounds). 

Mercury(II) arsenate Hg3(As04)2 has three independent Hg particles with coordination numbers five and seven, but each of them has two short Hg O bonds (206 < r(HgO) < 214 pm) in a nearly linear arrangement linking of these polyhedra including the As04 tetrahedra leads to a 3-D network.300... 

For a long time the coordination number six at silicon was discussed as the ultimate limit, but meanwhile, the coordination numbers five, seven and ten have also been verified ... 

RING COMPOUNDS OF PHOSPHORUS WITH COORDINATION NUMBER FIVE (PHOSPHORANES)... 

The synthesis, IR, 19F-NMR, and X-ray crystal and molecular structures of XV have been reported. It is the first well-characterized four-membered As—N ring compound with arsenic atoms of coordination number five. It has been prepared by the following reaction ... 

Both forms (110) and (111), give rise to the same equilibrium in solution. Some solvents favor the pentacoordinated form, while others favor the tetracoordinated form. As a result, there is a significant solvent dependence of the 81P n.m.r. shift, since the observed shift corresponds to the average value of the signals of the two types of phosphorus nuclei, S =ca. + 40 p.p.m. (vs. H8P04) for coordination number five, and ca. —40 p.p.m. for coordination number four, in this particular type of compound. The establishment of the equilibrium is fast in the time scale of n.m.r. 

Again a compound CoC12.3 CsCl is not a complex compound Cs3[CoCl5] with coordination number five but on the basis of its crystal structure it is a double salt Cs2[CoCl4].CsCl. 

Note Cobalt is more flexible in its coordination geometry than the group 10 metal meaning that cobalt tolerates the coordination number five rather than a positive charge. 

Various more specific stmctural-chemical problems addressed successfiilly with the use of the CSD are too numerous to list. Inter aUa, it was possible for the first time to clarify the stereochemistry of less common (and less regular) types of metal coordination, for example, with coordination numbers five and seven. ... 

All known Au compounds are diamagnetic ([Xe]4f " 5d low-spin configuration), and the large majority have square-planar geometry. However, Au complexes with coordination number five or six are also known. 

Although not applicable to nitrogen, which is necessarily limited to a covalence of four. Structures V and VI have been found for a number of compounds of other elements (14y 15), but Structure IV has not been found to correspond to any compound exhibiting coordination number five. 

Interest in such compounds has arisen as a result of the extensive studies being carried out on the stereochemical aspects associated with phosphorus in coordination number five. The observation of distinct axial and equatorial P—F environments for the tetrafluorophosphoranes, by NMR techniques, is possible, whereas this observation is not common to the corresponding hydrocarbon-phosphorus bonded tetrafluorophosphoranes. Further substitution at phosphorus is possible, the tetrafluorophosphoranes and trifluorophosphoranes are reactive compounds, and it is possible to substitute further F atoms for other groups. The experimental techniques described here can be applied to the preparation of other amino fluoro phosphoranes. Further, the same techniques are applicable to other reactions involving phosphorus-fluorine compounds and silicon compounds. 

The stereochemical features of the polymerization were satisfactorily accounted for by considering the nonbonded interactions between the monomer molecule undergoing insertion and the ligands on the vanadium atom. Coordination number five for vanadium was chosen to justify the more relevant data concerning the propylene polymerization and ethylene, 1-butene, and cis-2-butene copolymerization. 

The following points are of interest concerning polyhedra for coordination numbers five through nine. 

Coordination numberfive. The two possible polyhedra for coordination number five are the D3/, trigonal bipyramid for which the xp manifold is supplemented by the d(z ) orbital with two opposite major lobes and the 4 square pyramid for which... 

Coordination number six appears, from the limited available data, the most common (Table 7). Lower coordination numbers are known but appear to be fairly rare three is represented by some silylamides (Section 41.3.3.1) and in a dehydrated zeolite (Section 41.3.5.2.i) four-planar is known only for macrocyclic [N,] systems and as [MnOJ in a few unusual crystalline compounds and four-tetrahedral is well characterized but still apparently less common than for Zn, Co and possibly even Ni. Coordination number five is also known, but few examples are yet characterized. On the other hand, higher coordination numbers seven and eight are less unusual here—hardly surprising in view of the larger size of Mn". Examples include seven coordinate [Mn(edta)H20] (Section 41.3.9), [Mn(py3tren)] (Section 41.3.3.6) and an [Mn07] species (Section 41.3.5.3.iii), and eight coordinate [Mn(04)2] species (Section 41.3.5.4). 

---