Coordinated bonds

The physical properties of amine oxides are attributed to the semipolar or coordinate bond between the oxygen and nitrogen atoms with high electron density residing on oxygen. 

Eig. 1. Types of chelates where (1) represents a tetracoordinate metal having the bidentate chelant ethylenediamine and monodentate water (2), a hexacoordinate metal bound to two diethylenetriamines, tridentate chelants (3), a hexacoordinate metal having triethylenetetramine, a tetradentate chelant, and monodentate water and (4), a porphine chelate. The dashed lines iadicate coordinate bonds. 

The properties of copper(Il) are quite different. Ligands that form strong coordinate bonds bind copper(Il) readily to form complexes in which the copper has coordination numbers of 4 or 6, such as tetraammine copper(Tl) [16828-95-8] [Cu(NH3)4], and hexaaquacopper(Il) [14946-74-8] [Cu(H,0),p+ ( see Coordination compounds). Formation of copper(Il) complexes in aqueous solution depends on the abiUty of the ligands to compete with water for coordination sites. Most copper(Il) complexes are colored and paramagnetic as a result of the unpaired electron in the 2d orbital (see Copper... 

Zirconium. Zirconium 2-ethyIhexanoate [22464-99-9] is classified as an auxihary drier and is the most widely used replacement for lead. Zirconium improves through dry mainly by the formation of coordination bonds. It has excellent color, a low tendency to yellow, and better durability compared to other auxiliary metals. 

A large number of polymers have been prepared in the laboratory in which coordinate bonds play a significant role. Probably the most investigated are the bis-(3-diketone polymers, of which one type is shown in Figure 29.23. 

Fig. 15. Growth of a (5ii,5n) tubule on the catalyst surface, illustrated by that of the (5,5) tubule. The central grey circle represents the catalyst particle with 10 coordination sites, and the small grey circles represent the other 10 catalyst coordination sites. The normal and bold lines represent single and double bonds, respectively, while coordinative bonds are represented by dotted lines [(a), (b) and (c)] (a ), (b ) and (c ) are the corresponding planar representations.

Growth mechanism of a (9n,0) tubule, over 24n coordination sites of the catalyst. The growth of a general (9 ,0) tubule on the catalyst surface is illustrated by that of the (9,0) tubule in Fig. 16 which shows the unsaturated end of a (9,0) tubule in a planar representation. At that end, the carbons bearing a vacant bond are coordinatively bonded to the catalyst (grey circles) or to a growing cis-polyacetylene chain (oblique bold lines in Fig. 16). Tlie vacant bonds of the six c/s-polyacetylene chains involved are taken to be coordinatively bonded to the catalyst [Fig. 16(b)]. These polyacetylene chains are continuously extruded from the catalyst particle where they are formed by polymerization of C2 units assisted by the catalyst coordination sites. Note that in order to reduce the number of representations of important steps, Fig. 16(b) includes nine new Cj units with respect to Fig. 16(a). 

The 12 catalyst coordination sites — drawn further away from the surface of the particle (closer to the tubule) — are acting in pairs, each pair being always coordinatively bonded to one carbon of an inserted (F) or of a to-be-inserted (2 ) Cj unit and to two other carbons which are members of two neighbouring cis-polyacetylene chains (3°). It should be emphasized that, as against the (5n,5n) tubule growth, the C2 units extruded from the catalyst particle are positioned in this case parallel to the tubule axis before their insertion. 

We are interested in the H-H bond length, so we specify the coordinate bonding those two atoms to the AddRedundant option so that its value will be included in the printout of the optimized structure (the Si-H bond lengths will be included by default). 

N occupy an sp lone-pair in the plane of the ring (or the plane of the local PNP triangle) as in Fig. 12.26a. The situation at P is less clear mainly because of uncertainties concerning the d-orbital energies and the radial extent (size) of these orbitals in the bonding situation (as distinct from the free atom). In so far as symmetry is concerned, the sp lone-pair on each N can be involved in coordinate bonding in the jcy plane... 

The concept of the coordinate bond as an interaction between a cation and an ion or... 

Compared to later elements in their respective transition series, scandium, yttrium and lanthanum have rather poorly developed coordination chemistries and form weaker coordinate bonds, lanthanum generally being even less inclined to form strong coordinate bonds than scandium. This is reflected in the stability constants of a number of relevant 1 1 metal-edta complexes ... 

Over the years, geometry optimization has become an essential part of ab initio methodology. Research papers simply don t get published unless they report a geometry optimization. Almost all of the early ab initio packages made use of internal coordinates (bond lengths, bond angles and dihedral angles), as defined by the Z-matrix discussed in Chapter 1. The reason for the popularity of the... 

Cu(II) and these complexes may by an octahederal structure due to formation of coordination bonds between the amide group and water of hydration with Cu(II) (2) the polymer chains form hydrogen bonds with... 

Water may form coordinate bonds with ions or... 

When, however, the ligand molecule or ion has two atoms, each of which has a lone pair of electrons, then the molecule has two donor atoms and it may be possible to form two coordinate bonds with the same metal ion such a ligand is said to be bidentate and may be exemplified by consideration of the tris(ethylenediamine)cobalt(III) complex, [Co(en)3]3+. In this six-coordinate octahedral complex of cobalt(III), each of the bidentate ethylenediamine molecules is bound to the metal ion through the lone pair electrons of the two nitrogen atoms. This results in the formation of three five-membered rings, each including the metal ion the process of ring formation is called chelation. 

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