Coordination linked

Fig. 4.16 provides an illustration of the adsorption of a neutral polymer, polyvinyl alcohol, on a polar surface, and the resulting effects on the double layer properties. Adsorption of anionic polymers on negative surfaces - especially in the presence of Ca2+ or Mg2+ which may act as coordinating links between the surface and functional groups of the polymer - is not uncommon (Tipping and Cooke, 1982). 

This event leads to the formation of an electron donor-acceptor (EDA) complex involving the formation of a coordinate link between D and M. The availability of the additional electron pair at M causes an increase in electron density at X due to further polarization of the M-X bond. It is apparent that the amount of polarization will depend on both the polarizability of the covalent bond as well as the extent of interaction between D and M. For a given substrate the latter will depend on the donor properties of the donor8). 

The EPD functions at the oxygen atoms are also available for interaction with one more chromium trioxide molecule. Since the oxygen in the chromate ion has weaker EPD properties than the uncoordinated oxide ion, its interaction with the second chromium (VI)-oxide molecule is weaker than with the first one, and the chromium-oxygen bond distances in the newly attached CrOa unit show a less marked increase. At the same time the formation of a strong coordinate link from one oxygen of the chromate ion induces EA function in the chromium so that it... 

A somewhat different problem occurs in the question of the structure of, say, the phosphine oxides, the phosphine methylenes or the sul-phoxides. Again in a 3s3p framework the structure of triphenyl phosphine oxide must be written with the oxygen attached by a conventional coordinate link. On the other hand the use of d-orbitals allows the removal of the excess negative charge on the oxygen atom by the formation of a t-bond (Fig. 3). 

These structures, together with potentiometric measurements, allowed proposals to be made as to the probable mode of interaction between Ag+ ions and polyuridine (polyU). For pH < 6, Ag2(polyU)2 was considered the predominant species, whilst for pH >6, Ag(polyU)2 became increasingly important. Equilibrium constants were calculated for these 2 2 and 2 1 complexes as log j822= 12.1 and log/J12 = 9.3. Ag(polyU)2 was considered to have linear coordination while Ag2(polyU)2 was predicted to have, in addition to the N coordination, links through the 0-4 atoms. 

It can share a pair of electrons to form a coordinate link, as it does in coordination compounds. In most of these, it appears to coordinate as the positive ion, by transfer of an electron to an acceptor metal, which is [hereby reduced by 1 unit in oxidation state This causes, in some cases, the need for placing a negative charge on the metal. To avoid this. Pauling assumed the presence of four bonding electrons, involving structures of the type... 

The sheets formed by the apices of the tetrahedra are completed by hydroxyls and magnesium ions in octahedral coordination link the sheets. The one structural arrangement has nine octahedral sites and the other only eight. Both structures have channels on both sides and top and bottom of each ribbon which contains water molecules (zeolitic water). Additional water is bound to the edge of the ribbons and hydroxyls occur in the structure proper. 

Quevauviller, P, U. Borchers, and B.M. Gawlik. 2007. Coordinating links among research, standardisation and policy in support of water framework directive chemical monitoring requirements. J. Environ. Monit. 9 915-923. 

The second formula means merely that the HC1 molecule is a resonance hybrid between the ionic molecule H+Cl" and the molecule with the purely covalent bond, the direction of the arrow giving the direction in which the electrons have, on the average, been displaced (66). As, however, such an arrow is used by others (57), for indicating a coordinate link (semipolar double bond) caused by a lone electron pair of the donor atom, which likewise produces a dipole with its positive end on the donor side and its negative one on the acceptor side, the author suggests that the symbol — be used for the normal covalent bond, which, by resonance with an ionic structure, possesses a dipole. The point of this half arrow also indicates the direction of the negative end of the dipole. The full arrow — will then be reserved for the coordinate link. Both links play their roles in chemisorption, and it may be useful for the purposes of this article to introduce relatively simple symbols. According to this principle HC1 should be formulated as H—1-Cl. 

The former is bound by a coordinate link, aided by an image force of the ionic charge, which, however, is rather weak here because of the relatively large distances of the negative excess charges from the metal. The sulfate ion exhibits this image force only. In both cases there are the van der Waals forces as well, which also will be weak here. 

Suhrmann (62) explains the strong increase of the normal photoelectric effect of metals caused by the adsorption of water molecules and also by the molecules of ammonia, by accepting similar coordinate links to function in the chemisorption of these molecules. Dipoles are formed which point with their positive poles away from the surface, thereby decreasing the work function and, consequently, increasing the normal photoelectric effect ... 

Another, more direct, indication is obtained from the work of Dilke, Eley, and Max ted (85), who found from the change in magnetic susceptibility of palladium on adsorption of dimethylsulfide that an electron of the sulfide had entered the d band of the metal. As we saw in Sec. V,8,b, a coordinate link is formed in this case. 

Copper acetate as a catalyst is superior to other metal salts this can be explained by its ability to form complexes both with oligoalkylhydridesi-loxane and with the fibre due to coordination linking. The reactivity of the complex creates favourable conditions to form a branched cross-linked structure of the polyorganosiloxane film. 

Now we can write the expression for total potential using the addition theorem8 in local coordinates linked with the k -th sphere. Because the variables are separated we can find derivatives directly, then calculate their value on surface of the k - th sphere.The expansions of the potentials and their... 

Sidgwick, Some Physical Properties of the Coordinate Link in Chemistry, Cornell University Press, Ithaca, N. Y. (1933). 

The term is preferred to the obsolescent synonyms coordinate link , co-ordinate covalence , dative bond semipolar bond . 

Lowry and Sidgwick used for this bond between nitrogen and oxygen the names semi-polar double bond (covalent bond + ionic bond) or coordinate link and the symbol — The direction of the arrow indicates the direction of the electron transfer, thus... 

Panchenkov s viscosity formula, 89 paper chromatography, 182 Papin s digester, 276 parabola, 421 paraboloid, 429, 430 parachor, 144, 159 atomic, 144 bibliography on, 148 and bond-type, 147 constitutional effect on, 144 and coordinate link, 144 and dipole moment, 146 and entropy, 147 and latent heat of evaporation, 323 and latent heat of fusion, 146 and magnetic susceptibility, 147 for mixtures, 145 negative, 147 and refractivity, 146-7 in solution, 145 and space-filling fraction, 146 and space-filling, 146 ... 

A representative example of multiporphyrin species in which the subunits are assembled by relatively weak coordination links is the three-chromophore species studied by Hunter and Hyde (Figure 12). In this system, the light absorbed by the zinc porphyrins is partially transferred to the free-base porphyrin subunit [34]. 

Back in 1899, Werner and Stiasny (49) had studied the action of nitric acid on azobenzene and produced a series of nitro-azobenzenes and nitro-azoxybenzenes, but Werner carried the work no further. Werner then became interested in the analogy between the lakes of mordant dyes and the metallic derivatives of /3-diketones and proposed the view that mordant dyes were internal metallic complexes. This resulted in three papers published in the 1908-09 period. The first (43) reporting the complex metal salts formed from oximes, diketones, and several metals, came to the conclusion that the formation of mordant dyes depends on the formation of complex metal salts. He found that dyes capable of combining with mordants possessed both a salt-forming complex and a group capable of forming a coordinate link with a metal ion. 

This resolution (1927) showed that the salt must have the constitution XIII, and furthermore that the five-membered ring system of XIII was more stable than the six-membered ring system of XIV because the compound XIII was formed to the apparently complete exclusion of the compound XIV. This was moreover the first decisive example of a carbon atom becoming asymmetric by the operation of a coordinate link 17, 30). 

The broken lines represent the edges of the tetrahedron formed by the four copper atoms, the apex formed by the central copper atom being tilted to show all the bonds joined to this atom. The iodine atoms are depicted on the faces of the tetrahedron in order to show their linkage to the neighboring copper atoms. Actually, they lie well above the plane of the tetrahedral faces. The iodine atom on the rear face of the tetrahedron is not shown. The unbroken lines without barbs represent covalent links those with barbs represent coordinate links. These are formal linkages, but all the Cu-I links are of course identical 36). 

Reports of nucleophilic attack at atoms other than those above have also appeared. A kinetic study has compared the effectiveness of tertiary phosphines and phosphite esters in the catalysis of the cleavage of the silicon-silicon bond of methylchlorodisilanes, providing evidence for the involvement of a stabilised silylene intermediate. The anion of the y-phosphino-p-diketimine (197) has been shown to react with arsenic trichloride to give the phosphino-arsino-p-diketimine (198), in which there is a coordinative link from phosphorus to arsenic. ... 

---