Interactions coordination

Coordination interaction appears if an electronic pair of one subsystem (electron donor) lowers its energy by interacting with an electron acceptor offering an empty orbital, e.g., a cation (acceptor) interacts with an atom or atoms (donors) offering lone electronic pairs. This may be also seen as a special kind of electrostatic interaction. Fig. 13.15.a shows a derivative of porphyrin as well as a ciyptand (the name comes from the ritual of burying the dead in crypts), Fig. 13.15.b, the compounds offering lone pairs for the interaction with a cation. 

Let us consider a water solution containing ions Li , Na , K , Rb+, Cs . After adding the above mentioned cryptand and after the equilibrium state is attained (ions/cryptand, ions/water and cryptandAvater solvation), onty for K wUl the equilibrium be shifted towards the K+Zcryptand complex. For the other ions the equilibrium will be shifted towards their association with water molecules, not the cryptand. This is remarkable information. 

Supramolecular Chemisliy , Institute of Physical Chemistiy Publications, 1993, p. 88 the equilibrium constants of the ion/oyrptand association reactions are for Li, Na+, K+, Rb+, Os+ 

We are able to selectively extract objects of some particular shape and dimensions (recognition). 

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Fig. 2. Classification/nomenclature of host—guest type inclusion compounds, definitions and relations (/) coordinative interaction, (2) lattice barrier interaction, (J) monomolecular shielding interaction (I) coordination-type inclusion compound (inclusion complex), (II) lattice-type inclusion compound (multimolecular/extramolecular inclusion compound, clathrate), (III) cavitate-type inclusion compound (monomolecular/intramolecular inclusion...

In 1963, Dauben and Berezin published the first systematic study of this syn directing effect (Scheme 3.15) [37]. They found that the cyclopropanation of 2-cyclohexen-l-ol 32 proceed in 63% yield to give the syn isomer 33 as the sole product. They observed the same high syn diastereoselectivity in a variety of cyclic allylic alcohols and methyl ethers. On the basis of these results, they reasonably conclude that there must be some type of coordinative interaction between the zinc carbenoid and the substrate. 

The discovery of viable substrate-direction represents a major turning point in the development of the Simmons-Smith cyclopropanation. This important phenomenon underlies all of the asymmetric variants developed for the cyclopropanation. However, more information regarding the consequences of this coordinative interaction would be required before the appearance of a catalytic, asymmetric method. The first steps in this direction are found in studies of chiral auxiliary-based methods. 

Finally, a number of industry cngiiiceriiig experts and industi-y engineering organizations voiced concern that the electric grid may become less reliable after restructuring. The operation and maintenance of the North American electric grid depends on the coordinated interaction of more than a hundred control... 

The role of coordinated ethylene is evidenced by the recent ab initio calculation performed by Espelid and Borve [121-123], who have shown that ethylene may coordinate in two different ways to the reduced Cr(II) species, either as a molecular complex or covalently bound to chromium. At longer Cr-C distances (2.36-2.38 A) an ethylene-chromium zr-complex forms, in which the four d electrons of chromium remain high-spin coupled and the coordination interaction is characterized by donation from ethylene to chromium. Cr(II) species in a pseudo-tetrahedral geometry may adsorb up to two equivalents of ethylene. In the case of a pseudo-octahedral Cr(II) site a third ethylene molecule can also be present. The monoethylene complex on the pseudo-tetrahedral Cr(II) site was also found to undergo a transformation to covalently bound complex, characterized by shorter Cr-C distances (about... 

The rapid and reversible formation of complexes between some metal ions and organic compounds that can function as electron donors can be used to adjust retention and selectivity in gas and liquid chromatography. Such coordinative interactions are very sensitive to subtle differences in the composition or stereochemistry of the donor ligand, owing to the sensitivity of the chemical bond towards electronic, steric and strain effects. A number of difficult to separate mixtures of stereoisomers and isotopomers have been separated by complexation chromatography. 

Fig. 32. Crystal packing diagram for 77, suggestive of polymerization through nitro-zinc coordination interactions.

A shift of stretching vibrations vc=0 from 1590 to 1640 cm-1 is observed in the mixture of model compounds which points to intermolecular coordination interactions. 

It is likely that the observed coordination interaction between individual segments of the macroradicals and monomer units determines the stereoorientation of free-radical copolymerization of organotin methacrylates with MA. 

The observed anomaly in the viscous properties of dilute organotin copolymer solutions seems to be attributable to the existence of both intra- and intermolecular associates,due to coordination interactions between SnR3 and C=0 fragments of side groups. 

Since spontaneous polymerization is only observed in contact with air or in undesiccated benzene used as a reaction medium, it is natural to attribute this phenomenon to the catalytic effect of traces of water on the opening of the oxirane ring involved in the coordination interaction with the tin atom. 

Substitution of cyclopropane rings with the alkenyl group permits unique ring transformations based on metal coordination interaction with four -electrons. The transition-metal-induced ring-opening rearrangement also results in the formation of metallacycles. Further elaboration is attained by insertion and reductive elimination. 

The replacement of groups with weak coordination interaction, including substitution of the edge and terminal ligands, plus the alteration of lanthanides, may be of help in the design and synthesis of a large variety of 3d-4f clusters. This approach is attractive and it may open up new routes for the construction of other polynuclear complexes. A similar situation also applies to analogous Zn2+ and Co2+ clusters. 

It should be noted that the hypovalent Lewis acid-base interactions of the present section are in principle closely related to the general metal-ligand coordination interactions discussed in Section 4.5. However, in normal-valent transition-metal... 

Other sensors are mostly grouped towards the triethylamine. In the case of porphyrins 6-8, 13 the coordinated metal is no longer able to drive the selectivity pattern and the presence of the peripheral alkyl chains completely shadows the coordination interactions. This result can explain the failure to observe the coordination interaction in the sensing mechanism of the metal complexes of the closely related alkyl chains functionalized phthalocyanines reported in the past by Gopel and coworkers [22]. 

Most network structures involving crown ethers are simple hydrogen bonded chains where the crown forms second sphere coordination interactions with a complex ion. These are known for [18]crown-6, [15]crown-5 and [12]crown-4 hosts with a variety of metal complexes [17-25]. For instance when combined with the small [12] crown-4, the perchlorate salts of Mn(II), Ni(II) and Zn(II) form polymeric chain structures with alternating crown ethers and [M(H20)6]2+ cations [19]. Similarly the larger [18]crown-6 forms simple linear chains with metal complexes and cations such as fra s-[Pt(NH3)2Cl2] [20], [Cu(NH3)4(H20)]2+ (Fig.2) [21],and [Mg(H20)5(N03)] + [22],... 

Some emphasis is given in the first two chapters to show that complex formation equilibria permit to predict quantitatively the extent of adsorption of H+, OH , of metal ions and ligands as a function of pH, solution variables and of surface characteristics. Although the surface chemistry of hydrous oxides is somewhat similar to that of reversible electrodes the charge development and sorption mechanism for oxides and other mineral surfaces are different. Charge development on hydrous oxides often results from coordinative interactions at the oxide surface. The surface coordinative model describes quantitatively how surface charge develops, and permits to incorporate the central features of the Electric Double Layer theory, above all the Gouy-Chapman diffuse double layer model. 

The adsorption of humic and fulvic acids on surfaces can be interpreted along the scheme of Fig. 4.9c,d. Because of hydrophobic interaction humic and fulvic acids tend to accumulate at the solid-water interface. At the same time the adsorption is influenced by coordinative interaction, e.g., schematically,... 

How could one distinguish experimentally in the interaction of a hydrous oxide surface with a fatty acid, whether the interaction is due to hydrophobic bonding or to coordinative interaction (ligand exchange of the carboxyl group with the surface functional groups of the hydrous oxide) ... 

Vicentini and coworkers have reported the complexes of DPPA with lanthanide perchlorates 224), hexafluorophosphates 225), chlorides and nitrates 226). The anions in the perchlorate and hexafluorophosphate complexes are noncoordinated and hence the complexes are six coordinated. Conductance data for the nitrate complexes indicate that the coordination interaction between the lanthanide ion and the nitrate ion decreases along the lanthanide series 226). 

It is especially important to investigate the molecular structure of coordination compounds in the vapor phase because the relatively weak coordination interactions may be considerably influenced by intermolecular interactions in solutions and especially in crystals. It has been shown that the geometrical variations can be correlated with other properties of the molecular complexes ). In particular the structural changes in the F3B N(CH3)3 and CI3B N(CH3)3 molecules ) relative to the respective monomeric species unambiguously indicated boron trichloride to be a stronger acceptor than boron trifluoride. Data on the geometry and force field have also been correlated ). 

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