Metal coordination bond

In all the above reactions the hydrido phosphorus centre acts as a pen-tavalent phosphorus. Interesting reactions are known in which the tautomer of the hydridophosphazene containing a P(III) centre acts as a trivalent phosphine towards transition metals. Thus N3P3Ph4(Me)H on treatment with MCI2 (M = Pd, Pt) [246] or AUCI3 [247] results in complexes [N3P3Ph4(Me)H]2 MC1 (M = Pd or Pt n = 2, M = Au n = 3). These complexes have been shown to possess phosphorus-metal coordinate bonds (Eq. 49). 

Template-metal coordinative bonds have also been used in the imprinting and recognition of carbohydrates in aqueous media. A MIP, templated with glucose and using 4-(iV-vinylbenzyl)diethylenetriamine)Cu(H)]diformate as... 

One of the best known examples of reversibility in bond formation is the cross-linking of cysteine, a sulfur-containing amino acid, that affects tertiary structure in proteins and, ultimately, macroscale phenomena such as the degree of curl in hair. Other examples include the imine bond, formed by the reaction of an amine group with an aldehyde, and metal coordinate bonds to atoms such as nitrogen as found in many enzymes. 

The immobilization of a large volume of liquid by a small quantity of gelator is achieved efficiently if the elementary assemblies are rodlike and have large aspect ratios. Such linear structures are determined by specific binding forces associated with the chemical constitution of the gelators. In nonaqueous liquids, the attractive forces are mainly the van der Waals type and can be supplemented by dipolar interactions, intermolecular hydrogen bonds, metal-coordination bonds, or electron transfers, etc. 

Fig. 3. Diagrammatic representation of the four molecular orbitals composing the bisligand-metal coordinate bond...

Whe can briefly summarize the case for acetylenes. A single metal can, in an allowed manner, fuse two acetylene n bonds to two a bonds this is represented by 28 - 29. But 29 is not a representation of a cyclobutadiene-metal coordinate bond 30 < -31 is. Full cyclobutadiene-metal bonding can be generated across the reaction coordinate by introducing a second metal (32) that operates on the second set of n bonds as the first does, thus giving 33 34. 

Hydrogen bonds and metal coordination bonds have been the mainstay of the supramolecular chemist when it comes to the intentional manipulation of noncovalent interactions. However, nature s examples teach us the power of using weak, non-directional interactions to stabilize the folded state and deepen the folding funnel. Thus, van der Waals and solvophobic interactions are crucial to foldamer design, although they have been scarcely utilized in synthetic systems. In the simplest sense, such input is realized by incorporating amphiphilic character into the chain. 

In a third approach, supramolecular polymers are based on the reversibility of metal-coordination bonding. These polymers are the closest analogues to conventional macromolecules, because most of the polymers disclosed make use of strong bonding,16 in which the reversibility can be tuned by chemical means only. However, appropriate choice of the metal ion can give rise to bonding that resembles that of the other two approaches. The DP of the polymers in the case of the coordination polymers is similar to that of the condensation polymers, and achieving exact stoichiometry is of distinct importance here. 

B. Divalent Organotin Compounds Containing a Tin-Transition Metal Coordination Bond... 

A self-assembly reaction that involves the connection of individual building blocks via noncovalent interactions permits the rational integration of desired functional groups into the resulting molecules. Transition metal coordination bonds have been exploited in the synthesis of numerous metal-based supramolecular architectures in recent years. Complexation of metal ions to multidentate ligands generates equilibrium mixtures of various structures based on numerous possible combinations of metals and ligands.In the situation of thermodynamic control (see Thermodynamics Laws), the... 

Complete 3D solution structures have been determined by NMR experiments for three invertebrate Cd -MT forms, one from echinoidean and two from crustacean species. The structure of the sea urchin S. purpuratus) " Cd7-MTA consists of two globular domains, an N-terminal Cd4(SCys)ii and a C-terminal Cd3(SCys)9, whose metal cluster topology compares well with the corresponding analogues in mammalian MT. Combined with this similarity, there is an inverted arrangement of the three and four metal clusters, and thus of the a and (3 domains, as well as a significantly different connectivity pattern for the Cys-metal coordination bonds in the two... 

In order to form open porous structures rigid building blocks capable of forming intermolecular hydrogen bonds or metal coordination bonds are... 

Complexation of cellulose ether with some transition metals does not behave in the same manner as that observed for parent cellulose ether (i.e., the number of degradation stages was increased and order of degradation were varied). This is due to the elimination of coordinated water and decomposition of cellulose ether-metal coordination bonds. 

Rotaxanes are considered to be one typical prototype of molecular devices machines, because they have a rooter and an axle in the molecule. a-Cyclodextrin was first used as a rotor of rotaxane by Ogino et al. in 1978. ° They used metal complexes as stoppers. Since then some rotaxanes containing cyclodextrins have been reported (Fig. 1.20). Most of them used metal complexes as stopper groups. However, the metal coordination bonds are so weak that cyclodextrin rings may escape from the bond. All the rotaxanes reported are ionic so as to solubilize the rotaxanes in water, except one example in which all the components are non-ionic and soluble in organic solvents." In this case there are some inter-... 

Other issues involved are translational and rotational freedom of the surfactant molecules individually dispersed in the solvent and the loss of this freedom in the aggregated state, as also hydrogen bonding and metal coordination bonding when they do exist between the head-groups. 

Type III The metal is part of a polymer chain or network. This type considers homochain or heterochain polymers with covalent bonds to the metal, coordinative bonds between metal ions and a polyfunctional ligand (coordination polymers), Ti-complexes in the main chain with a metal, cofacially stacked polymer metal complexes and different types (polycatenanes, polyrotaxanes, dendrimers with metals) (Figure 3). 

Although the log values for first complexations of lns(l,4,5)P3 with (5,5)-and [(R,R)-35f were nearly identical, the differences in thermodynamic parameters (enthalpy and entropy changes) suggest different binding modes for the two combinations. These results provide important information about the design and synthesis of chemical receptors, sensors, and inhibitors for lns(l,4,5)P3 and related compounds such as Ptdlns(4,5)P2, and for the design of supramolecular complexes using phosphate-metal coordination bonds. 

Heterocycles are widely employed as useful building blocks in the construction of molecular recognition and supramolecular assembly systems [1]. These provide hydrogen bondings, electrostatics, metal coordination bonds, 7t-7t interactions, and other attractive weak forces with various species both in the solution and the solid states. Since several famihes of heterocycles further exhibit electrochemical activities, photochemical reactivities, optical characteristics, and other functions, current heterocyclic chemistry offers a robust basis for sophisticated molecular architectures toward molecular recognition and supramolecular assembly. 

In addition to metal coordination bonds, hydrogen bondings, electrostatics, and 7T-7T interactions, the attractive interaction between the curved r-surface of a fullerene and the flat rr-surface of a porphyrin was recently reported [8,9]. When the fullerene and the porphyrin were linked covalently in the single molecule (see 6), the two functions interacted with each other to form a supramolecular assembly in the solid state. In contrast to this divergent system, macrocycle 7 was prepared from the fused zinc porphyrins for the convergent interaction with specific guests. Since 7 had space to accommodate two fuUerenes, this kind of interaction operated well in the supramolecular assembly and moleciflar recognition systems. 

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