Auto-complex formation

Mercury(II) halides are too covalent to allow the free Hg + to appear its presence must be associated with auto-complex formation. Thus HgClg dissociates only slightly and then in an unusual way ... 

On the basis of the conductivity of the solution, Gutmann and Wegleitner [Gu 70] assumed the occurrence of auto-complex formation in nitrobenzene. The results of Mossbauer studies suggest that this assumption is probably incorrect the following equilibrium, proposed by de Main [De 59], is presumably established in the solution ... 

Important roles in the determination of the solution structure are played by the various, more complicated equilibria, also, e.g., solvent-induced auto-complex formation and the formation of mixed ligand and polynuclear complexes. 

The simplest form of auto-complex formation is illustrated by the equation... 

The role of auto-complex formation can be well seen, for example, in solutions of tin(IV) iodide in non-aqueous solvents [Ma 70]. When donor solvents are added to solutions of tin(IV) iodide in a non-coordinating solvent (e.g., nitrobenzene), the following equilibria may be assumed ... 

Auto-complex formation, although less marked, can also be detected in iron(III) chloride solutions [Gu 70] the equilibria are as follows ... 

It is worthy of special mention that auto-complex formation similarly occurs in the case of metal carbonyls when acted upon by high-donicity molecules [Ch 68, Hi 57a, Hi 57b, Hi 65]. This process is well illustrated by the following equation ... 

Cobalt (II) iodide is subject to auto complex formation in TMP and it is ionized in TMP, DMF, DMA and DMSO. Nickel iodide is completely ionized in TMP and DMS02. Tin(IV) iodide, bismuth(III) iodide, antimony(III) iodide, lead(II) iodide and cadmium (II) iodide are considerably ionized in DMF and completely ionized in DMSO. ... 

Nickel(II) chloride has somewhat lower solubilities than cobalt(II) chloride. NiCla" and NiCl4 are produced in acetonitrile and also in trimethyl phosphate where auto complex formation is appreciable . In tributyl phosphate the units were not identified with certaintyi, but very low stabilities of the chloride-coordinated nickel species are indicated. 

The second important feature of the reaction mechanism of the epoxy compound curing under the action of amines (primary, secondary and tertiary) and their mixtures consists in formation of various hetero-, auto-, inter- and intramolecular donor-acceptor complexes between the components of the reaction system — the starting substances and reaction products. Consideration of this complex formation can adequately explain the reaction kinetics. 

A typical example of a salt that forms auto-complexes is ZnCl2. The formation of complexes at melting takes place according to the scheme... 

Lithium alkyls in ether or benzene show a mean degree of association of from three to seven, whereas phenyl- and benzyllithium are dimeric in ether (17, 135). The lower degree of association in ether may stem from etherate formation. The structure of these auto-complexes may be analogous to that of beryllium and aluminum alkyls, or perhaps a lithium atom acts as a Lewis acid that is, Li [Li(C6H6)2]e. Wittig (135) favors this formulation over a phenyl bridging scheme. 

Formation of auto-complexes, mixed ligand complexes,... 

Mixed complex formation has been postulated in the oxidation of sulphite catalysed by transition-metal ions. Several reactions are observed in the presence of copper(ii). The auto-oxidation rate is catalysed with formation of the species [00(803)202] " as intermediate. In the presence of propan-2-ol (ROH), however, an inhibition reaction, dependent on [SOs ] and [ROH], is observed. Induced oxidation of the inhibitor by copper(n) is also a factor, the rate being a function of [Cu ]. In the latter system the complex [Cu(SO )-(R0H)02] is considered as the reactive species,... 

On the other hand, another study of complex formation between adrenaline (or noradrenaline) and Cu " showed that with catecholamine Cu ratios 2, 2 1 complexes involving the o-diphenol system were formed, which were fairly stable with respect to oxidation. With a catecholamine Cu ratio of approximately 1 1 however, it was believed that a 1 1 complex was formed initially, but this rearranged to a 4 4 complex including both the phenolic group and the side chain. This may then auto-oxidise and interaction between the Cu and the side chain may be responsible for the... 

This solvent prevents the dipole-dipole interaction of the -CN groups and thus, prevents the formation of the pre-oriented association complex which favours propagation and is thus responsible for auto-acceleration. 

Abstract. Auto-accelerated polymerization is known to occur in viscous reaction media ("gel-effect") and also when the polymer precipitates as it forms. It is generally assumed that the cause of auto-acceleration is the arising of non-steady-state kinetics created by a diffusion controlled termination step. Recent work has shown that the polymerization of acrylic acid in bulk and in solution proceeds under steady or auto-accelered conditions irrespective of the precipitation of the polymer. On the other hand, a close correlation is established between auto-acceleration and the type of H-bonded molecular association involving acrylic acid in the system. On the basis of numerous data it is concluded that auto-acceleration is determined by the formation of an oriented monomer-polymer association complex which favors an ultra-fast propagation process. Similar conclusions are derived for the polymerization of methacrylic acid and acrylonitrile based on studies of polymerization kinetics in bulk and in solution and on evidence of molecular associations. In the case of acrylonitrile a dipole-dipole complex involving the nitrile groups is assumed to be responsible for the observed auto-acceleration. 

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