Monomeric aluminium

Both these molecules exist in the gaseous state and both are trigonal planar as indicated by reference to Table 2.8. However, in each, a further covalent bond can be formed, in which both electrons of the shared pair are provided by one atom, not one from each as in normal covalent bonding. For example, monomeric aluminium chloride and ammonia form a stable compound ... 

This compound, which contains atoms arranged tetrahedrally around the boron atom, can readily be isolated from a mixture of dimethyl ether and boron trichloride. On occasions a chlorine atom, in spite of its high election affinity, will donate an electron pair, an example being found in the dimerisation of gaseous monomeric aluminium chloride to give the more stable Al2Clg in which each aluminium has a tetrahedral configuration ... 

The order of reaction with respect to aluminium chloride was ill-defined. Since nitrobenzene and aluminium chloride form a 1 1 complex which exhibits the simple monomeric molecular weight in nitrobenzene solution185, and since even in solutions of aluminium chloride and benzoyl chloride in nitrobenzene the aluminium chloride is preferentially associated with the solvent184, then in nitrobenzene solutions of aluminium chloride and benzenesulphonyl chloride the lesser basicity of the latter relative to benzoyl chloride means that the aluminium chloride must be mainly associated with nitrobenzene and in equilibrium with aluminium chloride associated with the sulphonyl chloride184. By analogy with... 

Bei der Reaktion wird Lithium-triathyl-hydrido-borat und monomeres Aluminium-tert.-butanolat gebildet, das durch Koordination die Aufspaltung des Ringes katalysiert4. 

A quantitative evaluation of the acid properties is quite difficult. One example is nevertheless quite instructive in l,3-di-tert-butyl-2,2-dimethyl-1,3,2,4L2-diazasila-stannetidine (1) the tin atom can be replaced by the much smaller aluminium-methyl group 124). While / is monomeric in benzene, 36 is dimeric ... 

Aluminium ions in AlCl3 solutions. We have performed the same type of studies by adding different amounts of copolymers and we have measured the decrease of monomeric Al ions concentration by increasing the polymer content. Figures 2 and 3 give some examples of results "Al bound" as measured by NMR is plotted as a function of pH, for two different systems and can be compared with the values calculated for K IO1 and KQ=1016. 

Current work in our laboratory [3] indicates that in methyl bromide solution the ionogenic reaction is of second order with respect to [AlBr3], and the same has been found [14] for the ionisation of A1I3, Gal3, and Inl3 in EtI. Since it is known that the aluminium halides are monomeric in these solutions, it follows that the rate-determining step for the selfionisation is the reaction (10) ... 

An important consequence of acidification is mobilization of metals from terrestrial watersheds [14]. Particularly important is the release of aluminium because of its toxic effects on freshwater biota especially on fish [15]. Not all A1 forms are toxic. Only cationic species contained within the operational forms termed labile A1 (LAI) or inorganic monomeric A1 (Ali) are gUl-reactive and hence affect fish health [16]. It has been shown that concentrations of soluble aluminium increase with decreasing pH from a pH of ca. 6.3 [17]. 

Orotic acid readily forms dimers even when irradiated in liquid medium [582, 583]. 5-Bromouracil (5-BrU) in DNA is dehalogenated, rather than forming cyclobutane-type dimers. Such DNA derivatives are more sensitive to ultraviolet irradiation than normal DNAs [584-594], Irradiation of 5-bromo-uracil and derivatives in aqueous medium produces 5,5 -diuracil [590, 591]. However, derivatives such as 3-sbutyl-5-bromo-6-methyluracil have been reported to yield cyclobutane dimers either by irradiation of frozen aqueous solutions, or by catalysis with free radical initiators, such as aluminium chloride, ferric chloride, peroxides or azonitriles [595]. 5-Hydroxymethyluracil is reported to dimerize very slowly in frozen water at 2537 A [596]. The fundamental research in the photochemistry of the nucleic acids, the monomeric bases, and their analogues has stimulated new experiments in certain micro-organisms and approaches in such diverse fields as template coding and genetic recombination [597-616]. 

The objective of the synthesis would be to maximise the first reaction (leading to ferrlslllcates) and suppress the formation of hydroxides of iron by the latter reaction by operating at low pH, using aluminium free source of Si and adjusting the reaction conditions to maximise the concentration of monomeric/short chain silicate species. Usually the... 

The ability of aluminium to adopt a wide variety of coordination numbers has led to the isolation of a large number of monomeric Al(III) hydroxide and organooxide complexes, many of which incorporate polyfunctional ligands, with the Group 13 metal centre in the coordination states 3-6. 

In the context of bidentate ligands, and in a similar vein to the polyfunctional aryloxides discussed above [141, 142, 146, 147], the chelation of a metal centre by deprotonated j5-diketones is a recurrent feature of monomeric organooxide complexes of aluminium. The employment of such ligands results in the observation of simple hexa-coordinate complexes which incorporate three [RC(0)C(H)C(0)R ] moieties (R = R = Me [177,178], CF3 [179], Ph [180, 181] R = f-Bu, R = CF3 [182]). More recently, the cocrystallisation of M(acac)3 (M = Al, Cr) has allowed the crystallographic study of metal disorder in a series of solid solutions of stoichiometry Ali, cCi x(acac)3 (x = 0.02-0.91) [183, 184]. Chelation of the metal centre similar to that reported in monomeric ] -diketonates has also been noted in the presence of... 

While the isolation of ClMeAl[2,6-(t-Bu)-OC6H3] from tert-butylamine has already been reported to result in the simple, monomeric mono-solvate [132], the incorporation of Group 17 elements as inter-aluminium bridges has been revealed in the (AlCl)2-based dimers [ArO(Me)Al(/r-Cl)]2 Ar = 2,6-(t-Bu)2-C6H3 [132], 2,6-(t-Bu)2-4-Me-C6H2 [129]. ... 

Aluminium tri-n-alkyls are dimeric in solution, although - especially for higher alkyls - the fraction of monomer can become significant at higher temperatures [ 19] in the gas phase they are usually monomeric. Kinetic evidence indicates that olefin insertion involves a monomeric aluminium trialkyl this suggests a Cossee-type insertion mechanism. Kinetic data do not indicate the presence of an intermediate olefin 7c-complex [23]. However, if the olefin complexation energy at the 7c-complex stage is low, this would be expected. 

Monomeric imides of aluminium, gallium and indium have been stabilised by installing extremely bulky groups on both the group 13 element and the... 

Four-coordinate, monomeric aluminium amides. Monomeric, four-coordinate aluminium amido derivatives are now quite numerous, yet none had been structurally characterized before 1980. They may be divided into two broad categories those which are Lewis base adducts and those in which four-coordination for aluminium is a result of complexation by a chelating ligand. 

Aluminium complexes of chelating amido ligands are perhaps the most common type of monomeric four-coordinate aluminium amide. A full listing of such complexes will not be provided and selected examples will suffice to illustrate synthetic approaches and... 

Higher coordinate monomeric aluminium amides. The distorted square pyramidal... 

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