Of tris-diamine cobalt III

The circular dichroism spectra in the region of the first absorption band of the tris-bidentate complex ions having six-membered chelate rings sure known to be particularly sensitive to experimental conditions. For example, the CD spectrum of A-lel -[Co(R,R-ptn) ]C1, in an aqueous solution shows two peaks A = -O.589, 522 nm A = - 0.104, 462.5 nm, whereas that of A-lel,-[Co(R,R-ptn) ](CIO,) in an aqueous solution gives a negative peak (A , = -O.587T at 518 nm (41). The solid state CD differ from the solution CD and the solution CD are sensitive to the temperature of measurement and are affected by the presence of oxo anions (42, 43, 44). Table V lists the lowest frequency CD spectra of tris-diamine cobalt(III) complexes in the CT region. 

Using all of the recorded CD data for tris-diamine cobalt-(III) complexes of known absolute configuration, an empirical rule relating the absolute configuration to CD spectra of tris-diamine cobalt(III) complexes in the charge-transfer region was estab-... 

Table V The lowest frequency CD band of tris-diamine cobalt(III) complexes in the CT region...

Circular Dichroism Spectra of Tris(diamine)cobalt(III) Complexes... 

The following procedure is based on the reaction of an aqueous solution of cobalt(II) chloride with the equivalent amount of (2-aminoethyl)carbamic acid, followed by oxidation with hydrogen peroxide and the subsequent formation of bis(ethylene-diamine)cobalt(III) ions. The bis(ethylenediamine)cobalt(lII) species are converted to the carbonato complex by reaction with lithium hydroxide and carbon dioxide. During the entire preparation a vigorous stream of carbon dioxide is bubbled through the reaction mixture. This procedure appears to be essential in order to minimize the formation of tris(ethylenediamine)cobalt(III) chloride as a by-product. However, the formation of a negligible amount of the tris salt cannot be avoided. The crude salts have a purity suitable for preparative purposes. The pure salts are obtained by recrystallization from aqueous solution. 

By far the tris-type complexes such as tris(diamine)cobalt(III), tris(dicarboxylato)-cobaltate(III), and tris(p-ketoacidato)cobalt(III) are best preparwi by oxidizing the cobalt(II) ion in the presence of the ligand in basic form. However, Bauer and Drinkard utilized sodiiun tricarbonatocobaltate(III) trihydrate in a general method to prepare ... 

In the first study of this sort 29) Keller and Edwards sought to prepare tris(A -hydroxyethylethylenediamine)cobalt(III) and to examine the reactivity of the uncoordinated hydroxy group. They reported such groups to be completely inert in the material they prepared. A subsequent study 15) reported that the oxidation of a basic mixture of a cobalt(II) salt and AT-hydroxyethylethylenediamine produced primarily tris(ethylene-diamine)cobalt(III). In this latter study, a method for preparing complexes of AT-hydroxyethylethylenediamine (hereafter abbreviated as etolen) was developed based upon reactions of the type ... 

Diamines. Chromatography has been used to isolate three isomers of trans- and cis-[Co(CN)2 (RR)-cyclohexane-l,2-diamine 2] and five isomers of the corresponding propylenediamine complexes. Mer- and /ac-isomers of tris(meso-pentane-3,4-diamine)cobalt(iii) have been prepared and separated using column chromatography. The rates of aquation of three isomers of [CoCl(tmd)(dien)] and one isomer of [CoCl(tmdXdpt)] have been measured and the kinetic parameters calculated [dpt = NH2(CH2)3NH(CH2)3NH2, tmd = NH2(CH2)3NH2]. The interaction of [Co(dien)2] with sulphate, thiosulphate, sulphite, selenite, tellurite, and carbonate ions has been studied potentiometrically and stability constants determined for the outer-sphere complexes. The i.r. spectrum of octahedral... 

Although tris(aminoacidato)cobalt(III) complexes, [Co(ama)3], are electrically neutral, they can be regarded either as complex cations or as complex anions because they can anchor complex anions or complex cations with N-H - O type hydrogen bonds along the C3 or the C2 axis. Therefore they may be expected to be resolvable either by chiral complex anions or by complex cations. We here describe the optical resolution of some [Co(ama)3] using A-[Co(sep)] + and A-[Co(chxn)3] + (chxn = cyclohexane-diamine) as chiral selectors. The procedure is almost the same as described in the preceeding section. 

The two cobalt(III) hexaamines with relatively short metal-donor distances considered here are [Co(7ra s-diammac)]3+ trans-diammac is trans-1,4,8,11 -tetraazacy-clotetradecane-6,13-diamine, see Fig. 17.11.1) and [Co(trap)2]3+ (trap is 1,2,3-tri-aminopropane, see Fig. 17.11.2). There are three conformers of [Co(taa s-di-ammac)]3+ (35, 51,15 where 5 and 1 refer to the conformation of the five-mem-bered chelate rings in the complex - see also Section 17.3). The A<5-conformer is the most stable form and has been characterized by an X-ray diffraction study. 15-[Co(fra .v-diammac)]3+ has very short Co-N bonds (1.937A (four equatorial bonds), 1.946 A (two axial bonds)), and the experimentally determined high ligand field and the strongly negative redox potential confirm that these structural features are conserved in solution190 231,2811. 

The negative DCD peak for the [Co(sep)]2+...(i-, Z-tart -, and [Sb2(tart)2]2- associates is indicative of the anion association along the C2 axis. The change in the association mode, compared with nonmacrocyclic cobalt(III) tris-diaminates, is stipulated by the presence of the capping groups in the clathrochelate [Co(sep)] + cation that screen trigonal Ns-bases of the CoNe coordination polyhedron. 

Within the tris-chelate type of chiral coordination compound, the most extensively studied are the series of diamine chelates of cobalt(III), containing the octahedral [Cot )N6] cluster. The principal d—d transition of interest for the optical activity of these complexes is the Aj -> Tj octahedral excitation near 465 nm (Fig. 2), made up of the three single-orbital promotions, dxy dx -y , and the analogues obtained by the cyclic permutations of the electronic coordinates. The leading moments of the one-electron transition, dxy - , are the z-component of a magnetic dipole... 

In the dihedral tris-diamine complexes of cobalt(III) the upper state of the octahedral Ai - Ti d—d transition is broken down into components with Aj and... 

Such a steric distribution of the alkyl substituents raises the question whether stereoselectivity would be found in the tris complex with an L-amino acid forming chelate rings much less puckered than the 1,2-diamine chelate rings. The stereoselectivity in tris(L- or D-amino-acidato)cobalt(III) has been mainly studied for the elucidation of the steric interactions between the substituents on the a-carbon atom of the ligand. 

Using cobalt(II) as template, the trans compoimd [Co(L15)](C104)2 can be obtain (220, 223]. Cobalt(III) appeared to be non-effective in syntheses of this type, presimiably because of formation of non-labile diamine complexes. The effectiveness of platinum(n) and palladium(II) as templates is reduced markedly compared to nickel(II) and copper(II) for the same reason [220]. Tris(ethylenediamine) iron(II) interacts with acetone in the presence of atmospheric oxygen according to Equation (2.113). 

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