Cobalt spectral characteristics

The expanded cobalt(II) [Co(Me8tricosanesar)]2+ and cobalt(III) [Co(Me8tricosatrienesar)] + sarcophaginates have demonstrated usual sterically induced structural and spectral characteristics [151]. The Co-N distances in [Co(Me8tricosatrienesar)]s+ cation are remarkably... 

Figure 2 shows the ESDR spectra of cobalt complexes incorporated in SAP matrices. The sample with Cosalen is characterized by a shoulder at 45.103 cm l, absorption bands at 39.103, 26.103 and a shoulder at 19.103. After heating this sample at 115 C, an additional band appears at 31.5. 1Q3 cm l. The ESDR spectra of Cosalophen incorporated in SAP matrix shows bands of v max at 39.103, 29.103, 27.5.1()3, 25.103 and 21.6.103 cm-i. Heating (- 115 C) this sample does not lead to a change of the spectral characteristics. The behavior of the sample under heating indicates that most of the complex incorporated in SAP matrix is the cobalt compound exempt from molecular oxygen. 

The visible absorption spectrum of cobalt carboxypeptidase A was at an early stage thought to be characteristic of sulfur coordination (16, 105). The originally published spectrum (94) is poorly resolved (Fig. 14), but a more detailed study has recently been announced (106). Maxima at 555 nm (s — 160 M-1 cm-1) and 572 nm (e = 160 M-1 cm-1), a shoulder at 500 nm and a near-infrared band centered at 940 nm (e == 25 M-1 cm-1) are reported. There seems to be a clear resemblance with spectral forms... 

Recently, two papers have appeared reporting the spectral properties of cobalt alkaline phosphatase. According to Simpson and Vallee (115) addition of two equivalents of Co2+ to the apoenzyme yields only a small absorption increase around 500 nm, characteristic of octahedral complexes. Only slight activation is observed in this process. Further addition of two more equivalents of Co2+ results in full activation and in the formation of an intense visible absorption. Addition in excess of four equivalents has no further effect on activity or spectrum. 

Visible Reflection Spectra. The final calcination temperature of MoCo-124 samples has been varied in order to study its influence on the coordination of the cobalt ions. The reflection spectra are shown in Figure 1. The spectra of MoCo-124, calcined at 400 and 500°C show a broad absorption band, covering the whole spectral region, with a weak superposition of the characteristic triplet of cobalt aluminate. This indicates that the cobalt ions are for the greater part still on the catalyst surface and not in the alumina lattice. The spectra of the MoCo-124 samples, calcined at 650-700 °C show a strong increase in intensity of the triplet band, while the broad absorption band has disappeared. This indicates the formation of a cobalt aluminate phase. 

One method used to isolate a X-ray line from unwanted background and noise, employs equilibrated filters. It consists of linking the concentration of interest to the difference between two measurements. The first is obtained by installing a transmission filter between the sample and the detector to isolate the characteristic radiation of the element wanted and the second by fitting an absorption filter which is opaque to this same radiation. This will enable, for example, to quantify the copper from its main spectral line by using two filters, one made of nickel and the other made of cobalt. The fluorescence originating from the filters themselves is a limiting factor in this method, which is reserved for routine measurements. 

Electronic Structures of Co(ll) Compounds.12 As already noted, cobalt(n) occurs in a great variety of structural environments because of this the electronic structures and hence the spectral and magnetic properties of the ion are extremely varied. We shall try to mention here each of the principal situations, giving its chief spectral and magnetic characteristics and citing representative cases. 

The general features of the uptake of molecular oxygen by cobalt(II) complexes are reviewed. Two types of interac-tion are encountered those in which the Co. O stoichiometry is 1 1 and those (2 1) in which bridged complexes are formed. The thermodynamics and kinetics of oxygenation and the spectral, ESR, and structural characteristics of the products are discussed, and a comprehensive table of all characterized cobalt-02 carriers is included. A comparison is made of the cobalt(II)-02 interaction with the iron(II)-and copper(I)-02 systems occurring in the biologically important respiratory pigments. 

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