Spectral and Magnetic Studies

Grind purest ammonium iron(II) sulphate into a fine powder and measure its magnetic moment by the Evans method (Sec.2.1.3). 

Prepare 0.03 M solution of potassium hexacyanoferrate(II) and dilute 25.0 cm to 250 cm. Record the spectrum in a 2 cm cell between 800 and 300 nm. Dilute 10 cm of the soluticHi to 100 cm and record the spectrum between 300 and 250 nm. Dilute an aliquot of the latter solution 10-fold and record the spectrum at the shorter wavelengths. Compare these spectra with the previous spectrum. 

High spin octahedral iron(III) complexes have a (t2g) (eg) configuration and their magnetic moment shows 5 unpaired electrons. Their d-d spectra, like those of Mn(II) have very weak bands. However, low spin complexes eg hexacyanoferrate(III) have one unpaired electron. Its absorption spectrum shows that its d-d bands are superimposed on charge transfer bands. 

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Holm, R. H. Spectral and magnetic studies of substituted Ni(II) salicylaldimine complexes, in Advances in the Chemistry of the Coordination Compounds, Kirschner, S. (ed.). Macmillan New York, 1961. 

In 1961, Cotton and Fadder 43) further found that Ni(acac)2 exists in a monomer-trimer equilibrium in diphenylmethane over a 80—200 °C range. At low temperatures the green octahedrally coordinated trimeric species predominates, but at 200 °C the monomeric, square planar nickel complex is stable giving a red solution. Other /9-diketonate-nickel(II) complexes found to participate in a monomeric-trimer equilibrium from spectral and magnetic studies were... 

In this section we outline briefly the spectral and magnetic properties of complexes of the metals of Table 5. These are the properties that enable the stereo-chemical and electronic structures of metal complexes to be determined in solution and, hence in a biological environment. A study of these properties will be necessary to understand the nature of the interaction of the anti-tumour compounds with biological systems. 

In this section spectral and magnetic data on selected nickel(II) complexes are presented. The purpose of this section is that of showing some of the most relevant spectromagnetic studies on nickel(II) complexes. Particular emphasis will be given to work where a correlation between the properties and the electronic structure of nickel(II) complexes has been investigated. Much information is to be found in the tables, albeit without any detailed comment. 

The most important aspect of the study of Co(II) metalloenzymes is the possibility of using the metal ion as a functional, built-in reporter of the dynamics of the active site. The spectral and magnetic properties of Co (II) carbonic anhydrase have given valuable clues to the catalytic function of this enzyme. The recent studies of Co(II) alkaline phosphatase and Co (II) carboxypeptidase A indicate the general applicability of this approach to enzymes where the probe properties of the constitutive metal ion are poor. The comparison of the absorption spectra of these enzymes and low-molecular weight models have shown that the proteins provide irregular, and in some cases nearly tetrahedral environments. It is obvious, however, that a knowledge of the crystal structures of the enzymes is necessary before the full potential of this method can be exploited. 

Cor several years my coworkers and I have been studying the electronic absorption spectra of models for metal proteins and, in certain cases, of the proteins themselves. In favorable cases, additional information has been gathered from infrared spectral and magnetic susceptibility measurements. 

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