Manganese complexes electronic spectra

Higher Oxidation States of Manganese.—When XeFj is heated with Mnp2 at 120 °C for 60 h, wine-red XeMnFj is formed. Magnetic data suggest that this is a complex of The electronic spectrum of CsjMnF has been... 

Manganese(II) salts are characteristically very pale pink or colourless. For the Mn + ion in an octahedral high-spin complex, "d-d" transitions are both spin- and Laporte-forbidden (see Section 20.6). Although the electronic spectrum of [Mn(H20)g] + does contain several absorptions, they are all weaker by a factor of sslO than those arising from spin-allowed transitions of other first row metal ions. The weak absorptions observed for Mn + arise from promotion of an electron to give various excited states containing only three unpaired electrons. 

The usual ESR spectrum of manganese is characterized by the existence of six maxima. With our complexes, however, owing either to the screening produced by spins of nonparticipating electrons along the... 

While the stoichiometries of the Mn SOD enzymes appear to vary, the properties of the Mn-binding site do not. This is borne out in the electronic spectra of these proteins, which display a great degree of similarity despite the diversity of sources from which they have been isolated (Table II). This type of spectrum is distinctive for manganese in the trivalent oxidation state (3). The native enzymes are EPR silent, as might be anticipated if they contained Mn solely as the trivalent ion (S = 2) (1, 6,12,18-20, 24). However, when the enzymes are denatured, the characteristic six-line pattern of Mn(II) (I = 5/2) appears. Magnetic susceptibility studies with the E. coli SOD were consistent with the presence of a monomeric Mn(III) complex with a zero-field splitting of 1 to 2 cm-1 (4). The enzymes are additionally metal specific (however, see Refs. 36 and 37) metal reconstitution studies with E. coli and B. stearothermophilus revealed a strict requirement for Mn for superoxide dismutase activity (2, 22, 23). 

When manganese(iii) is mixed with the [VO(dtpa)] " ion in an acetate buffer medium, a reaction occurs to form a complex that retains the characteristic visible absorptions of Mn i and but slowly bleaches to Mn and V. The disappearance of and formation of Mn can also be detected by the e.s.r. spectrum. It is proposed that the initial product is the dinuclear complex (5), which slowly undergoes electron transfer and rearrangement to form (6). 

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