Manganese complexes, divalent

In iV-confused porphyrins, this agostic coordination mode has been observed frequently. To date, monomeric complexes of this macrocycle with divalent manganese (35, 26), divalent iron (36, 29), lanthanides (57), rhodium carbonyl (55), and group 12 elements (34), have been structurally characterized that exhibit this peculiar type of metal binding. A generic structure for several of... 

The ESR spectrum of Mn in sodium azide [28] shows a remarkable similarity to that of Mn in sodium chloride. In both cases the divalent manganese ion is located substitutionally at a monovalent sodium ion site, and the extra positive charge is compensated by a cation vacancy. The same mobility and coagulation effects are seen for both materials, and multiple sets of Mn —cation vacancy complexes are also observed. Vacancy hopping, which produces lifetime broadening of the resonance lines, is observed in NaNa (as well as in potassium and rubidium azides). As mentioned earlier. Miller and King [13] used the ESR spectrum of Mn " to observe the phase transition at 19°C. 

Peroxidase forms a number of complexes with hydrogen peroxide. The activation mechanism of substrate molecules in the active center of peroxidase involves the formation of a ternary complex heme-H20-donor of electrons. The role of the iron ion consists of transferring electrons from the donor to the hydrogen peroxide molecule. Peroxidase is endowed, moreover, with the oxidase function which increases in the presence of divalent manganese ions. 

The solution chemistry of manganese is relatively simple. The aquo-ion is resistant to oxidation in acidic or neutral solutions. It does not begin to hydrolyze until pH 10, and therefore free Mn " " can be present in neutral solutions at relatively high concentrations. Divalent manganese is a 3d ion and typically forms high-spin complexes lacking... 

Narang, K. K. et al., Synth. React, lnorg. Met.-Org. Chem., 1996, 26(4), 573 The explosive properties of a series of 5 amminecobalt(III) azides were examined in detail. Compounds were hexaamminecobalt triazide, pentaammineazidocobalt diazide, cis- and fram-tetraamminediazidocobalt azide, triamminecobalt triazide [1], A variety of hydrazine complexed azides and chloroazides of divalent metals have been prepared. Those of iron, manganese and copper could not be isolated cobalt, nickel, cadmium and zinc gave products stable at room temperature but more or less explosive on heating [2],... 

Many compounds of technetium and rhenium are of analogous composition and of corresponding physical and chemical properties. Because of the very similar ionic radii, isotypic crystal structure formation of analogous compounds could often be observed. Technetium remarkably differs from manganese by the high stability of pertechnetate compared with permanganate. Moreover, divalent technetium does not exist as a hydrated ion but only as a stabilized complex. 

Other than in prokaryotic cells which lack mitochondria and chloroplasts, manganese superoxide dismutases are apparently restricted to the above two organelles in eukaryotic cells (51, 52) this forms strong support for the symbiotic hypothesis for the origin of mitochondria and chloroplasts (53, 54). Kinetic studies of superoxide dismutation by these enzymes indicate three oxidation states of Mn (presumably divalent, trivalent, and tetravalent) are involved in the catalytic cycle (57, 58). They also show that a Mn-02 complex may conceivably be formed. Well-characterized Mn-dioxygen (i.e., 02,02 , 022 ) adducts are extremely rare, the first structurally characterized example being reported only in 1987 (60). 

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