Manganese complexes formation

However the Mn (aq) ion can be stabilised by using acid solutions or by complex formation it can be prepared by electrolytic oxidation of manganese(II) solutions. The alum CaMn(S04)2.12H2O contains... 

Ground-state electronic configuration is ls 2s 2p 3s 3p 3i 4s. Manganese compounds are known to exist in oxidation states ranging from —3 to +7 (Table 2). Both the lower and higher oxidation states are stabilized by complex formation. In its lower valence, manganese resembles its first row neighbors chromium and especially iron ia the Periodic Table. Commercially the most important valances are Mn, Mn ", or Mn ". ... 

When acetylthiophenes are subjected to orthomanganation, formation of the 2,3-, 103, and 3,4-, 104, metallocycles is observed [88JOM(349)197]. Complex 103 contains two coplanar live-membered heterocycles with octahedral manganese. Complex 104 is also planar. In both cases, substantial delocalization of the TT-electron density follows from the structural parameters. 

The rate of peroxide decomposition and the resultant rate of oxidation are markedly increased by the presence of ions of metals such as iron, copper, manganese, and cobalt [13]. This catalytic decomposition is based on a redox mechanism, as in Figure 15.2. Consequently, it is important to control and limit the amounts of metal impurities in raw rubber. The influence of antioxidants against these rubber poisons depends at least partially on a complex formation (chelation) of the damaging ion. In favor of this theory is the fact that simple chelating agents that have no aging-protective activity, like ethylene diamine tetracetic acid (EDTA), act as copper protectors. 

In contrast to the ionic complexes of sodium, potassium, calcium, magnesium, barium, and cadmium, the ease with which transition metal complexes are formed (high constant of complex formation) can partly be attributed to the suitably sized atomic radii of the corresponding metals. Incorporated into the space provided by the comparatively rigid phthalocyanine ring, these metals fit best. An unfavorable volume ratio between the space within the phthalocyanine ring and the inserted metal, as is the case with the manganese complex, results in a low complex stability. 

An interesting sequence, again overall an isomerization, is the stoichiometric formation of the manganese complexes 68, which, on basic alumina, isomerize to the allenyl complexes 69 from the latter the allenes 70 can be liberated with cerium(IV) ammonium nitrate (CAN) in good yields [128] (Scheme 1.30). 

The most direct evidence for surface precursor complex formation prior to electron transfer comes from a study of photoreduc-tive dissolution of iron oxide particles by citrate (37). Citrate adsorbs to iron oxide surface sites under dark conditions, but reduces surface sites at an appreciable rate only under illumination. Thus, citrate surface coverage can be measured in the dark, then correlated with rates of reductive dissolution under illumination. Results show that initial dissolution rates are directly related to the amount of surface bound citrate (37). Adsorption of calcium and phosphate has been found to inhibit reductive dissolution of manganese oxide by hydroquinone (33). The most likely explanation is that adsorbed calcium or phosphate molecules block inner-sphere complex formation between metal oxide surface sites and hydroquinone. 

An electrospray mass spectrometric study of the interaction of manganese(II) salts with the tetrathia analogue of cyclam showed the utility of this technique for detecting complex formation for both manganese and a series of other metal cations. 

In other work, solution complex formation of the pendant-arm ligands 1,4,10,13-tetraoxoa-7,16-diazacyclooctadecane-7-malonate and 1,4,10,13-tetraoxoa-7,16-diazacyclooctadecane-7,16-bis(malonate) has been investigated with a range of both transition and nontransition metal ions the 1 1 manganese(II) complexes of these species have been reported to show stabilities (log Ai values) of 7.41 and 5.60, respectively, in water (7=0.15, 25°C). 

The ease with which olefins form complexes with metals naturally led to investigation of acetylenes as ligands but until recent years only a few ill-defined, unstable acetylene complexes of copper and silver were known. Now complexes of acetylenes with metals of the chromium, manganese, iron, cobalt, nickel, and copper subgroups are known. These complexes fall naturally into two classes—those in which the structure of the acetylene is essentially retained and those in which the acetylene is changed into another ligand during complex formation. Complexes of the first class are discussed here and the second class is discussed in Section VI. 

The Mn(II)-catalysed oxidation of glucose by peroxodisulfate ions occurs via a radical-chain mechanism.26 Kinetics of oxidation of thiodiglycollic acid by (trans-cyclohexane-l,2-diaminc-/V, N, N, /V -tetraacetatolmanganateilJI) have been investigated.27 Oxidations of ketoses and aldoses by manganese(IV) in sulfuric acid media have a first-order dependence on sugar and fractional-order dependence on oxidant.28 A mechanism has been proposed for the oxidation of L-malic acid by Mn(III) pyrophosphate in aqueous acid, involving complex formation and radicals.29... 

The cerium(IV) oxidation of lactyllactic acid49 and of 4-oxopentanoic acid50 in aqueous nitric acid solutions shows first-order dependence of the reaction on both cerium(IV) and substrate. A 1 1 complex formation between manganese(III) and amine, which later decomposes in the rate-limiting step, best explains the kinetics of oxidation of aliphatic amines by cerium(IV) in nitric acid medium in the presence of manganese(II).51 The kinetics of oxidation of naphthalene, 2-methyhiaphthalene, and a-naphthol with cerium(IV) in perchloric acid solutions have been studied.52 Use of a 50-fold molar excess of cerium(IV) perchlorate results in complete oxidation of fluorophenols to CO2, HCO2H, and HF in 48 h at 50 °C.53... 

The mechanism of the epoxidation of alkenes by the cytochrome P450 model, sodium hypochlorite-manganese(III) tetraarylporphyrins, involves rate-determining formation of an active species 234 from a hypochlorite-manganese complex 233 (Scheme 6) pyridine or imidazole derivatives, as axial ligands, accelerate this step by electron donation, although the imidazoles are destroyed under the reaction conditions368. 

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