Transition manganese oxide structures

Manganese Oxide Hydroxides, IV. The Buserite Group Structure Stabilized by Transition Elements, Chimia 1975, 29, 517-520. 

There are two examples of transition metal oxides forming ordered microporous materials (1) manganese oxide and (2) molybdenum vanadium mixed oxide, both of which contain MOg octahedra as the basic structural units to form one-dimensional channel pores. 

The first ordered microporous transition metal oxides were microporous manganese oxides, known as octahedral molecular sieves (OMS). The manganese oxide OMS are classified into three families the pyrolusite-ramsdellite family with a (1 x n) channel structure the hollandite-romanechite family with a (2 x n) channel structure ... 

Another example of the hollandite-type manganese oxides is Ki.5(H30)x MngOi6 [131, 132], where the HsO groups occupy part of the 1/4 vacant sites in the tunnels, not occupied by potassium ions. These groups intercalate into the structure during a hydrothermal synthesis. From susceptibility measurements, three phase transitions were observed [131, 132] at Ti = 180-250 K, Tj = 52 K, and T3 =... 

An intercalation process under reflux conditions for 4 days has been performed by Ma et al. to prepare chromium oxide-pillared manganese oxides [38]. In this reaction chromium hydroxyl acetate clusters, Cr3(OAc)7(OH)2, are used as the pillaring species. Cr + self-polymerizes under reflux to form polynuclear clusters between the manganese oxide layers. Intercalation of this trinuclear chromium complex constitutes a challenge because redox reactions may occur between manganese oxide and the transition metal oxide during the process, which could destroy the layer structure. 

The second class of sol-gels contains redox-active metal oxides, such as tungsten oxide, vanadium pentoxide, manganese oxide, and other transition metal oxides. Moreover, many n-type semiconductors such as zinc oxide, barium titanate, and titanium dioxide can be used in this class (113). The structures of these gels are sensitive to the pH and oxidation state of the precursors. Many redox-active sol-gels exhibit electrochromism (different oxidation states exhibit different colors, allowing spectroscopic determination of redox states). These gels can also accommodate the reductive insertion of lithium and other moieties. 

Several metal oxides with varying phase structures and nanostructures have been developed, including manganese oxide, iron oxide, molybdenum oxide, tin oxide, and titanium oxide. The most prominent issues surrounding transition metal oxide development efforts are (1) limited electronic conductivity and low theoretical capacitance in comparison to ruthenium oxide and (2) poor cyclability due to their redox nature and electrochemical instabilities. The varying electrochemically stable potential windows for some species of metal oxides completely eliminate their potential applications in ES devices. 

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