Variable oxidation states

Variable oxidation state is also exhibited in the oxides themselves among metals in this region of electronegativity. Thus lead, for example, forms the monoxide PbO (+2) and the dioxide PbO 2 ( + 4) (the compound Pbj04 is not a simple oxide but is sometimes called a compound oxide). Similarly, manganese gives the oxides MnO and Mn02-... 

The more noble metals (for example copper, mercury and silver) can form oxides, and exhibit variable oxidation state in such compounds (for example CU2O, CuO), but it is not easy to prepare such oxides by direct action of oxygen on the metal, and elevated temperatures are necessary. Moreover, in the case of silver and mercury, loss of oxygen from the oxide by heating is easy. The oxidesare, however, basic (for example Ag20 - Ag, CuO - Cu in acids). 

However, if heated hydrogen chloride is passed over heated metals, the chloride is formed in the case of a metal exhibiting variable oxidation state, the lower chloride is obtained ... 

Variable oxidation state - One obvious feature of transition-metal chemistry is the occurrence of a number of characteristic oxidation states for a particular metal... 

The d Orbitals, Covalent Character and Variable Oxidation States - A Summary... 

Metal oxides of variable oxidation state as supports or support modifiers [202] are well known in gold catalysis. In the previous section we have already indicated some metal-support interactions influencing the electronic state of gold nanoparticles as well as the metallic or ionic state of gold. Of the numerous literatures we have to mention Haruta and Date [169], Bond [195], as well as Goodman works [186,203]. Further results can be found on the iron oxide system in recent literatures [162,204]. 

It can be assumed a priori [11] that the reason for the variable composition of the octachloroditechnetates may be either a variable oxidation state of technetium or substitution of some of the cations by H30+ ions. The first explanation was proposed [22], when the accuracy ( + 0.017 A) of the X-ray diffraction study by a photomethod [81] precluded the determination of the fine difference between the Tc-Tc distances in the [Tc2CI8]3- and [Tc2Cl8]2- anions, which is 0.03 A according to the latest X-ray diffraction data [11,35,60,63,82] (Table 1). An attempt was made [11] to determine the H30+ ions in potassium octachloroditechnetate, which led to their detection from the weak characteristic absorption lines in the infrared spectra (v OH) = 2965,2930, and 2865 cm-1 <5(HOH) = 1610 cm-1 [83,84]). The results [11] did not conflict with the revised X-ray diffraction data [82] according to which the K+ ions in the unit cell of potassium octachloroditechnetate (+ 2.5) are present in two non-equivalent positions sixfold (K ) and threefold (K") under these conditions, the sixfold positions were fully occupied by K+ ions, while the threefold positions were half-occupied. 

Their variable oxidation states and spin states. 

Manganese represents the epitome of that characteristic property of the transition element namely the variable oxidation state. The aqueous solution chemistry includes all oxidation states from Mn(II) to Mn(VII), although these are of varying stability. Recently attention has been focused on polynuclear manganese complexes as models for the cluster of four manganese atoms which in conjunction with the donor side of Photosystem(II) is believed involved in plant photosynthetic oxidation of water. The Mn4 aggregate cycles between 6 distinct oxidation levels involving Mn(II) to Mn(IV). 

Note that there are a number of different methods for indicating the oxidation state of a metal ion, especially transition metal ions that have variable oxidation states. As an example, the iron ion in its +2 oxidation state may be written as Fe +, Fe(II), Fe , or iron(ll). In this text, the methods are used interchangeably. 

Another reason that transition metals are good catalysts may be because they have variable oxidation states. Again, this allows the transition metal to provide an alternative reaction pathway with a lower activation energy, so speeding up the reaction. 

Transition metals act as catalysts because they have d orbitals available to form intermediate complexes with reactant molecules and because they have variable oxidation states. 

Other metah—a classification given to seven metals that do not fit the characteristics of transition metals. They do not exhibit variable oxidation states, and their valence electrons are found only on the outer shell. They are aluminum, gallium, indium, tin, thallium, lead, and bismuth. 

Characteristics that complicate the interpretation of geochemical and radiometric data for uranium deposits include 1) variable oxidation state of uranium and associated elements 2) the variety of aqueous species possible 3) the tendency for soluble uranium and... 

The majority of inorganic systems reported to exhibit photochromism are solids, examples being alkali and alkaline earth halides and oxides, titanates, mercuric chloride and silver halides.184 185 The coloration is generally believed to result from the trapping of electrons or holes by crystal lattice defects. Alternatively, if the sample crystal is doped with an impurity capable of existing in variable oxidation states (i.e. iron or molybdenum), an electron transfer mechanism is possible. 

We have already seen that imines may be formed by the oxidative dehydrogenation of co-ordinated amines and that this is a commonly observed process, particularly in macrocyclic systems. Likely mechanisms for these dehydrogenations were suggested in Chapter 5, which emphasised the role of the variable oxidation state metal ions in the process. These reactions are quite general and many examples involving iron or ruthenium complexes have been studied in detail. 

Variable Oxidation States of Iron in the Crystal Structure of Smectite Clay Minerals... 

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