IV state

A number of organic compounds, eg, acetylacetone [123-54-6] and cupferron [135-20-6] form compounds with aqueous actinide ions (IV state for reagents mentioned) that can be extracted from aqueous solution by organic solvents (12). The chelate complexes are especially noteworthy and, among these, the ones formed with diketones, such as 3-(2-thiophenoyl)-l,l,l-trifluoroacetone [326-91-0] (C4H2SCOCH2COCF2), are of importance in separation procedures for plutonium. 

The EPA summary (4) of Title IV states the basics of the acid deposition control amendments ... 

Porphyrin complexes have been the most intensively studied macrocyclic complexes of these metals [129]. They are formed in a wide range of oxidation states (II-VI) and they are, therefore, treated together under this heading, though most of the chemistry for ruthenium lies in the II-IV states. Octaethylporphyrin (OEP) complexes are typical. 

The primary reason for studying aqueous plutonium photochemistry has been the scientific value. No other aqueous metal system has such a wide range of chemistry four oxidation states can co-exist (III, IV, V, and VI), and the Pu(IV) state can form polymer material. Cation charges on these species range from 1 to 4, and there are molecular as well as metallic ions. A wide variety of anion and chelating complex chemistry applies to the respective oxidation states. Finally, all of this aqueous plutonium chemistry could be affected by the absorption of light, and perhaps new plutonium species could be discovered by photon excitation. 

A predominant feature of the atomic structure of the lanthanide group is the sequential addition of 14 electrons to the 4f subshell (Table 1). The /"electrons do not participate in bond formation and in ordinary aqueous solutions all of the lanthanides exhibit a principal (III) state. The common (III) state confers a similarity in chemical properties to all lanthanide elements. Some of the lanthanides can also exist in the (II) state (Nd, Sm, Eu, Tm, Yh) or in the (IV) state (Ce, Pr, Nd, Tb, Dy). Except for Ce(IV), Eu(II), and Yb(II), these unusual lanthanide oxidation states can only be prepared under drastic redox pressure and temperature conditions, and they are not stable in aqueous solutions. Cerium (IV) is a strong oxidizing agent... 

Mononuclear ER4 and simple four-coordinate compounds of E(IV) states are the baseline for viewing the other coordination numbers, the effect of bulky ligands, bonds to other E or metals, E(II) compounds, multiple bonds and other phenomena discussed in later sections. Basic parameters for some simple compounds are presented in Table 1, taken from the gas-phase data summarized by Molloy and Zuckerman5 and Haaland6. These data show the unperturbed molecules in the gas phase and provide the base for... 

The chemistry of tellurium-containing heterocycles is a growth point in heterocyclic chemistry. The tendency for tellurium to take up the Te(IV) state, especially when bonded to oxygen or the halogens, has resulted in the synthesis of new types of heterocycles containing hypervalent tellurium. 

The apparent kinetics of proton-coupled ReV/in electron transfer also are dependent on 0X0 group geometry here (ks,h)cis/(ks,h)trans 100 [36]. It is proposed that the apparent kinetics is controlled by the thermodynamic accessibility of the intermediate Re (IV) state, whose effective potential is modulated by protonation, 0X0 group geometry, and pyridyl ligand substituents. 

One of the difficulties in characterizing the Cr(IV) state is that it is ESR silent, whereas the corresponding Cr(V) oxidation state (Section II,B) gives strong signals (24). 

The most common coordination number of titanium is six (recognized for all oxidation states of the metal), although compounds are known in which the coordination number is four, five, seven or eight. The common oxidation states of titanium with the associated coordination numbers and stereochemistries are summarized in Table 3. The properties of these molecules will be discussed in the appropriate sections. In brief, however, titanium compounds in the +III or lower oxidation states are readily oxidized to the +IV state. Furthermore, titanium compounds can usually be hydrolyzed to compounds containing Ti—O linkages. 

It is of interest to note that in his description of lead, Geber mentions that in calcination it does not preserve its proper weight hut is changed to a new weight. He ventures no explanation however as to the cause of this phenomenon. A later chemist, Eck of Sulzhach, supposed to have written about 1490, whose work Clavis Philosophortim was printed in the Theatrum Chemicum, Vol. IV, states more specifically,... 

In contrast to the situation a decade ago, many incomplete cubane-type clusters with Mo304 S cores have been prepared and the structures have been determined by X-ray structure analyses. The results obtained are summarized in Tables I—III. The formal oxidation state of molybdenum in the compounds cited here is in all cases IV. Unlike Mo(VI) and Mo(V) compounds, mononuclear oxo or dioxo compounds of the Mo(IV) state are relatively rare and all the incomplete cubane-type compounds cited here have no terminal oxo ligand. Three Mo atoms form an equilateral triangle, and three single bonds exist between each Mo. Except for the compounds 1, 8, and 31 (Table III), and excluding Mo—Mo bonds, each molybdenum is octahedrally coordinated. 

Equation III is merely stating that a correlation function of a periodic signal is also periodic while Equation IV states that the maximum amount of correlation of a periodic function occurs when the same point of that signal is compared with itself and that the correlation is diminished as one compares two points that are farther and farther apart (up to a difference of T). Equation V states that the autocorrelation function is symmetric about t = 0. 

It can be seen that the (111) state is highly stable with respect to disproportionation in aqueous solution and is extremely difficult to oxidize or reduce. There is evidence for the existence of the (II) state since tracer amounts of amencium have been reduced by sodium amalgam and precipitated with barium chloride or europium sulfate as earner. The (IV) state is very unstable in solution the potential for americium(III)-ameridum(IV) was determined by thermal measurements involving solid Am02. Amencium can be oxidized to the (V) or (VI) state with strong oxidizing agents, and the potential for the americium(V)-americium(Vl) couple was determined potentiometrically. 

Berkelium is known to exist 111 aqueous solution in two oxidation states, the (III) and the (IV) states, and the ionic species presumably correspond to Bk+3 and Bk+4. The oxidation potential for the berkelium(lll)-berkehum(IV) couple is about —1.6 V on the hydrogen scale (hydrogen-hydrogen ion couple taken as zero)... 

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