Trivalent metals

Tetravalent metals Trivalent metals Divalent metals ... 

In Fig. 26 we present the measured spectrum of the valence band and 4/region of SmB6, along with that of metallic, trivalent LaB6, obtained for comparison from surfaces prepared in UHV by abrasion with a diamond file. The LaB6 spectrum has been normalized to the same counting time as the SmB6. The rather low and almost featureless emission from the B(sp) and La(5d) states is apparent in Fig. 26. The... 

Fig. 26. XPS spectra of the valence band and 4/ region of mixed valence SmBg and of metallic trivalent LaBg.

As a fundamental class of compounds in the fields of synthetic solid-state (and also molecular) chemistry, cyanamides and carbodiimides have gained increasing attention within the past decade. Because of their 2-fold anionic charge, both cyanamide and carbodiimide structural units allow the realization of nitrogen-based pseudo-oxide chemistry since NCN is able to replace in a wide variety of novel materials. A number of alkali metal, alkaline-earth metal, main-group metal,divalent transition-metal, trivalent rare-earth metal,and also triva-lent transition-metal cyanamides/carbodiimides were obtained following different synthetic routes. The only carbodiimide containing divalent lanthanide ions was reported by DiSalvo et al., who found that EuNCN is isostructural to the already known a-SrNCN. ... 

The French chemist undoubtedly studied thallium in much greater detail than W. Crookes. He showed that the metal formed trivalent and monovalent compounds. Monovalent thallium has much in common with alkali metals trivalent thallium resembles aluminium. J. Dumas named it the paradoxical metal . It was the similarity of thallium with sodium and potassium that gave rise to the idea that thallium was a mixture of unknown alkali metals with large atomic masses. It is regrettable that all the credit for the discovery of thallium is given to W. Crookes, while the French chemist s significant achievements are often ignored. 

Aryls Alkyl Homogeneous Catalysis The Electronic Stmcture of the Lanthanides Variable Valency Solvento Complexes of the Lanthanide Ions Lanthanides Coordination Chemistry The Divalent State in Solid Rare Earth Metal Halides Lanthanides Comparison to 3d Metals Trivalent Chemistry Cyclopentadienyl Tetravalent Chemistry Organometallic Organic Synthesis. 

Because of the highly tunable properties of LDHs, it is possible to optimize their flame-retardant properties by adjusting many parameters, such as dispersibility, divalent metals, trivalent metals, and anions. Our aim in this section is to discuss recently published work on how these factors affect the flame retardancy of polymer/LDH nanocomposites. 

Fig. S. Cross section for the 4f shell in BIS, normalized to the CIs XPS cross section (Scofield 1976). Crosses represent the cross section per electron state (left scale), circles the total cross section (right scale). For the total cross sections of Tm and Yb metals trivalent configurations have been assumed for divalent configurations the total cross sections for Tm and Yb are 0.35 and 0, respectively.

This lanthanide Laves phase becomes ferromagnetic at Tc = 61 K under ambient conditions. The saturation hyperfine field and magnetically induced quadrupolar coupling correspond within the experimental errors to the free-ion values (see also fig. 37). Similarly, the isomer shift lies well inside the typieal range of metallic trivalent... 

Therefore, the critical intermediate in B 12-chemistry is a Co(III)-olefin 7t-complex. The formation of this intermediate is chemically reasonable because an enol is an electron-rich species whereas a metal (trivalent Co) is electron deficient. 

The A//298 WrtS calculated to be 196.23 1.26 kjmol , and AS298 was derived to be 80.54 JK mol . The estimated boiling point for the metal is 1745 K. Nugent et al. [81] had estimated the heat of sublimation to be 163 kJ mol and David et al. [82] had predicted a value of 197 kJmol . The vapor pressure of californium metal is intermediate between that of samarium metal (trivalent) and of europium metal (divalent) [80]. The data show that the californium metal was clearly trivalent up to 1026 K, and that it is one of the most volatile actinide metals. Its high volatility precludes bulk vaporization studies above 1073 K by the Knudsen technique. No evidence by mass spectrometry was obtained in this latter work for the presence of CfO. 

Among the reported lanthanide monoxides, only EuO is well-characterized, impure YbO can be prepared with difficulty, and metallic (trivalent) monoxides of La, Ce, Pr, Nd, and Sm can be synthesized at high temperature and pressure. Earlier reports of lanthanide monoxides as surface phases are believed to be oxynitrides, oxycarbides, or hydrides [40]. Similarly, earlier reports of PuO are now believed to have been an oxide carbide [97]. 

First, the use of water limits the choice of Lewis-acid catalysts. The most active Lewis acids such as BFj, TiQ4 and AlClj react violently with water and cannot be used However, bivalent transition metal ions and trivalent lanthanide ions have proven to be active catalysts in aqueous solution for other organic reactions and are anticipated to be good candidates for the catalysis of aqueous Diels-Alder reactions. 

Masking by oxidation or reduction of a metal ion to a state which does not react with EDTA is occasionally of value. For example, Fe(III) (log K- y 24.23) in acidic media may be reduced to Fe(II) (log K-yyy = 14.33) by ascorbic acid in this state iron does not interfere in the titration of some trivalent and tetravalent ions in strong acidic medium (pH 0 to 2). Similarly, Hg(II) can be reduced to the metal. In favorable conditions, Cr(III) may be oxidized by alkaline peroxide to chromate which does not complex with EDTA. 

Description of the Method. The operational definition of water hardness is the total concentration of cations in a sample capable of forming insoluble complexes with soap. Although most divalent and trivalent metal ions contribute to hardness, the most important are Ca + and Mg +. Hardness is determined by titrating with EDTA at a buffered pH of 10. Eriochrome Black T or calmagite is used as a visual indicator. Hardness is reported in parts per million CaCOs. 

The site preference of several transition-metal ions is discussed in References 4 and 24. The occupation of the sites is usually denoted by placing the cations on B-sites in stmcture formulas between brackets. There are three types of spinels normal spinels where the A-sites have all divalent cations and the B-sites all trivalent cations, eg, Zn-ferrite, [Fe ]04j inverse spinels where all the divalent cations are in B-sites and trivalent ions are distributed over A- and B-sites, eg, Ni-ferrite, Fe Fe ]04 and mixed spinels where both divalent and trivalent cations are distributed over both types of sites,... 

The inorganic flocculating agents are water-soluble salts of divalent or trivalent metals. For all practical purposes these metals are aluminum, iron, and calcium. Sodium siHcate is also used in some appHcations. The principal materials currently in use are described in the foUowing. 

The usual valence of indium is three, although monovalent and bivalent compounds of indium with oxygen, halogens, and Group 15 (VA) and 16 (VIA) elements ate well known. The lower valence compounds tend to disproportionate into the trivalent compound and indium metal the trivalent compounds ate stable. 

The arc and spark spectra of the individual lanthanides are exceedingly complex. Thousands of emission lines are observed. For the trivalent rare-earth ions in soUds, the absorption spectra are much better understood. However, the crystal fields of the neighboring atoms remove the degeneracy of some states and several levels exist where only one did before. Many of these crystal field levels exist very close to a base level. As the soUd is heated, a number of the lower levels become occupied. Some physical properties of rare-earth metals are thus very sensitive to temperature (7). 

In seawater—dolime and hrine—dolime processes, calcined dolomite or dolime, CaO MgO, is used as a raw material (Table 9). Dolime typically contains 58% CaO, 41% MgO, and less than 1% combined Si02, P O, and CO2 where R is a trivalent metal ion, eg, Al " or Fe " ( 4). Roughly one-half of the magnesia is provided by the magnesium salts in the seawater or brine and the other half is from dolime (75). Plant size is thus reduced using dolime and production cost is probably lower. 

Phosphoms haUdes and metals or metal salts form addition complexes. Some typical compounds are PCl iSbCl and PCl iAlCl. The trivalent complexes contain metal—phosphoms bonds. The pentavalent complexes involve rearrangements to produce assembles of tetrahedral PX cations and various anions. 

Similar coordination occurs also in the presence of other di- and trivalent metals. Reduction of the double bonds can produce various hexenoic acid mixtures. 

A mixture of dimethyl sulfate with SO is probably dimethyl pyrosulfate [10506-59-9] CH2OSO2OSO2OCH2, and, with chlorobenzene, it yields the 4,4 -dichlorodiphenylsulfone (153). Trivalent rare earths can be separated by a slow release of acid into a solution of rare earth chelated with an ethylenediaminetetraacetic acid agent and iodate anion. As dimethyl sulfate slowly hydrolyzes and pH decreases, each metal is released from the chelate in turn and precipitates as the iodate, resulting in improved separations (154). 

Unlike boron, aluminum, gallium, and indium, thallium exists in both stable univalent (thaHous) and trivalent (thaUic) forms. There are numerous thaHous compounds, which are usually more stable than the corresponding thaUic compounds. The thaUium(I) ion resembles the alkaU metal ions and the silver ion in properties. In this respect, it forms a soluble, strongly basic hydroxide and a soluble carbonate, oxide, and cyanide like the alkaU metal ions. However, like the silver ion, it forms a very soluble fluoride, but the other haUdes are insoluble. Thallium (ITT) ion resembles aluminum, gallium, and indium ions in properties. 

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