Trivalent Compounds

Compounds (2, M=As or Sb) and (Me3Si)2CHMCl2 were obtained from appropriate ratios of MCI3 and (Me3Si)2CHLi. 

In the solid state, PhaSbOAc has a distorted trigonal bipyramidal structure phenyl groups and lone-pair equatorial with bonded oxygen (Sb-O 213.7) and bridging oxygen (Sb-O 259.2, 251.3) axial. In solution the aggregation breaks down.  

Dipole moments of (p-RCeHJAsYa (Y = C1 or OR ) were measured changes in R (R = N02, Br, H, or Me) influenced neither the dipole moment of the Caryl—As(OR)2 Unit nor the conformation. Dibasic carboxylic acids, e.g., malonic and oxalic, cleave two Ph-Bi bonds in PhgBi. 

Electrochemical reductions of RSbIa (R=Pr or Bu) to (RSb)n occur in a variety of media. Other Sb-Sb bonded compounds are obtained from reaction of Mg with R2SbBr and RSbBrj (R=Pr or Bu).  

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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. 

Tri- and pentacoordinate phosphoms compounds often react by electron-pair mechanisms as demonstrated by the nucleophilic reactivity of the lone pair electrons in trivalent compounds, and the electrophilicity of the phosphoms atom in the pentavalent compounds. Some compounds also react by free-radical mechanisms. The theoretical and synthetic aspects of the chemistry of phosphoms compounds have been described (6—9). 

The secondary trivalent compounds manufactured ia quantity are chrome acetate, chrome nitrate, basic chrome chloride, basic chrome sulfate, and chrome oxide. 

Prolonged contact with certain chromium compounds may produce allergic reactions and dermatitis in some individuals (114). The initial response is usually caused by exposure to Cr(VI) compounds, but once the allergy is estabUshed, it is extended to the trivalent compounds (111,115). There is also limited evidence of possible chromium associated occupational asthma, but there is insufficient data to estimate a dose for assumed chromium-induced asthma. Reference 116 provides a summary and discussion of chromium hypersensitivity. 

Despite the above similarities, many differences between the members of this triad are also to be noted. Reduction of a trivalent compound, which yields a divalent compound in the case of cobalt, rarely does so for the heavier elements where the metal, univalent compounds, or hydrido complexes are the more usual products. Rhodium forms the quite stable, yellow [Rh(H20)6] " ion when hydrous Rh203 is dissolved in mineral acid, and it occurs in the solid state in salts such as the perchlorate, sulfate and alums. [Ir(H20)6] + is less readily obtained but has been shown to occur in solutions of in cone HCIO4. 

The toxicity of arsenicals conforms to the following order, from greatest to least toxicity arsines > inorganic arsenites > organic trivalent compounds (arsenoxides) > inorganic arsenates > organic pentavalent compounds > arsonium compounds > elemental arsenic. 

Bodner, G.M., Gagnon, C., and Whittern, D.N., A Fourier transform carbon-13 NMR study of trivalent compounds of phosphorus, arsenic, antimony and bismuth, and their LNi(CO)3 complexes, J. Organomet. Chem., 243, 305, 1983. 

Adiabatic detachment energy [7]. Abbreviations used rcoy (Em) = covalent radius of element E in a trivalent compound BE(E-E) = bond enthalpy of a single E-E bond D°298(E2) = dissociation enthalpy of the E2 molecule at standard conditions IE = ionization enthalpy EA = electron affinity AHf°(E2 g) = standard enthalpy of formation of the gaseous E2 molecule. 

Europium has been characterized by several workers (3, 13) as divalent in the metallic state. This is again borne out by the isomer shift of the metal, which is clearly much closer to that of the covalent divalent compounds than that of the covalent trivalent compounds. (The comparison should be made with covalent compounds because in the metallic state the atoms are bonded together by sharing the valence electrons.)... 

GaUium is truly an exotic element in that it has so many unusual characteristics. It can form fflonovalent and divalent as weU as trivalent compounds. It is considered a post-transitional metal that is more hke aluminum than the other elements in group 13. It has few similar characteristics to the two elements just below it in group 13 (In and Ti). 

The elements in the lanthanide series are soft, silver-like metals that mosdy form trivalent compounds. As metals, they are reactive, they tarnish when exposed to the atmosphere, and they react with most nonmetals when heated. Europium QgEr) is the most reactive. The sizes of the elements do not increase much when moving from left to right, but the hardness of the elements does increase. 

As an element, neodymium is a soft silver-yellow metal. It is malleable and ductile. It can be cut with a knife, machined, and formed into rods, sheets, powder, or ingots. Neodymium can form trivalent compounds (salts) that exhibit reddish or violet-like colors. 

This is especially true for trivalent compounds for which no clear correlation pattern could be found. When the signs are considered (these changes being more sensitive in P111 compounds as suggested in 1966, 1) it is then possible to highlight the importance of geometrical factors as will now be exemplified. 

Bismuth forms trivalent and pentavalent compounds. The trivalent compounds are more common. Many of its chemical properties are similar to other elements in its group namely, arsenic and antimony. 

Zirconium exhibits quadrivalency in most of its compounds although divalent and trivalent compounds also exist. Zirconium reacts with oxygen to form zirconium oxide, Zr02. In powder form, Zr metal ignites spontaneously forming oxide. Solid metal, however, is stable in air at ordinary temperatures, but reacts slowly at 200°C. Reaction is rapid at high temperatures. 

Trivalent Compounds.—In trivalent vanadium compounds the basic character of the element is well developed, and both normal and oxy-salts of the sesquioxide V203 are well defined, e.g. vanadous sulphate, V2(S04)3, and vanadium oxymonochloride, VOC1. It has been previously mentioned that resemblances between the elements of the A and B Subdivisions of Group V. are mainly restricted to the pentavalent compounds it is of interest to note that the oxychloride has analogues in the trivalent antimony and bismuth basic chlorides, SbOCl and BiOCl. Trivalent vanadium also displays considerable analogy, however, with other trivalent transitional elements, as shown by the following —... 

In these compounds the metal-carbon bonds are highly covalent and chemically rather stable. The chemical reactivity of the trivalent compounds, in particular those of the type R3M is associated with an easy oxidizability to the pentavalent state rather than with rupture of metal-carbon bonds. Thus, the vigorous reaction of the trialkyl compounds R3M with air depends on the following oxidative transformation ... 

But we have not told you the whole story about BF3. Boron is in group 3 and thus has only six electrons around it in its trivalent compounds. A molecule of BF3 is planar with an empty p orbital. This is the reverse of a lone pair. An empty orbital on an atom does not repel electron-rich areas of other molecules and so the oxygen atom of acetone is attracted electrostatically to the partial positive charge and one of the lone pairs on oxygen can form a bonding interaction with the empty orbital. We shall develop these ideas in the next section. 

All TiCl4- or VCl4-based catalyst systems studied showed highest polymerization activity if these compounds were reduced to the trivalent state. Reduction to a lower valence is always accompanied by a decrease in rate of polymerization, which indicates that the main catalytic activity of these catalyst systems is directly connected with the trivalent compounds. 

An interesting type of trivalent compound is CpM(7j4-diene)X2 (18-B-IX) X = Cl, Me, and triflate which can be prepared from CpMCLt and two equivalents of methylated allyl Grignard reagents in THF. In the presence of methylaluminoxane (MAO), these compounds polymerize ethylene85 similarly to the Ti analogues (Section 17-A-5). 

There are many of these compounds, the first of which was Cp2Rh+. The chemistry of Cp compounds has been extensively studied. A simple example is Cp IrI(C2H4)2. The trivalent compounds [Cp MIIICl(/x-Cl)]2 are very useful starting materials, a recent reaction106 being ... 

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