Lead hydroxide complexes

Reaction of [Ir( -Cp )Cl2(/A-Cl)2]2 and pyrazole in the presence of potassium hydroxide leads to complex 105 characterized by the dynamic hydrogen bond between three pyrazole nuclei (86AGE1114). 3,5-Dimethylpyrazole in identical conditicHis produces 106 where two pyrazole nuclei share a proton and one is unprotonated. Addition of tetrafluoroboric acid to 106 yields 107, where the second proton is bonded to the nonchelated ligand. Addition of the third proton causes formation of [Ir( -Cp )(Hpz )3](BF4)2. 

Cathodic protection is a useful supplement to other forms of water treatment, as a general corrosion inhibiting device in HW boilers, or where specific design configurations can lead to inadequately protected localized metal in steam boilers. Where BW makeup demands are minimal and boiler output is fairly constant, cathodic protection devices can also provide some measure of protection against hardness scales. Calcium carbonate salt is formed as a floc-culant or soft sludge rather than a hard scale, due to the peptizing effects of a zinc hydroxide complex formed from zinc ions in alkaline BW. 

The observation that the pH of salt solutions, especially of those containing polyvalent metal ions, decreases on heating has lead to a different, yet very elegant, technique to generate well-defined metal (hydrous) oxides. Obviously, the increased acidity of such solutions must be due to the release of protons from the hydrated cations, which in turn change to hydroxide complexes. This process was termed by the senior author as forced hydrolysis (7,9-11). At appropriate temperatures and... 

In light of the accepted mechanism for cytochrome P-450 (97-100), a superoxo-Cu(II) intermediate is further reduced, leading to dioxygen activation. Accordingly, a monomeric peroxo or hydroperoxo copper(II) complex serves as a synthetic model for these intermediates of copper-containing monooxygenases. However, no well-characterized complexes of these types are available to date. Formation of a monomeric hydroperoxo or acylperoxo complex was reported to occur when a trans-/u-l,2-peroxo complex, [(Cu(TPA))2(02)]z+, was treated with H+ or RC(O)+, but no details of the structures and properties of the complexes were provided (101). A related complex, a monomeric acylperoxo cop-per(II) complex, was synthesized (102). Low-temperature reaction of a dimeric copper(II) hydroxide complex, [Cu(HB(3,5-iPr2pz)3)]2(OH)2, with 2 equivalents of m-CPBA (3-chloroperoxybenzoic acid) yielded a monomeric acylperoxo complex whose structure was characterized by... 

Addition of ammonium carbonate to a solution containing an actinide(III), (IV),(V) or (VI) ion gives the following results. Only actinide(VI) ions form soluble carbonato complex ions. Actinide(III) and (IV) ions precipitate as their hydroxides or basic carbonates, and actinide(V) ion precipitates as a double carbonate. Therefore, in dilute ammonium carbonate medium, U(VI) ion can be separated primarily from Np(V), Pu(IV), Am(III) and Cm(III) ions. Further addition of ammonium carbonate leads to complex ion formation and the dissolution of actinide(IV) precipitates. However, most of the actinide(III) and (V) ions remain as precipitates under this condition. Crystalline precipitates of actinide(IV) and (VI) carbonato complex anions are formed by addition of hexamminecobalt(III), hexaureachromium(III) or hexa-mminechromium(III) salt to the ammonium carbonate solution containing actinide(IV) and (VI) ions. 

Lead compounds were once widely used also for paints. They were in great demand because they covered surfaces well and were available in a number of vivid colors. Among these were lead chromate (yellow), lead molybdate (reddish-orange), lead(II) oxide (canary yellow), red lead oxide (Pb304 red), and white lead, a complex lead carbonate/lead hydroxide mixture. As with other lead compounds, however, the potential health hazards of the element have greatly reduced the availability of lead-based paints. 

Lead (Pb, at. mass 207.19) occurs in its compounds in the II and IV oxidation states. Compounds of lead(IV) have acidic properties. Lead hydroxide, Pb(OH)2, is amphoteric, precipitating within the pH range 7-13. Lead(II) forms strong tartrate, acetate, thiosulphate, and EDTA complexes. The halide complexes are relatively weak. 

Lead enters surface water from atmospheric fallout, run-off, or wastewater. Little lead is transferred from natural minerals or leached from soil. Pb ", the stable ionic species of lead, forms complexes of low solubility with major anions in the natural environment such as the hydroxide, carbonate, sulfide, and sulfate ions, which limit solubility. Organolead complexes are formed with humic materials, which maintain lead in a bound form even at low pH. Lead is effectively removed from the water column to the sediment by adsorption to organic matter and clay minerals, precipitation as insoluble salt (the carbonate, sulfate, or sulfide) and reaction with hydrous iron, aluminum, and manganese oxides. Lead does not appear to bioconcentrate significantly in fish but does in some shellfish such as mussels. When released to the atmosphere, lead will generally occur as particulate matter and will be subject to gravitational settling. Transformation to oxides and carbonates may also occur. 

The released metal ions are covered by a hydration shell, the size of which depends on the valency of the ion and the size of the nucleus. The hydrate complexes [M(H20) ] of multi-valent ions can deprotonate (i.e. they act as acids), which affects the chemical equilibrium of the reaction (3.21). As a result, the apparent solubility is a function of the pH-value. Deprotonation leads to a transformation of the hydrate complexes into hydroxide complexes [M(OH) ] ". The neutral hydroxide complexes are hardly soluble. The total amount of dissolved material and its composition can be calculated from the acid-base-equilibria of the complex ions and the pH. In general, the lower the main group of the metal is, the higher the oxide solubility. 

Condensation of formaldehyde with D-[ C]glucose catalysed by 3—5 M calcium hydroxide at 100 °C gave D-fructose, D-mannose, D-arabinose, dihydroxyacetone, glyceraldehyde, and glycolaldehyde. Isotope studies confirmed that the rate of retroaldol cleavage of the aldose was considerably less than the rate of carbohydrate synthesis. The pH changes and the complex formation of the same reaction with either calcium hydroxide or lead hydroxide have been investigated. ... 

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