Hydroxo cationic complexes

The hydrolysis and polymerization of Al3+ under appropriate pH conditions subsequently give rise to the formation of such species as Al(OH)2+, Al2(OH)24+, Al(OH)3, and charged hydroxo cationic complexes, which can effectively remove pollutants. In this study, titanium metal is chosen as anode material mainly for its cheapness and high stability. Some materials with high oxygen evolution have also been reported. When there are some Cl- in the solution, some reactions will occur on the anode by (10.29)-(10.31). 

The photochemistry of Zn+—(CH4) and Zn —(CH3OH) complexes has been studied in detail In that context, the possibility of the formation of a metal-hydroxo insertion complex [HO—Zn—CH3]+ (the isomer of [Zn—(CH30H)]+) has also been discussed . In other series of studies, the mechanism of dimethylzinc zinc monoethyl cation, diethylzinc diethylzinc dimer and dipropylzinc photolysis has been investigated by photoionization techniques. It was the study of Borsella and Larciprete that first observed different gas phase photodissociation mechanisms for Mc2Zn and Et2Zn by using one- and two-color multiphoton ionization combined with TOE MS. 

In 1998, a new type of Pd(II) binuclear complex was reported which was effective for Mannich reactions of an imine derived from glyoxylate and anisidine with silicon enolates [38,39]. In these reactions, use of solvents including a small amount of water was essential. It was shown that water played an important role in this system water not only activated the Pd(II) complex to generate a cation complex, but also cleaved the N-Pd bond of the intermediate to regenerate the chiral catalyst. This reaction reportedly proceeded via an optically active palladium enolate on the basis of NMR and ESIMS analyses. A unique binuclear palladium-sandwiched enolate was obtained in the reaction of the p-hydroxo palladium complex with the silyl enol ether [(Eq. (9)]. 

Tetravalent. The best-studied tetravalent actinide carbon-ato complex is An(C03)5 (An = Th, U, Pu). This anion has been isolated using a variety of cations, including Na+, K+, T1+, [Co(NH3)6] + and C(NH2)3+/NH4+. In solution, the pentacarbonato complex is the end member of the series An(C03) " " (n = 1-5) however, in the mineral tuhokite, Na6BaTh(C03)6-6H20, thorium exists as a hexacarbonato complex. The analysis of the thermodynamic data for these actinide carbonate systems has led to differences of opinion on the actual speciation. The data appear to support both the stepwise addition of C03 and subsequent loss of H2O molecules within the An + cation coordination sphere as well as the formation of mixed hydroxo carbonato complexes, for example Pu(C03)3(0H) . 

If the numbers were accepted at face value, the data indicate that the species involved account for S0-S % of the toxicity, the carbonato complexes do not contribute to toxicity, the anionic hydroxo copper complexes contribute 13-18 to the total toxicity, and the free copper ion and/or the neutral and cationic hydroxo complexes of copper are responsible for 60-70 of the toxicity of copper to aquatic life. 

Bipyridyl and phenanthroline give polymeric 1 1 complexes with eopper(II) chloride 597). The existence of the dimeric ion [(bipy)Cu(OH)2Cu(bipy)] + in solution has been established 177, 566) and it has been isolated as the lilac perchlorate (498). The species (bipy)Cu + has surprisingly large affinity for ligands other than OH (370). The di-/a-hydroxo cation considered above has now been prepared with a variety of counter ions the corresponding phenanthroline salts are also known. There is no evidence of antiferromagnetic interaction between the copper(II) ions even at 80°K (321). When the counter ion is iodide or thiocyanate there is evidence for metal ion-coimter ion interaction. 

The inertness of the dinuclear complexes is greatest in slightly acidic solutions, which therefore have been employed for the reprecipitation reactions. Apparently the chromium systems are much more labile toward bridge breaking than are the cobalt systems. In aqueous solution the meso-[(en)2Cr(OH)2Ci(en)2] cation (I) enters into a rapidly established (t 1 min. at room temperature) equilibrium with the mono-ju-hydroxo complex [(OHXen)2Cr(OH)Cr(en)2-(HaO)] (n) The equilibrium constant K = [II]/[I] is 0.83 in 1 Af NaC104 at 0°. The salts (dithionate, bromide, chloride, and perchlorate) of the di-p-hydroxo cation are less soluble than the respective salts of the mono-/i-hydroxo cation. It is therefore possible to precipitate the pure salts of the di-/i-hydroxo cation from the equilibrium mixture following the procedure given above. 

With the exception of Te(VI), it would appear that all tetra- and hexavalent cations form oxo/hydroxo hydrolyzed complexes in aqueous solution (Table VII). This is particularly apparent when Cl" or Br" are... 

The di- i,-hydroxo bridged complexes, the preparations of which are described in Sections D and H, have several chemical and physical properties in common. The dithionates are only sparingly soluble in water, whereas the bromides are quite soluble. The dinuclear structures of the cations, as well as the A,A configuration of the 1,2-ethanediamine compounds have been established by the close similarity of the Guinier X-ray powder diffraction patterns of [(NH3)4Rh(0H)2Rh(NH3)JBr4-4H20 and [(en)2Rh(OH)2Rh(en)2] (8205)2 to those of the well-characterized cobalt(III) and chromium(III) analogs. 

Isomerisation studies of cobalt(iii) complexes cover a variety of compounds. The rate law for isomerisation of [Co(dien)(OH2)a] + indicates some isomerisation via the hydroxo-cation [Co(OH)dien(OHa)2] +. Rates and activation parameters for direct isomerisation of the tris-aquo-complex were determined. Further kinetic results for isomerisation of cis- and rra 5 -[Co(OH)2 en2]+ in strongly basic solution indicate an intramolecular mechanism. Isomerisation of cw-[CoCl2(diars)2] in methanol is also intramolecular, but isomerisation of cw-[Co(02C CH3)2en2]+ in acetic acid occupies an intermediate position between intra- and inter-molecu-larity, for the essential step is solvent-assisted acetate exchange within ion-pairs. This assignment of mechanism results from consideration of kinetics of acetate exchange as well as of isomerisation. ... 

The cationic methylplatinum(ii) complex with acetone and cod ligands, [PtMe(acetone)(cod)]" , is obtained as a solution from the reaction of AgPp6 with PtClMe(cod) in acetone (Scheme 14). The acetone ligand is substituted easily by a hydroxo anion to give the corresponding neutral hydroxo complex 99. The basic hydroxo ligand of the complex deprotonates acetone to form the methylplatinum(ii) acetonyl complex 100. The cationic complex stabilized by pyridine 101 may be isolated as an analytically pure solid. 

As already mentioned in the hydroxide section above, alkaline solutions of lead contain a complex set of lead hydroxo cations but at low lead concentrations the anion Pb(OH)3 is present. This trihydroxyplumbite is also believed present when precipitated amphoteric lead hydroxide is dissolved in alkali. No evidence for the Pb(OH)5 anion has been found, though solutions of lead hydroxide in strong potassium hydroxide solution are often written as K2Pb(OH)4. 

In an acidic medium, the maximum cation coordination is always achieved in the aquo-hydroxo monomeric complex, and hence the reaction must proceed though nucleophilic substitution. This reaction may take place via one of three simple mechanisms dissociation, association and a concerted mechanism or direct displacement [9]. 

The aquo-complex [ZnlHjOlg] and the tetrahedral [ZnCU] have already been mentioned. Numerous hydroxo-complexes, foi example [ZnfOH) ], [Zn(OH)4] have been described. Additior. of excess ammonia to an aqueous Zn(II) solution produces the tetraamminozinc cation [Zn(N 113)4]-. Hence zinc tends to form 4-coordinate, tetrahedral or (less commonly) 6-coordinate octahedral complexes. 

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