Heteropoly Complexes

Mixed heteropolymolybdates and tungstates are present in the 6-heteropoly series. The synthesis of the ammonium salts of the 6-heteropoly anions with nickel as the central atom of the general formula (NH4)4[NiMo6 nWn024H6] has been reported187). All compounds thus obtained are light blue. The preparation of the free acids has also been described187). 

Another class of 12-heteropoly anions involves the replacement of molybdenum by pentavalent vanadium. The molybdovanadophosphoric acids, 

The preparation of the free 10-tungsto-2-vanadophosphoric acid,H5[PW10V2O40], has been described, as well as that of the 8-tungsto-4-vanadophosphoric acid188). 

Niobium, like vanadium, can replace molybdenum in the heteropoly anions. The yellow 10-molybdo-2-niobophosphate anion has been prepared104). The salts (C5HsNH)4H[PMoioNb204o] and [(CH3)4N]4H[PMoioNb2040] have been prepared and characterized. The free acid could not be isolated since it is unstable even in solution104). 

A tungstovanadoselenous acid of composition H6[SeMo,0V204o] xH20 has been prepared by ether extraction and partly characterized189). 

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The existence of a significant interaction between the heteropolyanion and the carbenium ion is supported by the presence of alkyl-heteropoly complexes. Knoth and Harlow (7(57) synthesized O-alkylated compounds such as [(C2H5)30]3PWi2037, where a C2H5 cation is bonded to the polyanion. Fameth et al. (168) and Lee et al. (169) reported the formation of methyl groups and... 

Flynn Jr., C.M. and M.T. Pope. 1971. Tungstovanadate heteropoly complexes. I. Vanadium(V) complexes with the constitution M6019n and V W less than or equal to 1 2. Inorg. Chem. 10 2524-2529. 

The formation of complexes between molybdate ions and H5I06 has been studied148,149. The heteropoly complex first forms upon acidification and thereafter stepwise protonation occurs with final formation of (H6IMo6024)+. 

Recently the synthesis and structure of novel heteropoly complexes has been reported that contain covalently attached groups184). The complexes have the general formula... 

Lin S., Zheng Y., Xu L.-M. and Wang S.-M., Synthesis, characterization and catalytic activity for phenol hydroxylation of rare earth molybdovanadophosphate tetrabasic heteropoly complexes with Keggin structure., Chem. J. Chinese Univ., 21 (2000) pp. 1248 (in Chinese). 

Another characteristic of modem coordination chemistry is the increasing reliance upon physicochemical methods unknown to Werner and his contemporaries. Simultaneously with an introduction of these newer techniques, emphasis shifted from preoccupation with qualitative studies of stmcture and stereochemistry to quantitative studies of thermodynamics, kinetics, and reaction mechanisms. Some areas of current research interest include unusual ligands, oxidation states and coordination numbers, solid-state chemistry, photochemistry, relationship between stmcture and reactivity, variable oxidation state, chelates, heteropoly complexes, organometalhc... 

The molybdo-arsenic acid blue colour is usually excluded from the phosphorus analysis by reduction to arsenious acid prior to the addition of ammonium molybdate to form the heteropoly complex. The complex does not form with arsenious radical. Moreover the P can be precipitated with Al(OH)3 and the precipitate treated with HF, HBr, HCl and H2SO4 to volatilize As, Ge and Si which may be co-precipitated leaving P for analysis. 

The complexes [SiCrWij04o] ,18H20 have been prepared and characterized and the dimetalloheteropolytungstates K AsZ2WjgOg7(OHj25 where Z is usually a first row transition metal ion, have been isolated and their stability and structures discussed. The neutral heteropoly complex [Co2(en)4(H20)2P2Mo5 0 23],8H20 has been prepared and from solution studies and analytical data the complex is best represented as a neutral zwitterionic species. ... 

Osmium(v) and Higher Oxidation States.—Heteropoly complexes containing OsN have been synthesized, as has an octahedral osmium(viii) complex of 3,3 -diamino-4,4 -dihydroxydiphenylsulphone. ... 

It was shown in 1989 by Anson et al." that Fe snbstitnted HPT s can function as catalysts for mnltielectron reduction of nitrite anion to ammonia, a process that requires 6 electrons. While in the presence of many other electrocatalysts that reaction occurs via a sales of one-electron steps and the prodncts inclnde hydroxylamine, in the case of electrocatalysis by a heteropoly tnngstate, no hydroxylamine was observed and the major prodnct of the redaction was ammonia. The first step in the electrocatalytic process observed by Anson is the complexation of nitrite by iron from the heteropoly complex. Next the rednced tnngsten cage serves as a reservoir for the storage of electrons that are snbseqnently transferred to nitrogen in a concerted, intramolecular, multiple electron process. The nniqne catalytic reactivity of the iron snbstitnted HPT in this process was... 

HPLC grade nonpolar solvents, toluene and dichloromethane, were purchased from Aldrich. Toluene was distilled over sodium/benzophenone, and dichloromethane was distilled over calcium hydride. All solvents were stored under nitrogen, over molecular sieves. Water content in dried solvents was typically less than 1 mM. Potassium salts of transition-metal-substituted heteropoly complexes were prepared according to the methods published previously. The IR, UWVIS spectra, and Cyclic Voltammograms agreed... 

The new method reverses the order of the transfer/reduction procedure of the heteropoly complex. Instead of transferring the oxidized TMS HPT into nonpolar solvent and then reducing it in that solvent, we decided to reduce the TMS HPT in aqueous solution first, and transfer the reduced HPT (heteropoly blue) into a nonpolar solvent (toluene). 

For reviews of chemistry of heteropoly complexes see (a) Baker, L.C.W. Click, D.C. Present General... 

Accrete R, Harmalker S, Hammer CP, Pope MT, Baker LCW (1979) Concerning isomerisms and interconversions of 2 18 and 2 17 heteropoly complexes and thdr derivatives. J C S Chem Commun 777-779... 

Qu LY, Shan QJ, Gong J, Lu RQ, Wang DR (1997) Synthesis, properties and characterization of Dawson-type tungstophosphate heteropoly complexes substituted by titanium and peroxoti-tanium. J Chem Soc Dalton Trans 23 4525-4528... 

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