Antonio Cervilla

Model compounds for the active sites of oxo-transfer molybdoenzymes. Synthesis, structural characterization, and electrochemical properties of [NH4]2[MoO2{O2CC(S)Ph2}2]

[NH4]2[MoO2{O2CC(S)Ph2}2]middot;2H2O has been prepared and its crystal structure solved, providing the first example of a co-ordinatively saturated molybdenum complex which reacts readily and reversibly with organophosphines at room temperature in water or methanol; its variable-temperature 13C{1H} NMR spectra and electrochemical properties are presented.

Simultaneous determination of stoichiometry, degree of condensation and stability constant: A generalization of the molar-ratio method

A generalization of the molar-ratio method is proposed, which allows study of relatively weak complexes. The method is based on treatment of the data from a molar-ratio saturation curve. From the mathematical expression derived, the stoichiometry, degree of condensation and stability constant are easily evaluated. Graphical representations of the results can be used advantageously.

Mo(VI) oxalate complexes

Mo(VI) and oxalic acid give rise to three different stable complex species in aqueous solution, namely {MoO2(OH)2(C2O4)2}4−(log Kt=15.52±0.03) , {Mo2O5(OH)2(C2O4)2}4−(log Kt=16.5±0.2) , and {Mo2O5(OH)2(C2O4)2}3−(log Kt=14.6±0.1) , Stoichiometry and condensation degree are a function of the pH. The formation equilibria are studied spectrophotometrically and by saline cryoscopy. The three species mentioned above have been isolated as {Co(en)3}3+ salts and characterized by X-ray diffraction powder and IR spectra. The results show that oxalic acid behaves in the same way as the tartaric acid and as the malic acid when there is an excess in the latter.

Improving epoxide production using Ti-UVM-7 porous nanosized catalysts

Nanosized Ti-UVM-7 materials with a hierarchical system of pores at two different length scales have been prepared through a one-pot procedure by using a simple template agent; the catalytic activity and selectivity of the resulting materials in bulky olefin epoxidation by organic peroxides are the highest reported to date.

Compounds of tungsten(VI) with citric acid: A spectrophotometric, polarimetric and hydrogen-1, carbon-13 N.M.R. study of the formation and interconversion equilibria in aqueous solution

SummaryTungsten(VI)-citrate complexes, which occur in aqueous solution, were studied by polarimetric and absorbance measurements. The pH of the medium is the principal variable controlling complex formation and interconversion equilibria. At high pH (>6), the stable complexes are monomers with 1∶2 and 1∶1 stoichiometry, depending on the tungsten(VI)-citrate ratio, while at lower pH two different dinuclear complexes are formed. The intervals of existence of these species with the pH, the number of equivalents of acid necessary for their formation, as well as the conditional stability constant, have also been calculated.The structure of these compounds have been investigated by1H and13C-n.m.r. spectroscopy. The n.m.r. results indicate the existence in all these species of strong, covalent metal-toligand oxygen bondingvia the carboxylic oxygen atom and the adjacent hydroxylic oxygen.

Compounds of WVI with 1(+)-sorbitol: Study of formation and interconversion equilibria

SummaryThe polarimetric study of the WVI-sorbitol system shows the formation of three stable complexes. The species stable at higher pH is monomeric ([WO(OH)(C6H12O6)2]−), while the other two are dinuclear complexes of different stoichiometries ([W2O3(OH)4(C6H10O6)]−2 and [W3O3(OH)(C6H11O6)2]−). The interconversion equilibria have been established and the formation constants determined. The behaviour of sorbitol is like that displayed by other polyhydroxylic ligands having one or two carboxylic groups. The substitution of a carboxylic group for an alcoholic one seems only to result in lower stability constants for the complexes formed.

On the atomic environment and the mode of action of the catalytic centre in an intercalated oxo–molybdenum complex [MoO2{O2CC(S)Ph2}2]2– for oxygen-transfer reactions

The title anion accommodated as a pillar in the interlamellar space of a Zn(II)AlIII double hydroxide(hydrotalcite-like) host is shown by X-ray absorption spectroscopy, supplemented by other studies, to possess three terminal MoO groups, in contrast to the two that exist in the dispersed, catalytically active anion.

Molybdenum(VI)-dioxo complexes with sterically bulky thiocarboxylate ligands. Reactions with aliphatic thiols and electrochemical properties

Abstract Under acid conditions, the reaction of (Bu n 4 N)2[Mo VI O 2 (O 2 CC(S)Ph 2 ) 2 ] with aliphatic thiols yields the monomeric [Mo V O(O 2 CC(S)Ph 2 ) 2 ] − as unique complex product. The experimental pseudo-first order rate constant with respect to the Mo(VI) complex was found to be K =6.1 × 10 −5 s −1 . At neutral pH, however, an unstable Mo(IV) species was formed which was also electrochemically detected in a reversible Mo(V,IV) couple. [Mo V O(O 2 CC(S)Ph 2 ) 2 ] − appears to be obtained by the reaction of [Mo IV O(O 2 CC(S)Ph 2 ) 2 ] 2− with unreacted [Mo VI O 2 (O 2 CC(S)Ph 2 ) 2 ] 2− . Steric features on the ligand (gemdiphenyl groups) explain that the latter reaction does not lead to the expected formation of μ-oxo Mo(V) dimers. [Mo V O(O 2 CC(S)Ph 2 ) 2 ]− undergoes a one-electron reversible reduction on the cyclic voltammogram time scale, being also oxidized by nitrate ions to the starting Mo(VI) complex. The relation of these results to enzymatic systems is briefly discussed.

Lactate complexes of molybdenum (VI)

SummarySpectrophotometric and cryoscopic studies of the molybdenum(VI)-lactic acid (C3O3H6) system show the existence of three different oxoanion complexes in aqueous solution which have been isolated as [Co(en)3]3+ salts. These are one molybdodilactate {[MoO2(C3O3H42]2−} and two dinuclear 1/1 species: [Mo2O5(C3O3H4)2(H2O)2]2− and [Mo2O3(OH)3-(C3O3H4)2]−. The pH of the medium is the main variable, controlling the formation equilibria which are similar to those previously described for other α-hydroxy-acid ligands.

Electrochemical reduction of the nitrite to ammonium ions in presence of [MoO2(O2CC(S)C6H5)2]2−

Ammonia is formed during potentiostatic reduction of sodium nitrite solutions on the nafion-complex-coated electrode. When (NH4)2[MoO2(O2CC(S)(C6H5)2)2] is present in NaNO2 solutions a polarographic wave is associated to electrocatalytic reduction of nitrite ion. The wave height varies linearly on the concentration of nitrite ion, allowing a procedure for analysing this ion. This electrochemical behaviour distinguishes the nitrite from the nitrate ions. The Mo(VI), Mo(V), and Mo(IV) are involved in catalytic redox processes determining formation of NH4+ from nitrite ions.