C. Robert Dennis

Synthesis of cesium octacyanomolybdate(V)- and cesium octacyanotungstate(V) dihydrate: a more successful method

SummaryExisting methods for the preparation of Cs3[Mov(CN)8]· 2H2O and Cs3[Wv(CN)8]·2H2O are not always successful. Nitrite ions in an acidic medium prove to be a very effective oxidizing agent for this synthesis. It was however found that the product yield was hydrogen ion-dependent and that an excess, considerably more than the stoichiometric amount, was necessary for optimal yields.

The oxidation of octacyanotungstate(IV) by nitrite ions in acidic medium

Abstract The kinetics of the oxidation of octacyanotungstate(IV) by nitrite ions has been studied in aqueous perchloric acid medium between 0.01 and 0.5 M HClO 4 . An acid dissociation constant for HW(CN) 8 3− , K a = 0.26 ± 0.2 M at 25°C and I = 1.0 M, is obtained from the kinetic data.

A kinetic study of the oxidation of hydroxylamine by octacyanotungstate(V)

Abstract The kinetics of the oxidation of hydroxylamine by octacyanotungstate(V) ions has been studied over a wide pH range. The reaction is first-order in both oxidant and reductant. The kinetically determined dissociation constants, Ka1 = 2.5 ± 0.5 × 10−6 M and Ka2 = 3.2 ± 8.0 × 10−14 M, are in agreement with values obtained from the literature.

Proton-transfer reactions of copper(II)- and nickel(II) tetrapeptide complexes with bulky α-carbon substituents

Protonation of copper(II)- and nickel(II) tetrapeptide complexes with bulky α-carbon substituents has been studied. The pKa-values for the second and terminal metal–N(peptide) bond formation have been determined spectrophotometrically. More than one deprotonated peptide nitrogen exists in a complex but the individual protonation steps for the different CuII–N(tetrapeptide) positions could not be accounted for by the variation of the hydrogen ion concentration in the same experiment, as the protonation of the different metal–N(tetrapeptide) positions takes place at different wavelengths. For the NiII-tetra-alanine complex, the proton transfer to the terminal and second deprotonated peptide nitrogens have been detected by varying the hydrogen ion at the same wavelength. The proton transfer to the terminal metal–N(tetrapeptide) of CuII- and NiII-tetrapeptide complexes show first order kinetics with respect to the hydrogen ion and the peptide complex concentration and proceed via an outside protonation pathway. The relatively high pKa values for the terminal deprotonated peptide nitrogen indicate the instability of this metal–N(peptide) bond due to strain in the chelate ring because of atom overcrowding of the bulky α-carbon substituents.

The oxidation of octacyanomolybdate(IV) and octacyanotungstate(IV) by nitrous acid

Abstract The kinetics of the oxidation of octacyanomolybdate(IV) by nitrous acid has been studied in aqueous perchloric acid medium. An equilibrium concentration of the nitrosonium ion, NO+, has been proposed as the active oxidizing species. An acid dissociation constant for H[Mo(CN)8]3−, Ka = 0.47 ± 0.05 M at 25°C and I = 1.0 M has been obtained from the kinetic data.