E. Giesbrecht

Lanthanum, cerium and praseodymium trimetaphosphates

Abstract The preparation of compounds with the general formula LnP 3 O 9 ·3H 2 O (where Ln  La, Ce, Pr) is reported. Thermogravimetric analysis of the compounds showed that they decompose to the corresponding phosphates with evolution of P 2 O 5 . Powder diffraction data are presented and the i.r. spectra supported a D 3 h symmetry for the P 3 O 9 3− anion in the above compounds.

Tri- and tetrametaphosphates of lanthanidic elements

Abstract The preparation and properties of some lanthanide trimetaphosphates as well as the corresponding tetrametaphosphates are described. Conductivity measurements and i.r. spectra are presented. The comparison between the neodymium trimetaphosphate and the lanthanide tetrametaphosphate spectra with the spectrum of Nd(BrO3)3. 9H2O suggests that the coordination number of Nd3+ in the tri- and tetrametaphosphate is nine.

Lanthanide chloride complexes with the Schiff Base N-Salicylideneanthranilic acid

Abstract The complexes formed between the lanthanide ions and the Schiff Base N-Salicylideneanthranilic acid ( LH 2 ) in the presence of pyridine have been isolated and characterized. The compounds have been formula [Ln( L H) 2 )(H 2 O)(Cl)] and are solid materials having a reddish-yellow color. They are non-electrolytes in nitrobenzene and the water molecule is not removed by drying at 100°C over P 2 O 5 in vacuo . The interaction between the phenolic oxygen atom and the lanthanide ion does not increase the acidity of the phenolic proton sufficiently that it can be neutralized by pyridine. The shape of the “hyper-sensitive” band in the visible spectrum of the neodymium compound suggests that these compounds are eight-coordinate.

PHOSPHATES AND POLYPHOSPHATES OF THE RARE EARTH ELEMENTS. III. CERIUM(III) TRIPOLYPHOSPHATES

Abstract The reaction between cerium(III) chloride and sodium triphosphate solutions has been discussed. Evidences have been obtained that cerium(III) and triphosphate ions form two insoluble compounds in which the ratios Ce 3+ : P 3 O 10 5− are respectively 5 : 3 and 1 : 1. With excess triphosphate ions a stable solution is obtained. The characteristic absorption spectrum of cerium(III) chloride solutions is changed upon addition of excess sodium triphosphate as a result of the formation of relatively stable complex species. A new maximum between 300–304 mμ is observed. By the method of continuous variations, the complex is formed in the ratio Ce 3+ : P 3 O 10 5− = 1 : 2, in the pH range of 3·0–9·5.

On the reactivity of precursor complexes in the system pentacyanoferrate(II) and pentaammine(dimethylsulfoxide)cobalt(III)

Abstract In the search for evidence of precursor complexes in electron transfer reactions, a binuclear intermediate was detected in the system pentaammine(dimethylsulfoxide)cobalt(III) and aquopentacyanoferrate(II). Cyclic voltammetry measurements and careful analysis of the products indicated that the formation of a sulfuriron bond stabilizes the intermediate with respect to electron transfer reaction. Interpretation of the kinetics data is consistent to the formation of an outer sphere complex (K = 350 M−1) which undergoes internal substitution (k = 20 s−1 to yield the dimethyl sulfoxide bridged intermediate. The binuclear intermediate aquates by breaking the cobalt(III)sulfoxide bond, with a specific rate of 0.106 s−1. ΔH+ = 20 Kcal mol−1 and ΔS≠ = 4 cal mol−1 deg−1, at 25 °C and μ = 0.10 M (lithium perchlorate). Using the less labile amminopentacyanoferrate(II) ion instead of the aquopentacyanoferrate(II) complex, an outer sphere electron transfer reaction with saturation behavior has been observed. For this system, an ion pair association constant of 470 M−1 (ΔH = +2 Kcal mol−1 and ΔS = 20 cal mol−1 deg−1) and an intramolecular transfer rate of 1.22 s− (ΔH≠ = 22 Kcal mol−, ΔS≠ = 17 cal mol−1 deg−1) have been obtained at 25 °C, μ = 0.10 M (lithium perchlorate).

The reaction between dioxane and hydrated lanthanide nitrates

Abstract The reactions between dioxane and hydrated lanthanide nitrates are described. The compounds of formula Ln(NO 3 ) 3 . 2H 2 O.C 4 H 8 O 2 (Ln = La, Ce), Ln(NO 3 ) 3 .2H 2 O.2C 4 H 8 O 2 (Ln = Pr, Nd, Sm) and Ln(NO 3 ) 3 .3H 2 O.2·5C 4 H 8 O 2 (Ln = Y, Gd, Tb, Dy, Ho, Er, Tm, Yb) were prepared and their infra-red spectra studied.

Kinetics of reaction of imidazole, glycine, and L-histidine with the aqua-pentacyanoferrate(II) ion

The properties and reactivity of the pentacyanoferrate(II) complexes of imidazole (imH), glycinate (glyO), and L-histidine (his) are reported. The rates of formation, starting from [Fe(CN)5(OH2)]3–{generated by aquation of [Fe(CN)5(NH3)]3–}, are typically of first order with respect to the concentration of the ligands, with kf= 240, 28.0, and 320 dm3 mol–1 s–1, respectively. The kinetics of dissociation of the complexes, measured in the presence of an excess of dimethyl sulphoxide, show saturation behaviour with respect to this reactant. The limiting rates of dis-sociation are 1.33 × 10–3(imH), 2.67 × 10–3(glyO–), and 5.3 × 10–4 s–1(his) at 25 °C and I= 0.100 mol dm–3(Li[ClO4]). L-Histidine, in zwitterionic form, reacts with [Fe(CN)5(OH2)]3– to yield two isomers in solution. The predominant form contains iron co-ordinated to the hindered N3 nitrogen of imidazole in the L-histidine ligand. This isomer is labile and dissociates rapidly, k= 0.109 s–1 to form the inert and stable N1 isomer. Similar behaviour, but involving the three N-co-ordinating sites of histidine, is observed in alkaline solutions. The strain energy associated with substitution adjacent to the iron centre is estimated as 3,4 kcal mol–1 A correlation of the limiting rates of dissociation with the ligand-field energies in the complexes is presented.

2,2′-sulfinyldiethanol complexes with some first row metal(II) perchlorates

Abstract A number of new complexes containing the potentially tridentate ligand 2,2′-sulfinyldiethanol (sde) is reported. The compounds have the general formula M(sde)n (ClO4)2, in which M = Mn, Co, Ni, Cu, Zn (n = 2) and Fe, Co, Ni, Zn (n = 3). They are characterized and identified by chemical analysis and physical measurements. The compounds have effective magnetic moment values typical of high-spin octahedral complexes. Their i.r. and electronic spectra are discussed. Assignments for the electronic spectra are suggested on the basis of octahedral structure and ligand-field parameters are calculated for nickel and cobalt complexes. The results obtained in this work suggest that sde acts as a tridentate ligand in the 1:2 complexes and as a bidentate one in the 1:3 complexes.

Rates of electron transfer within outer-sphere precursor complexes in the system penta-ammine(dimethyl sulphoxide)cobalt(III) and substituted pentacyanoferrates(II)

The kinetics of outer-sphere electron-transfer reactions between [Co(NH3)5(dmso)]3+(dmso = dimethyl sulphoxide) and a series of [Fe(CN)5L]3– complexes (L = imidazole, ammonia, pyridine, pyrazine, isonicotinamide, or pyrazine-2-carboxamide) have been investigated as a function of the ligand L. The formation constants of the precursor [Co(NH3)5(dmso)]3+∥[Fe(CN)5L]3– complexes are nearly constant in the series (400–550 dm3 mol–1) and practically temperature independent in the range 10–35 °C (ΔH ca. 0, ΔS= 50–55 J K–1 mol–1). The rates of electron transfer in the precursor complexes show a systematic increase from the pyrazinamide to the imidazole complex, with a linear dependence of ln(ket) against ΔE⊖, as predicted theoretically. This increase in rate is paralleled by a decrease in the activation enthalpies from 109 to 92 kJ mol–1, the activation entropies remaining nearly constant at 71–75 J K–1 mol–1.

The kinetics of oxidative substitution in bromopentaamminecobalt(III) ion by chlorine, hypochlorous and hypobromous acids

Abstract A kinetic study of the oxidative substitution reactions of bromopentaamminecobalt(III) with aqueous chlorine, hypochlorous acid and hypobromous acid has been carried out using the stopped-flow technique. For the reaction in excess hypobromous acid the rate law has the form d[Co(NH3)5Br2+]/dt = −k[HOBr][H+][Co(NH3)5Br2+] where k = 3.2±0.2 M−2 sec−1 at 25 °C, μ = 1.0 with ΔH* = 9.4±1.5 kcal/mol and ΔS* = −25±5 e.u. For the hypochlorous acid reaction d[Co(NH3)5Br2+]/dt = −(k+k′[H+])[HOCl][Co(NH3)5Br2+] with k = 4±1 M−1 sec−1 and k′ = 100 ±7 M−2 sec−1. For the k′ step, Δ* = 3.8±1 kcal/ mol and ΔS* = −37±5 e.u. In excess aqueous chlorine the rate law has the form d[Co(NH3)5Br2+]/dt = −k2[Co(NH3)5Br2+][Cl2] where k2 = (A+B[Cl−] + C[Cl−]2+D[Cl−]3)/(1+E[Cl−]+F[Cl−]2). A mechanism is proposed which is consistent with the observed rate law and with the effect of added sulfate ion upon the kinetics of the reaction.