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Abstract:

The new complex, K3[Os(CN)5NH3]·2H2O, a convenient precursor for the pentacyano-L-osmate(II) series, was prepared and characterized by chemical analysis, cyclic voltammetry, and IR and UV-vis spectroscopies. By controlled aquation in weakly acidic medium, the [Os(CN)5H2O]3- ion was generated. Weak absorptions in the UV region for L = H2O, NH3, and CN- were found at 287, 272, and 240 nm, respectively, and were assigned to d-d transitions, in terms of a model for tetragonally distorted ions also valid for the members of the iron and ruthenium series. The kinetics of the formation and dissociation reactions of the [Os(CN)5L]n- ions, L = pyridine (py), pyrazine (pz), N-methylpyrazinium (mpz+), etc., were studied. At 25.0 °C, the formation rate constants for the neutral ligands pz and isonicotinamide were ca. 0.13 M-1 s-1 and slightly increased for L = mpz+ and decreased for isonicotinate. The enthalpies of activation were ca. 22.0 kcal mol-1, independently of the entering L, and the activation entropies were all positive, ca. 11-13 cal K-1 mol-1. The dissociation reactions showed a saturation rate behavior of kobs (s-1) as a function of the concentration of the scavenger ligand. The specific dissociation rate constant at 25.0 °C was 1.06 × 10-7 s-1 for L = NH3 and around 10-9 s-1 for py, pz, and mpz+ (extrapolated to 25.0 °C from values measured in the range 60-95 °C). These small values are associated with high activation enthalpies (range 30-35 kcal mol-1) and positive activation entropies (range 10-20 cal K-1 mol-1). The evidence for both the formation and dissociation processes shows that dissociative mechanisms are operative, as for the iron and ruthenium analogues.

Registro:

Documento: Artículo
Título:Kinetics and mechanism of ligand interchange in pentacyano-L-osmate(II) complexes (L = H2O, NH3, N-heterocyclic ligands
Autor:Slep, L.D.; Alborés, P.; Baraldo, L.M.; Olabe, J.A.
Filiación:Departamento de Química Inorgánica, Analítica y Química Física, INQUIMAE, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Pabellón 2, Ciudad Universitaria, Buenos Aires C1428EHA, Argentina
Palabras clave:ammonia; heterocyclic compound; iron derivative; isonicotinamide; isonicotinic acid; ligand; nitrile; osmium derivative; pyrazine derivative; pyridine derivative; ruthenium derivative; water; acidity; article; chemical analysis; chemical reaction kinetics; cyclic potentiometry; dissociation; enthalpy; entropy; infrared spectroscopy; synthesis; ultraviolet spectroscopy
Año:2002
Volumen:41
Número:1
Página de inicio:114
Página de fin:120
DOI: http://dx.doi.org/10.1021/ic010923a
Título revista:Inorganic Chemistry
Título revista abreviado:Inorg. Chem.
ISSN:00201669
CODEN:INOCA
CAS:ammonia, 14798-03-9, 51847-23-5, 7664-41-7; isonicotinamide, 1453-82-3; isonicotinic acid, 16887-79-9, 55-22-1; water, 7732-18-5
Registro:https://bibliotecadigital.exactas.uba.ar/collection/paper/document/paper_00201669_v41_n1_p114_Slep

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Citas:

---------- APA ----------
Slep, L.D., Alborés, P., Baraldo, L.M. & Olabe, J.A. (2002) . Kinetics and mechanism of ligand interchange in pentacyano-L-osmate(II) complexes (L = H2O, NH3, N-heterocyclic ligands. Inorganic Chemistry, 41(1), 114-120.
http://dx.doi.org/10.1021/ic010923a
---------- CHICAGO ----------
Slep, L.D., Alborés, P., Baraldo, L.M., Olabe, J.A. "Kinetics and mechanism of ligand interchange in pentacyano-L-osmate(II) complexes (L = H2O, NH3, N-heterocyclic ligands" . Inorganic Chemistry 41, no. 1 (2002) : 114-120.
http://dx.doi.org/10.1021/ic010923a
---------- MLA ----------
Slep, L.D., Alborés, P., Baraldo, L.M., Olabe, J.A. "Kinetics and mechanism of ligand interchange in pentacyano-L-osmate(II) complexes (L = H2O, NH3, N-heterocyclic ligands" . Inorganic Chemistry, vol. 41, no. 1, 2002, pp. 114-120.
http://dx.doi.org/10.1021/ic010923a
---------- VANCOUVER ----------
Slep, L.D., Alborés, P., Baraldo, L.M., Olabe, J.A. Kinetics and mechanism of ligand interchange in pentacyano-L-osmate(II) complexes (L = H2O, NH3, N-heterocyclic ligands. Inorg. Chem. 2002;41(1):114-120.
http://dx.doi.org/10.1021/ic010923a