Crystal and Molecular Structure, Spectroscopic Properties, and Electrophilic Reactivity of Sodium Pentacyanonitrosylosmate(II) Dihydrate
Sodium pentacyanonitrosylosmate(II) dihydrate, Na2[Os(CN)5NO]·2H2O, was synthesized by photolyzing a mixture of hexacyanoosmate(II) and nitrite ion, with further purification through ion-exchange and precipitation techniques. The compound is isostructural with the iron and ruthenium analogue species...
| Autores principales: | , |
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| Publicado: |
1994
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| Acceso en línea: | https://bibliotecadigital.exactas.uba.ar/collection/paper/document/paper_00201669_v33_n25_p5890_Baraldo http://hdl.handle.net/20.500.12110/paper_00201669_v33_n25_p5890_Baraldo |
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| Sumario: | Sodium pentacyanonitrosylosmate(II) dihydrate, Na2[Os(CN)5NO]·2H2O, was synthesized by photolyzing a mixture of hexacyanoosmate(II) and nitrite ion, with further purification through ion-exchange and precipitation techniques. The compound is isostructural with the iron and ruthenium analogue species. The crystals are orthorhombic (Pnnm) with a = 6.312 (1) Å, b = 12.090 (2) Å, c = 15.828 (3) Å, and Z = 4. Relevant lengths and angles within the distorted anion octahedra are compared for the three (Fe, Ru, Os) compounds. IR and UV—visible spectral data are also comparatively discussed. The results are indicative of a very strong σ-, as well as back-bonding π-interaction from Os toward nitrosyl and cyanides. The complex is electrophilically reactive toward several bases such as OH-, SH- and N2H4. With OH-, an equilibrium reaction is established, [Os(CN)5NO]2-+ 20H- ⇌ [Os(CN)5NO2]4- + H2O, with K = 42 ± 1 M-2 (I = 1 M, 25.0 °C). From the kinetic and mechanistic analysis, kobs =1.37 × 10-4 M-1 s-1, is determined by the rate of nucleophilic attack of OH- into [Os(CN)5NO]2- in the elementary step. Kinetic and equilibrium results are compared with those obtained for iron and ruthenium pentacyanonitrosyl analogues, as well as for other nitrosyl complexes containing ruthenium and osmium; thus, the different factors influencing nucleophilic rates and affinities are discussed, namely charge, radius and polarizability of the reactants, as well as the energy of the π*(NO) level. The reactions of [Os(CN)5NO]2- with other nucleophiles proceed through initial adduct formation and further decomposition. © 1994, American Chemical Society. All rights reserved. |
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