13859-51-3Relevant articles and documents
Preparation of carbon supported cobalt by electrostatic adsorption of [Co(NH3)6]Cl3
D'Souza,Regalbuto,Miller
, p. 157 - 169 (2008)
Our previous paper [L. D'Souza, L. Jiao, J.R. Regalbuto, J.T. Miller, A.J. Kropf, J. Catal. 248 (2007) 165] presented the synthesis of cobalt catalysts on carbon (Timrex) and silica supports by strong electrostatic adsorption (SEA), using a cobalt hexaamine chloride ([Co(NH3)6]Cl3, CoHA) precursor. The CoHA undergoes reductive deammination in an uncontrolled manner in the presence of NaOH and adsorbs as Co3O4 on carbon with broad size distribution. The present paper extends these studies toward the end of synthesizing well-dispersed Co oxide particles in a narrow size range on carbon supports using NH4OH. Cobalt uptake versus pH was determined in NH4OH and NaOH basified solutions over a number of carbons with varying point of zero charge (PZC). The resulting materials were characterized by ICP, powder XRD, XAS, TPR and STEM. CoHA in the presence of NH4OH adsorbs as well dispersed as CoO, Co3O4 and Co(OH)2-4 depending upon the pH of the adsorption solution. These phases were undetectable by powder XRD and STEM Z-contrast imaging, but could be identified by XAS. Additionally, non-adsorbed CoHA complexes underwent transformation to [Co(NH3)5Cl]Cl2 at pH > 11 in solution. After calcinations of 250 °C, particle sizes of Co3O4 range from 20-50 A from NH4OH and 50-200 A from NaOH. Maximum metal uptake was approximately 3.3 and 2.7 μmol/m2 in presence of NaOH and NH4OH, respectively. The SEA method of preparation was compared with incipient wetness impregnation (IWI) of Co(NO3)2s6H2O; this method yields Co3O4 particles after 250 °C calcinations which are almost as small or in one case, smaller than the calcined SEA samples. Higher metal loadings can be achieved by the SEA method by successive adsorption steps with a little variation in particle size and distribution. However, the main advantage of SEA is in forming mono- or submonolayer of different Co oxide phases on carbon surface.
NMR spectroscopy of the solid-state isomerization of nitrito- and nitro-pentamminecobalt(III) chloride
Ooms, Kristopher J.,Wasylishen, Roderick E.
, p. 300 - 308 (2006)
Cobalt-59 and nitrogen-15 NMR spectra of the nitritopentamminecobalt(III) chloride, [(NH3)5Co-ONO]Cl2, and nitropentamminecobalt(III) chloride, [(NH3)5Co-NO 2]Cl2, isomers in the solid state have been obtained at several applied magnetic field strengths. The 59CQ NMR line shapes indicate that both the cobalt nuclear quadrupolar coupling constant (CQ) and the span of the chemical shift tensor (Ω) decrease when the complex isomerizes from [(NH3)5Co-ONO] 2+ to [(NH3)5Co-NO2]2+; CQ decreases from 23 to 10.3 MHz and Ω changes from 1650 to 260 ppm. The 15N NMR line shapes also show a significant change in the nitrogen magnetic shielding tensor upon isomerization, with Ω decreasing from 710 to 547 ppm; also, an indirect spin-spin coupling, 1J( 59Co,15N) = 63 Hz, is observed in the 15N NMR spectra of the nitro isomer. The NMR parameters are rationalized based on differences in the molecular structure of the two isomers. NMR spectra have also been recorded as the isomerization progresses with time and demonstrate the practicality of the technique for the study of solid-state isomerizations.
Lemay, H. Eugene Jr.,Babich, Michael W.
, p. 147 - 154 (1981)
Influence of the metal centers on the pKa of the pyrrole hydrogen of imidazole complexes of (NH3)5M3+, M(III) = Co(III), Rh(III), Ir(III), Ru(III)
Fazlul Hoq,Shepherd, Rex E.
, p. 1851 - 1858 (2008/10/08)
The pKa's at 298 K, μ = 0.10 (NaCl), and the temperature dependence (273-343 K) for the deprotonation of the pyrrole NH of several imidazoles coordinated to (NH3)5M3+ moieties (M = CoIII, RhIII, IrIII, RuIII) are reported. A greater importance of dn configuration over ion size is found. Data summarized for various systems are as follows (ligand, M (pK298, ΔHa° in kcal/mol, ΔSa° in eu)): imidazole = imH, CoIII (9.99, 14.0 ± 0.5, 1.3 ± 1.6), RhIII (9.97, 13.6 ± 0.3, 0.1 ± 1.3), IrIII (10.05, 13.4 ± 0.3, 1.2 ± 1.0), RuIII (8.9, 10.0 ± 0.8, 3.7 ± 1.2); 2-methylimidazole = 2-MeimH, CoIII (10.67, 17.8 ± 0.7, 11.2 ± 2.4); 2,4(5)-dimethylimidazole = 2,5-Me2imH, CoIII (11.04, 13.4 ± 0.5, 5.3 ± 1.6), RuIII (10.20, 13.2 ± 0.6, -2.1 ± 1.6). 1H NMR spectra of low-spin d6 complexes of imidazoles and ring-methylated imidazoles are discussed for CoIII, RhIII, IrIII, and RuIII. C-2 and remote ring, C-5, substituents are shifted downfield relative to the free imidazole ligand in the order H+ > CoIII > RhIII > IrIII. The C-4 position is influenced competitively by σ-withdrawal ring substituents and TIP effects for CoIII. Assignments of the remote isomer for (NH3)5M(2,5-Me2imH)3+ (M = CoIII, RuIII) are made from the 1H NMR spectra of the CoIII and RuII complexes. The RuIII complexes of 2,5-Me2imH and the imidazolate form (2,5-Me2im-) both exhibit LMCT spectra. The imidazolato form has three bands at 655, 377, and 272 nm, proposed for II1 → IId, II2 → IId, and n → IId transitions, where II1, II2, and n are the highest HOMO's of the imidazolato ring.
