Valence State Of Cr Research Articles

Chromium ions within zeolites. Part 1.—Infrared, electron spin resonance and temperature-programmed reduction studies of the valence states of chromium ions

It has been found that CrIII ions introduced into NH4Y zeolites and their stabilized form SY are not reduced in vacuo but readily reduced by hydrogen to CrII in the temperature range 570–870 K. The absorption of NO on CrIII and CrII ions takes place with the formation of dinitrosyl complexes which exhibit, in both cases, practically identical i.r. and e.s.r. spectra. Thus the adsorption of NO cannot be used for the determination of Cr valence state in zeolites. Oxidation of CrIII ions to CrV and CrVI occurs with retainment of zeolite crystallinity. Non-skeletal oxygen ligands bound in complexes of CrV and CrVI are easily released from oxidized zeolite. These complexes are not stable, CrVI being more readily reduced than CrV. The results were obtained by means of i.r. and e.s.r. spectra of adsorbed NO, e.s.r. spectra of CrV ions, t.p.r. of zeolites by hydrogen and mass-spectrometric detection of oxygen released from zeolites.

Low-temperature magnetic susceptibilities of NbSe 2 containing the first-row transition metals

The magnetic susceptibilities of the systems M x NbSe 2 ( M = V, Cr, Mn, Fe, Co, Ni) were measured from liquid helium temperature to room temperature. All the metal atoms M showed a localized magnetic moment, except Co, which showed a temperature independent magnetic susceptibility. From the experimental magnetic moments the valence states of Cr, Mn and Fe could be concluded, but not for V and Ni.