Magnetic moment of chromium

Table 75 Electronic Spectra and Magnetic Moments of Chromium(III) Biguanide Complexes...

Magnetic moment of chromium complexes were found in the range of 4.0-4.50 B.M. These values of magnetic moment support the predicted geometry of... 

Tris(bipyridine)ehromium(II) perchlorate is stable for long periods in dry air but slowly oxidizes when wet. It has a room-temperature magnetic moment of 3.0 B.M., typical of a low-spin chromium(II) compound.18... 

Chromium(II) chelates of 3-(N-2-furfuralideneimino)propionic acid (HFP), o-(JV-ar-furfurali-dene)benzoic acid (HFB), and o-(N-ar-furfuralideneimino)ethanesulfonic add (HFE)284-286 have been found to have magnetic moments of approximately 4.8 BM at room temperature. A band near 14500 cm-1 (CHC13 solution) has been assigned to the % 5T transition and formation constants have been measured. However, there is no indication of difficulties arising from the air sensitivity of chromium(II) solutions. 

The magnetic moment of the 4s-valence electron of a chromium and a copper atom is cancelled out by the magnetic moment of a neighbouring atom s valence electron. All atoms in the table, except for copper, have unpaired electrons in d-orbits due to which you would expect a magnetic moment. They exhibit this behaviour when they are placed in an external magnetic field. As soon as this external magnetic field is switched off, the magnetism in the metals disappears. 

Besides the oxide Cr02 and the chromates(IV) (see Section 3.3), there exists a number of Cr alkoxides [Cr(OR)4] derived from tertiary alcohols. These are volatile blue liquids or low-melting sohds with effective magnetic moments of ca. 2.8/tb The crystal structure of [Cr OCH(r-Bu)2 4] has been determined and confirms the tetrahedral coordination geometry of chromium. The short Cr distances (177.3 pm) indicate significant ligand metal 7T-donation. 

There has been a report of bridged dinitrogen complexes of iron(III) and chromium(lll) complexes, formed by reaction of the metallo(IlI)porphyrinate triftate with [Re(N2)(PMe2Ph)4Cl] to make the Fe-N-N-Re or Cr-N-N-Re bridged complexes. The Fe complex has a magnetic moment of about 4.4 /u-b at room temperature, consistent with a S = 312,512 admixed spin state for the iron(lll), and a pyrrole-H shift of -3.23 ppm, consistent with the expected weak-fteld nature of the N2 ligand. The stracture shows a linear Fe-N-N-Re unit (Fe-Nl-N2 = 170°, Nl-N2-Re = 177°) with Fe-N bond length of 1.93 similar to that of the TPPFe -azide complex (1.953 A). 

The magnetic moments of the compounds which contain both chromium(iii) and iron(iii) compounds are slightly lower than expected for low-spin and high-spin complexes of these metals (Table 3) which suggests a weak interaction between the two paramagnetic ions (Fe and Cr ). 

Chromium(iv) compounds are perhaps slightly more numerous and stable than those of chromium(v), but still relatively rare. Some mixed oxides, M2Cr04, M CrOs and M4CrOe are known but only the blue-black M2Cr04 compounds containing Ba and Sr are well characterized. These air-stable compounds contain discrete Cr04" ions with magnetic moments of 2.8 B.M. they are made, e.g., by the reaction... 

In the chromia-alumina catalyst system we are primarily concerned with the phenomena of paramagnetism and antiferromagnetism, both of which are due to the magnetic moments of the chromium ions. The magnetic susceptibility (y) of a paramagnetic material such as chromia-alumina is related to the absolute temperature (T) according to the Curie-Weiss law... 

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