Paramagnetism, feeble

Chromium(II) acetate monohydrate, discovered by Peligot in 1844, is the best known chromium(II) compound because it can be precipitated readily from aqueous Cr11 solutions by sodium acetate, is stable in air for short periods, and is used as a reducing agent and a source of other chromium(II) compounds (Table 9). Nonetheless, in its deep red colour, feeble paramagnetism and acetate-bridged, binuclear structure (24) (determined in 1953 and refined in 1971),154155 which are still not completely understood, it differs sharply from other chromium(II) salts (Section 35.3.5.1). 

All at the complexes are diamagnetic. A feeble paramagnetism in a few complexes may be due to paramagnetic impurities. ° Additional ligand containing nitrogen donor. 

Nitric oxide dimerizes in the solid state (Fig. 9-2). Dimers persist in the vapor at the boiling point where the structure is similar but the N—N distance is longer (2.237 A) and the ONN angle is 99.6°. The binding energy of the dimer, —16 kJ mol-1, is consistent with the long N—N bond. The dimer has no unpaired spins but feeble intrinsic temperature-independent paramagnetism. Unstable forms can be isolated in matrices. 

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