Chromium atom formal oxidation states

The sodium salts Na2[Cr(CO)5] and Na2[Cr2(CO)jo] are yellow solids. Due to the low formal oxidation state of the chromium atom, they are extremely sensitive to air oxidation and must be handled in an inert atmosphere with rigorous exclusion of air. As might be expected from itscoordi-nation number of five, the mononuclear [Cr(CO)s] anion is decomposed by water... 

Cr(CO)sI is isoelectronic with V(CO)6 and like the latter exhibits the expected paramagnetism for a species containing one unpaired electron. Chromium pentacarbonyl iodide appears to be more stable to oxidation but less stable to thermal decomposition than vanadium hexacarbonyl. This higher oxidative stability of Cr(CO)5l as compared with that of V(CO)j may be due to the higher formal oxidation state of the central metal atom of Cr(CO)5l. 

In EC decay, the chemical effects of the X-ray intensity ratio KJK was first observed by Tamaki et al. for various chromium compounds labeled with Cr. A Si(Li) detector was used to measure the X-rays emitted from the nuclide. When the measured data of K, /K, are plotted against the formal oxidation number of diromium, it is seen that the ratio generally increases with the chromium valence number. This is shown in Fig. 2. A notable exception is, however, metallic chromium, where the formal oxidation number does not reflect the electronic state surroimding the chromium atom at all. 

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