Chromium hexacarbonyl properties

Chromium hexacarbonyl is highly toxic by all routes of exposure. The symptoms include headache, dizziness, nausea and vomiting. The LD5o(oral) in mice is 150 mg/kg (Patnaik, P. 1999. A Comprehensive Guide to the Hazardous Properties of Chemical Substances, 2nd ed. NewYork John Wiley Sons). It explodes upon heating at 210°C. 

The transfer of charge from the metal to the ligand caused by back-donation can also be seen from a comparison of the ionization potentials of chromium in different complexes. The ionization potential of complex compounds is higher than that of the uncomplexed coordination center (6.76 eV), e.g. for dibenzenechromium ) 7.07 eV, and for hexacarbonyl-chromium 8.03 eV 43). It may be expected that a decrease in the net positive charge at the coordination center will give rise to an increase in ti-EPD properties. Hence the Fe-C distance will be shorter in [Fe(CO) 4] than in Fe(CO) 5. Likewise iron is more strongly coordinated in ferrocene than in the ferrocinium ion. 

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