[OsmiumTetroxide]

Cyanocobalamin  (vitamin b12) has a -CN group attached to Co...why isnt it poisonous? its vitamin b12 which we consume daily.

what i know (maybe wrong)
--> -CN group is not hindered so it can participate in chemical reactions somewhat easily
--> if it can... CN^- ions are produced which is lethal
--> as there are electron donating groups near to Co,.. CN can easily be eliminated (not substituted)

My Info :- Studying in class 12 (CBSE India)
The question maybe useful for engineering entrance exams

[Corribus]

Cyogenic compounds are toxic because they liberate free cyanide ions easily. There are a number of organic compounds with C≡N functional groups that are not toxic because they don't liberate cyanide in sufficient quantities to be harmful. This is one such molecule.

(The reason cyanide is toxic is because it binds irreversibly to heme, and thus interferes with cellular respiration. Essentially the C≡N in cyanocobalamin is bound irreversibly to the metal center of a porphyrin already, so there's no reason for it to be toxic.)