Quaternary compound
In chemistry, a quaternary compound is a cation consisting of a central positively charged nitrogen atom with four substituents, especially organic (alkyl and aryl) groups, discounting hydrogen atoms.
The best known quaternary compounds are quaternary ammonium salts, having a nitrogen atom at the centre. For example, in the following reaction, the nitrogen atom is said to be quaternized as it has gone from 3 to 4 substituents:
Other examples include substituted phosphonium salts (R4P+), substituted arsonium salts (R4As+) like arsenobetaine, as well as some arsenic containing superconductors. Substituted stibonium (R4Sb+) and bismuthonium salts (R4Bi+) have also been described.
...
Wikipedia