quaternary compound
{{Short description|Chemical compound made of four elements}}
File:Quaternary ammonium cation.svg. The Rs may be the same or different groups. (The Rs may also be connected, making a cyclic ion.)]]
In chemistry, a quaternary compound is a compound consisting of exactly four chemical elements.
In another use of the term in organic chemistry, a quaternary compound is or has a cation consisting of a central positively charged atom with four substituents, especially organic (alkyl and aryl) groups, discounting hydrogen atoms.{{GoldBookRef|title=Onium compounds|file=O04291}}
The best-known quaternary compounds are quaternary ammonium salts, having a nitrogen atom at the center.{{GoldBookRef |file= Q05003 |title= Quaternary ammonium compounds}} For example, in the following reaction, the nitrogen atom is said to be quaternized as it has gone from 3 to 4 substituents:
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Other examples include substituted phosphonium salts ({{chem2|R4P+}}), substituted arsonium salts ({{chem2|R4As+}}) like arsenobetaine, as well as some arsenic-containing superconductors.{{cite journal |last1= Ren |first1= Z. A. |last2= Yang |first2= J. |last3= Lu |first3= W. |last4= Yi |first4= W. |last5= Shen |first5= X. L. |last6= Li |first6= Z. C. |last7= Che |first7= G. C. |last8= Dong |first8= X. L. |last9= Sun |first9= L. L. |last10= Zhou |doi= 10.1209/0295-5075/82/57002 |first10= F. |last11= Zhao |first11= Z. X. |title= Superconductivity in the iron-based F-doped layered quaternary compound Nd[O1 − x Fx]FeAs |journal= EPL |volume= 82 |issue= 5 |pages= 57002 |year= 2008 |bibcode= 2008EL.....8257002R |arxiv= 0803.4234|s2cid= 119268175 }} Substituted stibonium ({{chem2|R4Sb+}}){{cite journal |last1= Widler |first1= H. -J. |last2= Schwarz |first2= W. |last3= Hausen |first3= H. -D. |last4= Weidlein |first4= J. |title= Tetramethyl-Arsonium- und -Stibonium-Methylchlorometallate des Galliums und Indiums |doi= 10.1002/zaac.19774350124 |journal= Zeitschrift für anorganische und allgemeine Chemie |volume= 435 |pages= 179–190 |year= 1977 }} and bismuthonium salts ({{chem2|R4Bi+}}) have also been described.{{cite book|title=Chemistry of arsenic, antimony, and bismuth|author=Nicholas C. Norman|publisher=Springer Netherlands|year=1997|page=316|isbn=0-7514-0389-X|url=https://books.google.com/books?id=vVhpurkfeN4C&q=tetramethyl+bismuthonium&pg=PA316}}