C(2)N: A Class of Covalent Frameworks with Unique Properties

C(2)N is a unique member of the C(n)N(m) family (carbon nitrides), i.e., having a covalent structure that is ideally composed of carbon and nitrogen with only 33 mol% of nitrogen. C(2)N, with a stable composition, can easily be prepared using a number of precursors. Moreover, it is currently gaining extensive interest owing to its high polarity and good thermal and chemical stability, complementing carbon as well as classical carbon nitride (C(3)N(4)) in various applications, such as catalysis, environmental science, energy storage, and biotechnology. In this review, a comprehensive overview on C(2)N is provided; starting with its preparation methods, followed by a fundamental understanding of structure–property relationships, and finally introducing its application in gas sorption and separation technologies, as supercapacitor and battery electrodes, and in catalytic and biological processes. The review with an outlook on current research questions and future possibilities and extensions based on these material concepts is ended.