Carbon nitrides

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Carbon nitrides are chemical compounds between carbon and nitrogen .

history

The first publication on carbon nitrides with the composition C 3 N 4 comes from Justus Liebig and appeared in 1834. He did not make a heteroatom-free carbon nitride, but a hydrogen-containing polymer that he called melon. Edward C. Franklin later published a theoretical treatise on "ammonocarboxylic acids". These are the condensation reactions of tetraamidomethane via cyanamide and melamine up to C 3 N 4 . In the 1980s, theoretical results that predicted extremely high hardness for C 3 N 4 triggered extensive research.

Carbon nitrides derived from cyan

With nitrogen, carbon forms a series of nitrides with the composition (CN) n (n = 1, 2, x), of which cyan (CN) is only stable at high temperatures. In addition to dicyan NCCN, there are also cyanisocyanate CNCN and diisocyanate CNNC. The polymerization of dicyan (CN) 2 forms paracyan (CN) x . There are also more carbon-rich nitrides C n (CN) 2n + m , which are derived from the hydrocarbons C n H 2n + m through complete substitution of the hydrogen atoms by CN groups. Examples are tetracyanoethylene and dicyanoethine .

If graphite is evaporated in the presence of dicyan, dicyanopolyines are obtained ; H. rod-shaped molecules whose chain ends are occupied by cyano groups. The compounds NC-C 2n- CN with n = 3-8, z. B. C 18 N 2 .

Polymeric carbon nitrides

In addition, there are polymeric carbon nitrides which are obtained by pyrolysis of organic nitrogen compounds such as guanidine or by CVD methods, the composition of which fluctuates and corresponds approximately to C 3 N 4 .

The special interest in the substance class of the compounds also called carbonitrides was aroused in 1984 and 1989, when Sung et al. and Cohen et al., pointed out the high hardness of the crystalline compound C 3 N 4 , which according to the authors' calculations should exceed that of the diamond . Since 1989, theory has continuously developed new structural proposals for the C 3 N 4 . So far, five structure candidates have gained importance, which are accepted to the extent that they all have in common that they are (at best) metastable.

Graphitic carbon nitride (gC 3 N 4 ) is a promising two-dimensional conjugated polymer that can be used as an inexpensive, robust, metal-free and visible-spectrum active photocatalyst for the conversion of solar energy.

In the Si 3 N 4 -analogous carbon nitride forms α-C 3 N 4 and β-C 3 N 4 , the carbon atoms are tetrahedrally surrounded by nitrogen. The corner-linked tetrahedra form a 3D covalent network. In the case of the pseudo-cubic or defective ZnS- analogous C 3 N 4 form, removal of ¼ of the zinc atoms from the zinc blende structure results in a structure of the α-CdIn 2 Se 4 type. The cubic or willemite- II-analogue C 3 N 4 has the highest compression modulus (496  GPa , i.e. significantly higher than diamond) of all C 3 N 4 and the spinel- analogue C 3 N 4 has a structure with octahedrally coordinated carbon.

Carbon nitrides with a fullerene structure

Azafullerenes are fullerenes in which carbon atoms in the fullerene cage have been replaced by nitrogen. The epi-iminofullerenes and ketolactams with an open fullerene cage have proven to be particularly suitable for the synthesis of azafullerenes. Cyanofullerenes are a class of modified fullerenes in which cyano groups are attached to a fullerene skeleton . These have the formula C 60 (CN) 2n , where n takes the values ​​1 to 9.

Other carbon nitrides

Individual evidence

  1. ↑ Elisabeta Horvath-Bordon: Synthesis and properties of carbon nitrides , dissertation, TU Darmstadt, 2004.
  2. ↑ a b Anke Krüger: New Carbon Materials An Introduction . Springer-Verlag, 2007, ISBN 978-3-8351-9098-6 , p. 27 ( limited preview in Google Book search).
  3. ↑ Michaela Krieger-Hauwede, Jen-Hui Chang: Basics and main group elements Volume 1: Basics and main group elements . Walter de Gruyter GmbH & Co KG, 2016, ISBN 978-3-11-049340-5 ( limited preview in the Google book search).
  4. ↑ a b Ralf Steudel: Chemistry of Non-Metals Syntheses - Structures - Binding - Use . Walter de Gruyter, 2013, ISBN 978-3-11-030797-9 , p. 279 ( limited preview in Google Book search).
  5. ↑ Thomas Grösser, Andreas Hirsch: Dicyanpolyine: New rod-shaped molecules from the carbon plasma. In: Angewandte Chemie. 105, 1993, p. 1390, doi : 10.1002 / ange.19931050925 .
  6. ↑ a b Carsten Ludwig Schmidt: Molecules as building blocks for the synthesis of solids: a contribution to the development of new reaction paths in inorganic materials research , dissertation, University of Stuttgart, 2009. doi : 10.18419 / opus-6720
  7. ↑ Yun Zheng, Lihua Lin, B. o. Wang, Xinchen Wang: Polymeric graphitic carbon nitride for sustainable photoredox catalysis. In: Angewandte Chemie. 127, 2015, p. 13060, doi : 10.1002 / anie.201501788 .
  8. ↑ Elena Sheka: Fullerenes Nanochemistry, Nanomagnetism, Nanomedicine, Nanophotonics . CRC Press, 2011, ISBN 978-1-4398-0643-2 , pp. 116 ( limited preview in Google Book search).