Special Issue "Hypercoordinate Carbon"
Deadline for manuscript submissions: closed (28 February 2023) | Viewed by 8949
Interests: planar tetracoordinate carbon; astrochemistry; quantum chemistry; molecular spectroscopy
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Although tetrahedral tetracoordination is the fundamental paradigm of organic chemistry, the identification of methanium ion, CH5+, in the laboratory through mass spectroscopic measurements challenged the way that one use to think about the coordination tendencies of carbon. While these experiments were carried out in 1950 and officially published in 1952 , it took another 47 years to record the infrared (IR) spectrum of this simple protonated methane . Theoretical studies of two of the lithium carbides, CLi5 and CLi6, further motivated the interest in hypercoordinate carbon compounds. It is noted here that, perhaps, though these compounds are sometimes described as “hypervalent” in the literature, the extra electrons in lithium carbides beyond the usual “octet” are involved with the Li-Li bonding rather than with the Li-C bonding . Therefore, these lithium carbides are hypercoordinate carbon molecules rather than hypervalent carbon molecules. Surprisingly, CLi6 was detected through mass spectroscopic measurements  in 1992, though the theoretical studies were carried out in 1983. Theoretical work on Si2(CH3)7+ and C(CH3)5+, and experimental works on [CCH3]62+, HC[Au(PPh3)]4+, [(C6H5)3PAu5C]+, [(Ph3PAu)6C]2+, C6[CH3]62+, etc., further motivated the interest in hypercoordinate carbon molecules [5-12]. Using anthracene moieties, Akiba and co-workers have shown penta and hexa coordinate organic molecules through X-ray crystallography and theoretical calculations [13-14]. Even in biological systems, such as the iron–molybdenum nitrogenease cofactor existing in diazotrphs, hexacoordinate carbon is predicted to be present .
The idea of making hypercoordinate carbon or silicon, or first-row or second-row elements in general, is not only to examine the coordination behavior of different elements but also to develop new materials. The main objective of this Special Issue is to collect some recent trends in this subject area, as the field is continuously emerging. Therefore, we wholeheartedly welcome contributions from both the experimental and theoretical scientific communities working in this intriguing field.
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 Akiba, K.-y.; Yamashita, M.; Yamamoto, Y.; Nagase, S. Synthesis and Isolation of Stable Hypervalent Carbon Compound (10-C-5) Bearing a 1,8-Dimethoxyanthracene Ligand. J. Am. Chem. Soc. 1999, 121, 10644 – 10645.
 Yamaguchi, T.; Yamamoto, Y.; Kinoshita, D.; Akiba, K.-y.; Zhang, Y.; Reed, C. A.; Hashizume, D.; Iwasaki, F. Synthesis and Structure of a Hexacoordinate Carbon Compound. J. Am. Chem. Soc. 2008, 130, 6894 – 6895.
 Lancaster, K. M.; Roemelt, M.; Ettenhuber, P.; Hu, Y.; Ribbe, M. W.; Neese, F.; Bergmann, U.; S. DeBeer, S. X-ray Emission Spectroscopy Evidences a Central Carbon in the Nitrogenase Iron-Molybdenum Cofactor. Science 2011, 334, 974 – 977.
Dr. Venkatesan S. Thimmakondu
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