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Low‐Barrier Hydrogen Bonds in Negative Thermal Expansion Material H 3 [Co(CN) 6 ]
Author(s) -
Tolborg Kasper,
Jørgensen Mads R. V.,
Sist Mattia,
Mamakhel Aref,
Overgaard Jacob,
Iversen Bo B.
Publication year - 2019
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201900358
Subject(s) - covalent bond , hydrogen bond , hydrogen , low barrier hydrogen bond , chemistry , crystallography , neutron diffraction , hydrogen atom , acceptor , molecule , crystal structure , organic chemistry , alkyl , physics , condensed matter physics
Abstract The covalent nature of the low‐barrier N−H−N hydrogen bonds in the negative thermal expansion material H 3 [Co(CN) 6 ] has been established by using a combination of X‐ray and neutron diffraction electron density analysis and theoretical calculations. This finding explains why negative thermal expansion can occur in a material not commonly considered to be built from rigid linkers. The pertinent hydrogen atom is located symmetrically between two nitrogen atoms in a double‐well potential with hydrogen above the barrier for proton transfer, thus forming a low‐barrier hydrogen bond. Hydrogen is covalently bonded to the two nitrogen atoms, which is the first experimentally confirmed covalent hydrogen bond in a network structure. Source function calculations established that the present N−H−N hydrogen bond follows the trends observed for negatively charge‐assisted hydrogen bonds and low‐barrier hydrogen bonds previously established for O−H−O hydrogen bonds. The bonding between the cobalt and cyanide ligands was found to be a typical donor–acceptor bond involving a high‐field ligand and a transition metal in a low‐spin configuration.