Low‐Barrier Hydrogen Bonds in Negative Thermal Expansion Material H3[Co(CN)6]. Issue 27 (25th April 2019)

• Record Type: Journal Article
• Authors: Tolborg, Kasper; Jørgensen, Mads R. V.; Sist, Mattia; Mamakhel, Aref; Overgaard, Jacob; Iversen, Bo B.
• Is Part Of: Chemistry. Volume 25:Issue 27(2019)
• Page Start: 6814
• Page End: 6822
• Publication Date: 2019-04-25
• Subjects: chemical bonding -- electron density -- hydrogen bonds -- neutron diffraction -- X-ray diffraction; Chemistry -- Periodicals; 540
• DOI: 10.1002/chem.201900358
• Languages: English
• ISSNs: 0947-6539

Abstract

Abstract: The covalent nature of the low‐barrier N−H−N hydrogen bonds in the negative thermal expansion material H3 [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. Abstract : The covalent nature of the low‐barrier N−HN hydrogen bonds in the negative thermal expansion material H3 [Co(CN)6 ] has been established based on experimental and theoretical electron density analysis. This shows that strong hydrogen bonding can lead to formation of rigid linkers responsible for negative thermal expansion.