A team of researchers from the University of Chicago and Emory University has found evidence of a hybrid hydrogen bond / covalent bond. In her paper published in the journal Science, describes the group of experiments they have performed with bifluoride ions that distinguish the line between hydrogen bonds and covalent bonds. Mischa Bonn and Johannes Hunger with the Max Planck Institute for Polymer Research have published a Perspectives piece in the same journal issue outlining the work of the team on this new effort.
One of the basic concepts of chemistry is that the bonds between hydrogen atoms are electric and weak, and thus are not true chemical bonds. Covalent compounds, on the other hand, are true chemical bonds and are therefore strong – and they are what typically hold molecules together. Covalent bonds gain their power by dividing electrons between the atoms involved. In this new effort, the researchers have found what appears to be an exception to this rule – a hybrid type of binding.
The researchers worked with groups of bifluoride ions – each made by placing a hydrogen atom between two fluorine atoms in an aqueous solution. According to the rules of chemistry, the triplets should be held together by the hydrogen atom that forms a covalent bond with one of the fluorine atoms and a hydrogen bond with the other. But when the researchers tested the triplets with infrared light to vibrate them, they found something surprising. Instead of the expected decrease between energy levels as the atoms climbed the energy ladder, they found an increase – a sign that the hydrogen atom seemed to be split between the two fluorine atoms. Computer calculations showed that the behavior they observed depended on the distance between the atoms. It was only when the fluorine atoms were closest together that the hybrid bond was observed. As the fluorine atoms were further removed from the hydrogen atom, normal bonding took over.
The researchers called the hybrid a hydrogen-mediated chemical bond, noting that it could not be described as either a hydrogen bond or a covalent bond – it was indeed a hybrid of the two. They also note that their findings have implications for understanding basic chemistry and the true nature of chemical bonds.
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Bogdan Dereka et al. Crossover of hydrogen to chemical bonding, Science (2021). DOI: 10.1126 / science.abe1951
Mischa Bonn et al. Between a hydrogen and a covalent bond, Science (2021). DOI: 10.1126 / science.abf3543
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Quote: Experiments with Bifluoride Ions Show Evidence of Hybrid Bonds (2021, January 8) Retrieved January 8, 2021 from https://phys.org/news/2021-01-bifluoride-ions-evidence-hybrid-bonds.html
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