Molecules of the Year

First confirmed inorganic double helix

Chemists led by Tom Nilges of the Technical University of Munich reported the first completely inorganic double-helix compound, SnIP, which is a semiconducting material featuring a twisted tin iodide (SnI⁺) chain intertwined with a twisted phosphide (P^–) chain. The chains are held together by weak interactions between tin and lone pairs of electrons on phosphorus, and each double helix is coordinated to neighboring ones by interactions that are stronger than hydrogen bonding in DNA (Adv. Mater. 2016, DOI: 10.1002/adma.201603135).

Presenting a ferrocene Ferris wheel

By directly fusing ferrocene molecules together, Michael S. Inkpen, Nicholas J. Long, and Tim Albrecht of Imperial College London and their colleagues prepared new iron-based macrocycles that resemble a Ferris wheel. The redox-active nanorings, with versions containing five to nine ferrocene units, offer possibilities for trapping ions or molecules to sense or control them, as well as for electronic and magnetic applications (Nat. Chem. 2016, DOI: 10.1038/nchem.2553).

Cesium hosts 16 fluorine atoms

Klaus-Richard Pörschke and coworkers of the Max Planck Institute for Kohlenforschung reported a new molecule in which a central cesium atom is coordinated by an unprecedented 16 fluorine atoms from five anion units. Matching the large, singly charged Cs⁺ cation with the weakly coordinating [H₂NB₂(C₆F₅)₆]^– anion allowed the researchers to go beyond 12 bonds in a complex for the first time without using hydrogen as one of the coordinating ligands. It also was the first time scientists achieved 16 bonds to one metal, which is thought to be the maximum possible (J. Am. Chem. Soc. 2016, DOI: 10.1021/jacs.6b02590).

Chromium complex wins bonding triple crown

In 1978, David N. Clark and Richard R. Schrock of Massachusetts Institute of Technology reported a tungsten alkyl-alkylidene-alkylidyne complex notable for being the first compound containing single, double, and triple metal-ligand carbon bonds in the same molecule. Fast-forward to this year, and Evan P. Beaumier and Aaron L. Odom of Michigan State University and their colleagues reported the first nitrogen analog, a chromium amido-imido-nitrido complex (Chem. Sci. 2016, DOI: 10.1039/c5sc04608d).

Pnictogens make chain-link progress

Alexander Hinz of Oxford University and Axel Schulz and Alexander Villinger of the University of Rostock thought it would be nice to make a heterocyclic ring containing four different pnictogens (group 15 elements, N to Bi). They ended up unable to close the linear precursor to make the ring, but the acyclic compound still included an unprecedented Sb–N–As=P chain. The researchers say that in principle it should be possible to include bismuth, which would be a periodic table first to incorporate all elements from one group in a molecular complex (Chem. Eur. J. 2016, DOI: 10.1002/chem.201601916).

New world champion base and polar molecule crowned

By preparing the o-diethynylbenzene dianion in a gas-phase experiment, Berwyck Poad of Queensland University of Technology and coworkers set the record for theworld’s strongest chemical base, as measured by the molecule’s proton affinity. The dianion is strong enough to deprotonate benzene in the gas phase, the researchers say, and its proton affinity record is unlikely to be broken (Chem. Sci. 2016, DOI: 10.1039/c6sc01726f). Meanwhile, a research team led by Klaus Müllen of the Max Planck Institute for Polymer Research made a hexasubstituted benzene in which electron-withdrawing cyano groups and electron-donating amino groups combine to pull and push the molecule’s electron density in the same direction. This compound is remarkable for being the most polar neutral molecule now known to exist (Angew. Chem. Int. Ed. 2016, DOI: 10.1002/anie.201508249).