SCIENCE & TECHNOLOGY
YOUR FAVORITE CRYSTAL STRUCTURES GRAND PRIZE WINNER is among the hundreds of X-ray crystal
structures our readers picked as their favorites
JEFFREY BACON
C60@[10]CYCLOPARAPHENYLENE
There are many structures of various species encapsulated within fullerenes, but this one turns the tables. A buckyball is captured inside a cycloparaphenylene with nearideal π-π interactions all the way around.—Jeffrey Bacon
ZEOLITE BETA
MOUND SCIENCE & ENERGY MUSEUM
β-RHOMBOHEDRAL BORON The beautiful, strikingly unique structure of β-rhombohedral boron has successfully withstood numerous challenges of its correctness and has for a half-century experienced nearly constant investigations of its structurally implied material characteristics. Arguably the most important of the several known phases of elemental boron, this form has been found to be experimentally stable from absolute zero to its melting point. Detailed consideration of the fivefoldness of its numerous discrete and merged 12-atom regular icosahedral motifs and their extended 84-atom truncated icosahedral arrays has forced a significant modification of chemical bonding theory in attempts to explain the low-density, high-strength, high-melting, semiconducting, and other notable properties of this low-atomic-number element. As one affected colleague has remarked: “You never fully recover from a bite of the boron bug.” This structure illustrates some of the allure.—Don Bruce Sullenger (shown in this 1965 photo)
MORE ONLINE
GEOFFREY PRICE
LAST MONTH we celebrated the International Year of Crystallography by picking a few of our favorite X-ray crystal structures—and challenged our readers to do the same. More than 300 of you did just that. Among the most-loved structures? Water ice, DNA, and C60. But there were many dark horse candidates too. Overall, your answers surprised us, delighted us, and even made us laugh. Here we reveal our grand prize winner—Geoffrey Price, a chemical engineering professor at the University of Tulsa, who will take home a 3-D printer for his entry on the structure of an intergrowth of two zeolite polymorphs—as well as the runners-up. Visit http://cenm.ag/favecrystals to weigh in with your favorite.
My favorite crystal is zeolite beta (BEA), an intergrowth of two polymorphs, which I am holding in the picture. You can think of beta somewhat like taking these two models, shaving them into layers, and shuffling them like a deck of cards. I originally saw the structure of beta in 1985 in the Mobil labs in Princeton, N.J., where I had Grand taken a consulting job workPrize ing in Roland von Ballmoos’s Winner group. The structure fascinated me because one of the polymorphs contains a spiral pore. Could it be grown in enantiomeric forms? Could it be used to separate enantiomers of organic compounds? In my exit interview, I was told specifically that the structure of beta was one the top secrets of the company. Nothing could be said about it. Scroll forward four years to 1989 at Exxon’s Clinton, N.J., labs. I was again a consultant and was in the office of John Newsam. Sitting on his desk was a model of a zeolite. I picked it up to examine it, and because of the spiral pore, I recognized it as zeolite beta. Thirty years later, I am still fascinated enough to build a digital model of the structure and have the two polymorphs printed.—Geoffrey Price
See all of our readers’ favorite X-ray crystal structures at http://cenm.ag/favecrystals. CEN.ACS.ORG
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POLONIUM
WIKIMEDIA COMMONS
It can’t get any simpler than this. Polonium is the only crystal with a simple cubic lattice and one-atom basis. How on Earth could this be a thing? —Maciej Malinowski α-HEMOLYSIN α-Hemolysin is one of the very few protein structures that’s not only breathtakingly pretty and intricate but is also the epicenter of a true technological breakthrough: It is the linchpin of nextgeneration DNA sequencing technology. By utilizing the solventfilled channel as a nanopore, researchers are threading DNA strands through it and sequencing individual nucleotide bases by looking at minute changes in electrical current across the pore. α-Hemolysin is as good an example as I know of nature’s unsurpassed ability to create both beauty and utility in one fell swoop.—Ashutosh Jogalekar WIKIMEDIA COMMONS
COURTESY OF JES SHERMAN
PENTACENE Pentacene is one of the lab rats of organic electronics. It has been widely studied in the solid state, grown into thin films, and derivatized for improved solubility or different packing or more interesting electronic properties. The structure that is tattooed on my back is not surprising, crystallographically. Pentacene is not my favorite because of the molecule itself but because of all the research it has enabled—including my own Ph.D. investigations. Crystal structures provide great insight into the physical properties of organic semiconductors. We can use the information to calculate electronic structure or predict crystal habit. Beyond single-crystal structure determination, diffraction data are useful in exploring interesting physical properties such as negative thermal expansion and determining how well ordered thin films are. In the right hands, a crystal structure is a very useful tool.—Jes Sherman
FERROCENE
Haiku To Ferrocene
Twenty-one atoms A whole new world for science Iron in the heart. —Stephanie Hurst
HILMAR KOERNER
Liquid-crystal phases are not only beautiful under the polarizing optical microscope. They also are beautiful in reciprocal space, especially when seen in real time under external fields, such as electric or magnetic fields. It looks majestic when the molecules switch orientation and you see the X-ray pattern change from equatorial to meridional on demand.—Hilmar Koerner
MARS X-RAY DIFFRACTION PATTERN
NASA/JPL-CALTECH/AMES
LIQUID-CRYSTAL PHASES
The Mars Science Laboratory rover Curiosity has been operating on Mars since 2012. Curiosity carried with it the first spaceflight-qualified X-ray diffractometer, called CheMin. CheMin returned the first X-ray diffraction pattern from another planet in 2012, nearly coincident with the centennial of the discovery of X-ray diffraction by Max von Laue in 1912. The transmission geometry 2-D pattern, in the same geometry as that obtained by von Laue, provided the first quantitative mineralogy of the Mars surface (Science 2013, DOI: 10.1126/science.1238932).—David Blake
BIS(OCTAETHYLPORPHYRIN)ZIRCONIUM(IV) I am currently a high school student intent on pursuing a career in organometallics. One of the main reasons why I love this field is the limitless amount of possibilities. From complex clusters to novel catalysts, there are seemingly no bounds on the structures of the product. In this regard, bis(octaethylporphyrin)zirconium(IV) is exemplary of why I find this subject so intriguing.—David Wang
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