Caren Sullivan’s favorite structure is:

Bismuth

Bismuth

Source: Theodore Gray

Why?

A thin oxide layer results in a beautiful iridescent surface coating the bismuth crystals. Bismuth has a relatively low melting point, so you can melt it down and make these crystals at home in steel cookware! They're relatively easy to make, but also contain incredibly complex and mysterious crystal structures! One of Nature's most beautiful creations!—Caren Sullivan

Allison Fleshman’s favorite structure is:

Poly(ethylene oxide)3:LiCF3SO3

PEOLiTf_Zardalidis

Source: Zardalidis, et al. Macromolecules, 2013, 46,
2705-2714

Why?

The phase diagram of the 3:1 compound of  polyethylene oxide with lithium Trifluoromethanesulfonate is beautiful! It's also a common crystal in the polymer electrolyte world. I consider it an 'old friend'.
Allison Fleshman

Kranthi Kumar Namila’s favorite structure is:

N-acetyl L-cysteine

overlay

Source: CrystEngComm, 2013, 15, 6498

Why?

A novel polymorph of N-acetyl-L-cysteine (NAC) is discovered three decades after the first report on the X-ray crystal structure of this bioactive compound. The crystal structure of the new orthorhombic polymorph (form II in the P212121 space group) is characterized by X-ray diffraction and compared to the triclinic structure of form I (NALCYS02 and NALCYS10 in the P1 space group). Both polymorphs contain a C(7) chain of COOH…OLC–CH3 hydrogen bonds, except that the COOH group is rotated by 180u in form II
to make an auxiliary C–H…O interaction with the methyl group in a R2 2(8) ring motif. The known form I contains weak S–H…OLC–OH and N–H…S hydrogen bonds whereas the new form II has only N–H…S interactions.—Kranthi Kumar Namila

Sudalai Kumar S’s favorite structure is:

Water-Ice

Water-Ice

Source: University of Hyderabad

Why?

Perfect tetrahedral arrangements of water molecules through hydrogen bonding in the crystal lattice makes the the ice less denser than the liquid water. This is one of the peculiar behaviour of water in the solid state. The photo shown here is taken from University of Hyderabad during the hail storm in 4th March 2014. Photo Courtesy: HCU Students.—Sudalai Kumar S

Hilmar Koerner’s favorite structure is:

Nematic phase under external fields

Nematic phase under external fields

Source: taken myself with CCD image at CHESS

Why?

Liquid Crystal phases are not only beautiful under the polarizing optical microscope with a colorful display of textures. 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

Alexander Bayden’s favorite structure is:

HIV-1 Protease Complexed with KNI-1689

3A2O

Source: Created from PDB described in Hidaka, Koushi, et al. “Small-sized human immunodeficiency virus type-1 protease inhibitors containing allophenylnorstatine to explore the S2′ pocket.” Journal of medicinal chemistry 52.23 (2009): 7604-7617.

Why?

This is the one of the highest resolution structures of HIV-1 protease. The reason I like it is because this protein is challenging in many ways. For decades we have been trying, but were unable to create a cure for HIV. HIV-1 protease is especially tricky. Its crystals of are notoriously hard to prepare because this protein eats up the cells that produce it in significant amounts. In addition to that, there are non-standard protonation states in the active site of HIV-1 protease. They change depending on the ligand bound and the pH of the environment.—Alexander Bayden

Keith Werling’s favorite structure is:

2-methyl-4-nitroaniline

Why?

The first paper that I was first author on involved using ab initio quantum mechanics to calculate the piezo coefficient of 2-methyl-4-nitroaniline. This was one of the first papers to show that hydrogen-bonds can exhibit a significant piezoelectric response. I'm now using the methods that I have since developed from these initial calculations to find organic crystals that show piezo responses that can compete with the many inorganic ceramics that are the leading piezoelectric materials.  Hopefully the diversity of organic materials will broaden the uses of piezo materials.  An example would be the use of flexible film piezoelectrics in the use of pacemakers!  Wish I could upload a graphic from my paper, but I don't have a laptop with me  =(—Keith Werling

cory reidl’s favorite structure is:

DapE

Why?

I think DapE, a homodimer diZn metaloprotease that can modulate its catalytic activity by substituting one of its metals with Co, Mn or Mg, is an awesome crystal structure because it has been found it has been found to be a target for drug targeting and it can act as a programmable protease.—cory reidl

David Blake’s favorite structure is:

First pXRD pattern from Mars

2-D_Pattern

Source: NASA/JPL-CalTech/Ames

Why?

The Mars Science Laboratory rover Curiosity has been operating on Mars since Aug. 6, 2012. Curiosity carried with it the first spaceflight-qualified X-ray Diffractometer, a breadbbox-sized XRD called CheMin. CheMin returned the first XRD pattern from another planet in 2012, nearly coincident with the centennial of the discovery of X-ray diffraction by von Laue in 1912. The transmission-geometry 2D pattern, in the same geometry as those obtained by von Laue, provided the first quantitative mineralogy of the Mars surface (D.L. Bish et al., Science 341, 1238932 (2013)). A second CheMin analysis identified an ancient habitable environment on Mars (D.T. Vaniman et al., Science 343, 1243480 (2014)—David Blake