Tetrahedrite

Tetrahedrite

  • named after its common outer shape – a tetrahedron
  • because of its relative high copper content it is also a (minor) ore of copper
  • Formula: Cu12[S|(SbS3)4]
  • Space group: I-43m (No. 217)
  • Crystal system: cubic
  • Crystal class: -43m
  • Lattice parameters: a = bc = 10.448 Å, α = β = γ  = 90°

Picture: Carles Millan – http://www.mindat.org/photo-176605.html  | CC BY-SA-3.0


Crystal structure (click on the picture to download the VESTA file):

(K. Momma and F. Izumi, “VESTA 3 for three-dimensional visualization of crystal, volumetric and morphology data,”J. Appl. Crystallogr., 44, 1272-1276 (2011).)

  • SbS3 pyramids (purple)
  • CuS3 trigonal planar coordination (cyan)
  • CuStetrahedra (blue)
  • Copper (blue)
  • Sulfur (yellow)
  • Antimony (purple)

For a 3D interactive version on sketchfab, see here:

https://skfb.ly/6Or6R

Chemistry Hall

While travelling the US for 3 months (that’s the reason why this blog is currently silent 🙂 I received a message from the creators of a blog called Chemistry Hall.

This is a Blog that tries to make people understand how chemistry is important, and how to enjoy learning this incredible science.

This blog provides information in different forms: Research highlights, scientific outreach, educational resources, ways of learning chemistry, fun facts and curiosities, etc. They also love experimentation and share articles about home or hobby chemistry.

Have a look at:

https://chemistryhall.com/

VMOP-beta

The first densest lattice of chemical supertetrahedra?

In one of the last issues of the Angewandte, Wang and coworkers [1] presented an extremely interesting structure, in which metal-organic polyhedra (MOP) are assembled in different ways. These polyhedra consist of polyoxovanadate metal clusters and bridging dicarboxylate linkers. The authors call them VMOP. The overall shape of the MOP can be described as tetrahedron, or to be precise, as truncated tetrahedron see Fig. 1.

Fig. 1: VMOP, in atomistic representation (left) and simplified as a truncated tetrahedron (right).

In fact, the authors obtained two different phases, which differ in the kind of packing: in the VMOP-alpha isomer (a very low-density phase, which is thermodynamically less stable) each truncated tetrahedron makes perfect contact with four neighbors via the (small) four trigonal faces (the truncated faces), thus leading to a dia-like framework (corner-connected tetrahedra).

However, in VMOP-beta the MOPs are packed in a corner-to-face fashion, i.e. each
truncated tetrahedron has contact with eight neighboring tetrahedra (trigonal-to-hexagonal face-to-face-connection), see Fig. 2.

Fig. 2: The eight direct neighbors of a central truncated tetrahedron (in green) in the packing of VMOP-beta.

This packing mode of regular (non-truncated) tetrahedra is known as the densest lattice packing  (i.e. only translations are allowed) of tetrahedra, which was proven in 1969 by Hoylman [2]. The resulting packing density is 18/49 ≈ 36.73 %. Here, each tetrahedron is in contact with 14 others (4 corners + 4 faces + 6 edges). However, in VMOP-beta the 6 edge-edge connections are a bit further apart.

I think, the structure of VMOP-beta is very remarkable and I am not aware of any analogous chemical structure – do you?

PS: I would like to thank Ahmad Rafsanjani Abbasi (ETH Zürich) for bringing this structure to my attention.

References:

[1] Y. Gong, Y. Zhang, C. Qin, C. Sun, X. Wang, Z. Su, Angew. Chem. Int. Ed. 201958, 780.
https://doi.org/10.1002/anie.201811027

[2] D.J. Hoylman, Bull. Amer. Math. Soc. 1970, 76, 135.
https://doi.org/10.1090/S0002-9904-1970-12400-4

 

Afwillite – a calcium nesosilicate

Afwillite

  • Named after the abbreviated discoverer Alpheus Fuller Williams (1874–1953), CEO of De Beers Consolidated Mines at that time
  • Formula: Ca3(SiO3OH)2 · 2 H2O
  • It belongs to the nesosilicates, i.e. there are only isolated SiO4 tetrahedra
  • Space group: Cc (No. 9)
  • Crystal system: monoclinic
  • Crystal class: m
  • Lattice parameters: a = 16.278 Å, b = 5.6321 Å, c = 13.236, α =  γ = 90°, β = 134.898°

Picture: Matteo Chinellato – http://www.mindat.org/photo-356015.html | CC BY-SA 3.0


Crystal structure (click on the pictures to download the VESTA file):

(K. Momma and F. Izumi, “VESTA 3 for three-dimensional visualization of crystal, volumetric and morphology data,” J. Appl. Crystallogr., 44, 1272-1276 (2011).)

  • Oxygen (red)
  • Hydrogen (white)
  • SiO4 tetrahedra (yellow)
  • CaO7 polyhedra (light blue)

For a 3D interactive version, see here:

https://skfb.ly/6J7oy

Stibnite – a black make-up mineral

Stibnite

  • Synonym: Antimonite
  • The mineral has been known since ancient times and was used as a paste with fat as black make-up powder to color eyelids and eyebrows. In Arabic culture, dark eye rims are regarded as the ideal of beauty and at the same time as a magical repellent.
  • Formula: Sb2S3
  • Space group: Pnma (No. 62)
  • Crystal system: orthorhombic
  • Crystal class: mmm
  • Lattice parameters: a = 11.3107 Å, = 3.8363 Å, c = 11.2285 Å, αβ = γ = 90°

Picture: DerHexer, Wikimedia Commons, CC BY-SA 4.0


Crystal structure (click on the picture to download the VESTA file):

(K. Momma and F. Izumi, “VESTA 3 for three-dimensional visualization of crystal, volumetric and morphology data,” J. Appl. Crystallogr., 44, 1272-1276 (2011).)

  • SbS5 tetragonal pyramids (purple)

For a 3D interactive version on sketchfab, see here:

https://skfb.ly/6JoCM


 

Abelsonite – a chemofossil

Abelsonite

  • Discovered only in 1969 (by the way the year of birth of the author of this blog) by Lawrence C. Trudell while he was exploring the Green River Formation (Utah, USA) for an oil shale project
  • Named after Philip H. Abelson (1913–2004), a long-time editor of the journal Science, for his pioneering work in organic geochemistry
  • Abelsonite is formed as a secondary mineral (and is one of the few organic minerals)  on oil shale surfaces by conversion of chlorophyll – therefore, it is called a chemofossil (a fossil that consists only of chemicals remaining from the decomposition of a living organism)
  • Abelsonite is the only known naturally occurring crystalline porphyrin derivative
  • Formula: NiC31H34N4
  • Space group: P-1 (No. 2)
  • Crystal system: triclinic
  • Crystal class: -1
  • Lattice parameters: a = 8.4416 Å, b = 10.8919 Å, c = 7.2749, α = 90.465°, β =113.158°,  γ = 78.080°

Picture: CC BY-SA 3.0 Thomas Witzke – http://tw.strahlen.org/fotoatlas1/abelsonite_foto.html


Crystal structure (click on the picture to download the CIF):

  • Ni: green, N: blue, C: gray, H: white
  • Note: Although a single Ni porphyrin molecule does not possess -1 symmetry, matching ethyl groups at roughly opposite ends of the molecule enable orientational disorder, in which molecules can randomly adopt one of two different orientations while still stacking in the same manner. The aggregate of these two random orientations produces an overall symmetry of P-1.
  • Reference: Crystal structure of abelsonite, the only known crystalline geoporphyrin
    Daniel R. Hummer, Bruce C. Noll, Robert M. Hazen, Robert T. Downs
    American Mineralogist (2017) 102 (5): 1129-1132.
    https://doi.org/10.2138/am-2017-5927

Sartorite

Sartorite

  • Named after Wolfgang Sartorius von Waltershausen (1809 – 1876) Professor of Mineralogy, University of Göttingen, Germany. He was the first who described the mineral.
  • Formula: PbAs2S4
  • Space group: P21/(No. 14)
  • Crystal system: monoclinic
  • Crystal class: 2/m
  • Lattice parameters: a = 19.62 Å, b = 7.89 Å, c = 4.19 Å, α = γ = 90°,  β = 90° (!)

Picture: Rob Lavinsky, iRocks.com – CC BY-SA-3.0


Crystal structure (click on the picture to download the VESTA file):

(K. Momma and F. Izumi, “VESTA 3 for three-dimensional visualization of crystal, volumetric and morphology data,”J. Appl. Crystallogr., 44, 1272-1276 (2011).)

  • PbS9 polyhedra (gray)
  • AsS3 trigonal pyramids (green)
  • Sulfur (yellow)

For a 3D interactive version on sketchfab, see here:

https://skfb.ly/6IYWO