Ice V and XIII

Ice V and XIII

  • can be formed by slowly cooling liquid water at ~ 5 kbar from 20 °C to – 20 °C
  • density: 1.23 g/cm3

Structural features

  • Ice V is a proton-disordered phase
  • the analogous proton-ordered phase is Ice XIII
  • all water molecules are hydrogen-bonded to four others, two as donor and two as acceptor, at distances of 2.76 to 2.87 Å
  • the coordination tetrahedra are largely distorted with angles ranging from 84 to 128°.
  • Ice V contains 4,- 5-, 6-, and 7-membered rings
  • Space group: A2/a (No. 15)
  • Crystal system: monoclinic
  • Lattice parameters:
    • a = 9.22(2) Å, b = 7.54(1) Å, c = 10.35(2) Å
    • α = γ = 90°, β =109.2(2)°
    • 28 molecules per unit cell

 Here, you can download the CIF.

Literature:

[1] B. Kamb, A. Prakash, C. Knobler, Structure of Ice V, Acta Cryst. 1967, 22, 706-715. DOI: 10.1107/S0365110X67001409

Atomistic structure figures were created with

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

Vermiculite – Mineral of the Year 2019 in Austria

Vermiculite

  • The mineral was first described in 1824 by Thomas H. Webb. Due to the property of the mineral to expand into worm-like formations when heated to 200 to 300 °C in the direction of the crystallographic c-axis, Webb named it after the Latin word “vermiculor” for “worm breeder”.
  • On the occasion of the 195th anniversary of its discovery and due to its great importance as an industrial mineral, vermiculite was voted “Mineral of the Year” in Austria in 2019.
  • Formula: Mg0,7(Mg,Fe,Al)6(Si,Al)8O20(OH)4 · 8 H2O
  • Space group: C2/c (No. 15)
  • Crystal system: monoclinic
  • Crystal class: 2/m
  • Lattice parameters: a = 5.349 Å, b = 9.255 Å, c = 28.89, α = γ = 90°, β = 97.12°

Picture: CC BY-SA 3.0 Leon Hupperichs


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).)

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

https://skfb.ly/6OKvO

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