P-1

One down, only 229 to go. Gulp. Eventually, bar a minor filament failure and raft adhesion issues P1 seemed to work ok. So lets go through the same process with P-1. It’s important to remember that this is still a primitive triclinic system (a ≠ b ≠ c , α ≠ β ≠ γ or for the unit cell, the sides a,b and c are not equal, the angles α, β and γ are not equal) and the P-1 space group is related by inversion (hence the ‘-1’) to the P1 space group. But not just a simple inversion, check out; http://pd.chem.ucl.ac.uk/pdnn/symm3/sgtricl.htm for more information.

To the print! Again from the wonderful people at: https://crystalsymmetry.wordpress.com/230-2/

We the get the example:

Chalcanthite CuSO4 • 5(H2O)

http://webmineral.com/data/Chalcanthite.shtml

CIF can be found here:
http://rruff.geo.arizona.edu/AMS/minerals/Chalcanthite

I’m using the one from neutron diffraction data by: ‘G. E. Bacon, D. H. Titterton, Zeitschrift fur Kristallographie, 1975, 141, 330-341′

With the same process of open the CIF in crystal maker and tweak it so we have polyhedra and a thick unit cell line (10 pixels) we get the following structure: (see
https://crystalprint.home.blog/2019/05/06/beginnings-p1/ for a more detailed run through of the process)

Chalcanthite viewed down c. Copper and sulphur polyhedra are blue and yellow respectively. Oxygen and deuterium, red and grey. Extra water molecules and stranded atoms hidden.

Looking pretty good, although I doubt those deuterium (grey, an isotope of hydrogen) positions will print and will cause havoc with my scaffolding. I’ve bumped the relative size of the bonds up to 80 % of the atomic radii of deuterium (remember this is about 3D printing, sometimes sacrifices will have to be made on the chemistry convention – a thicker bond is more representative of the probable electron position anyway..)

The .stl loaded into snapmaker, scaled up by 750 %

Ah. So even with those bonds bumped up to 80 %, and the model scaled up by 750 % we get floating hydrogen atoms. Crystalmaker will only let you increase bonds to 90 % of the atomic radii but even then, they are still not getting picked up by the snapmaker software. I then fiddled with the atomic radii of deuterium (usually 0.04 angstroms) but even having it the same as oxygen (1.2 angstroms), still no bonds!

Right, I’m going to have to slightly off-piste with this one – my number one objective is to print the unit cell of this space group, as faithfully as possible. So I’m going to make some changes to the atomic radii to do this. Firstly I changed the deuterium radii to 0.75 angstroms (it looked silly as 1.2 as well as being very, very wrong). Next in the ‘model>model inspector’ menu I changed entire ball-stick atomic radii to 65 % of actual. Don’t forget, those ball and stick models you see of crystals are not true representative models of the structure, actually there is very little space between the atoms and the spheres (in reality ellipsoids but that is another story), they are shrunk for convenience.

Chalcanthite viewed down c, this time with deuterium (grey) atomic radii set to 0.75 angstroms and then all ball radii scaled to 65 % of actual. Extra water molecules and stranded atoms hidden.

Boom. This looks much better. What about in snapmaker?

Scaled up to 750 %

Looking good, with a raft everywhere and standard snapmaker settings to normal, we’re looking at 30 hours and about 50 m of filament! Looking back at P1 we are printing out at just shy of 100 mm in the largest direction so I think P-1 can be shrunk a tiny bit.. At 550 % scale up we’re getting dimensions of 58.6 x 92.1 x 77.4 mm and a print time of 15 hours. Lets give this a shot, tune in later to find out what happens!

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