The Application of the Three Dimensional Patterson Method and the Crystal Structures of Proustite, Ag₃AsS₃, and Pyrargyrite, Ag₃SbS₃

Author: Harker, David

Year: 1936

Degree: Dissertation (Ph.D.)

Advisor: Pauling, Linus

Committee Member: Unknown, Unknown

Option: Chemistry

DOI: 10.7907/7x7x-cv79

Abstract

It is shown that the three dimensional Patterson method can be so simplified by the use of the symmetry properties of the crystal under consideration that its use in determining the positions of atoms in crystals is practicable. This method is then used to determine the positions of the heavy atoms in proustite, Ag3AsS3. The positions of the sulfur atoms are found by the use of the covalent atomic radii and assumptions concerning bond directions. The structure so derived is found to be compatible with the observed data. Proustite is found to contain pyramidal AsS3 groups and silver atoms forming two bonds to sulfur in almost opposed directions. Pyrargyrite, Ag3SbS3, is found to have almost the same structure as proustite. The analytical statement of the structures is as follows:--

The space group C63v - R3c, is common to both proustite and pyrargyrite. The special positions of C63v are (in hexagonal axes)

2a) 0,0,z; 0,0,½+z

6b) x,y,z; y,x-y,z; y-x,x,z;

y,x,½+z; x,x-y,½+z; y-x,y,½+z;

and positions derived from these by the operations of the rhombohedral lattice. The parameter values are:--

Proustite

ao = 10.74 Å, co = 8.64 Å

2As in 2a) ZAs = 0.000

6Ag in 6B) xAg = 0.246

yAg = 0.298

zAg = 0.235

6S in 6b) xS = 0.220

yS = 0.095

zS = 0.385

Pyrargyrite

ao = 11.04 Å, co = 8.71 Å

2Sb in 2a) ZSb = 0.000

6Ag in 6B) xAg = 0.250

yAg = 0.305

zAg = 0.210

xS = 0.220

yS = 0.105

zS = 0.355

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