I. The Crystal Structures of Certain Intermetallic Compounds: (a) The Nature of the Bonds in the Iron Silicide FeSi and Related Crystals; (b) A Study of the Structure of the Intermediate Compounds MG₂Tl, Mg₂In, and Mg₂Ga. II. Metallic Valence and X-Ray Emission Fine Structure: a Discussion. III. Crystal Structures of Certain Inorganic Compounds: (a) Crystal Structure of Sodium Borohydride; (b) A Redetermination of the Structural Parameters in the Cubic Modification of Arsenious Oxide

Citation

Soldate, Albert Mills (1950) I. The Crystal Structures of Certain Intermetallic Compounds: (a) The Nature of the Bonds in the Iron Silicide FeSi and Related Crystals; (b) A Study of the Structure of the Intermediate Compounds MG₂Tl, Mg₂In, and Mg₂Ga. II. Metallic Valence and X-Ray Emission Fine Structure: a Discussion. III. Crystal Structures of Certain Inorganic Compounds: (a) Crystal Structure of Sodium Borohydride; (b) A Redetermination of the Structural Parameters in the Cubic Modification of Arsenious Oxide. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/82p4-ba49. https://resolver.caltech.edu/CaltechTHESIS:06232025-183816561

Abstract

Part I. Section (a)

The structure of the iron silicide FeSi was determined by means of X-ray single-crystal photography. The previously reported structure was verified. The structure is based upon the space group T⁴ - P2₁3 with a_o = 4.489 ± 0.005 Å. Four iron and four silicon atoms are in the positions (xxx; x + ½. ½ - x, x;) with x_Fe = 0.1370 ± 0.0020 and x_Si = 0.842 ± 0.004.

A detailed discussion of the structure was given in terms of the resonating-valence-bond theory developed by Professor Pauling.

Part I. Section (b)

An investigation of the structures of the intermetallic compounds Mg₂Tl, Mg₂In, and Mg₂Ga was made. The methods of X-ray single-crystal and powder photography were employed. The structures of Mg₂Tl end Mg₂In are based upon the space group D³_3h - C62m with three molecules in a unit cell of dimensions a_o = 8.068 ± 0.005 Å, c_o = 3.457 ± 0.0007 Å; a_o = 8.324 ± 0.005 Å, c_o = 3.457 ± 0.0007 Å, respectively. The three thallium or indium a toms are in the positions

1: (a) 000,

2: (c) ⅓ ⅔ ½; ⅔ ⅓ ½.

The six magnesium atoms are in the positions

3: (f) x₁00; 0x₁o; x₁x₁0

3: (g) x₂0½; 0x₂½; x₂x₂½.

In the case of Mg₂Tl x₁ = 0.3746 ± 0.0028 and x₂ = 0.2866 ± 0.0038. It was not possible to fix the parameters x₁ and x₂ accurately in the instance of Mg₂In, but it is highly probable that they do not differ greatly from the corresponding values of Mg₂Tl in terms of the resonating-valence-bond theory^(1),(2) was given and it was found that the valences of the thallium atoms are larger than that exhibited in the elementary substance.

The structure of Mg₂Ga is apparently similar to that of Mg₂Tl and Mg₂In. The positions of the atoms, however, necessitate a doubling of the unit cell dimension along the c axis. It was not possible to determine the exact position of the atoms.

Part II.

A discussion is given of the relationship between metallic valence and the fine structure of the X-ray emission bands of metals, alloys, and intermetallic compounds. The study of fine structure seems to offer a chance to gain valuable information concerning metallic valences; there is, hov1ever, a great need for more experimental information.

Part III. Section (a)

The structure of sodium borohydride was investigated by means of X-ray powder photography and found to be based on a face-centered cubic lattice. The unit cell of dimensions a_o = 6.151 ± 0.009 kX contains four sodium and four boron atoms arranged in the following manner:

4 Na at ooo, o½½, ½o½, ½½o

4 B at ½½½, ½oo, o½o, oo½

It is probable that the structure consists of tetrahedral BH^-₄ ions and Na⁺ ions. The dimensions of the ions would permit oscillation or rotation of the BH^-₄ tetrahedra.

Part III. Section (b)

The structural parameters of the cubic modification of arsenious oxide have been redetermined by means of X-ray powder and single crystal photography and found to agree closely with those reported by Almin and Westgren⁽⁵⁾.

The structure is based upon the packing of As₄0₆ molecules which have the same dimensions as those found for the molecules of the gas^(2),(12).

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