I. A Study of the Allotropes of Selenium. II. Evidence for Existence of a Selenium-Iodine Compound. III. An Attempt to Reproduce the Allison Magneto-Optic Effect. IV. The Crystal Structure of Potassium Chlorosmate and Potassium Bromosmate

Citation

McCullough, James Douglas (1936) I. A Study of the Allotropes of Selenium. II. Evidence for Existence of a Selenium-Iodine Compound. III. An Attempt to Reproduce the Allison Magneto-Optic Effect. IV. The Crystal Structure of Potassium Chlorosmate and Potassium Bromosmate. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/z4wx-2g84. https://resolver.caltech.edu/CaltechTHESIS:11072024-231343892

Abstract

I.

A new vacuum-vaporization method for determination of transition temperatures, due to Dr. A. O. Beckman, has been tested and proven to be all right by means of the mercuric iodide transition at 127° .

This method shows an apparent transition between a red micro-crystalline form of selenium and the hexagonal form at a temperature of 74-75°C.

The relative stability of the three crystalline forms of selenium at 25° has been definitely established as:

(1.) hexagonal selenium (most stable).

(2.) α - monoclinic selenium.

(3.) β - monoclinic selenium (least stable).

II.

Evidence quoted in the literature which supposedly disproves compound formation between iodine and selenium in no case prohibits the possibility of a highly dissociated compound.

Absorption spectra were photographed which give strong evidence favoring a selenium-iodine compound in solution.

Quantitative measurements on the equilibrium between selenium and iodine 1n ethylene bromide and carbon tetrachloride indicate a compound of formula Se₂I₂, and possibly SeI₄ also.

III.

The Magneto-optic Apparatus was set up according to the directions given by Allison in his numerous publications. The broad minima attributed to the solvent could be located as described, but no minima of the sharp type due to isotopes of the positive ions were observed.

IV.

With the aid of Laue and oscillation photographs, potassium chlorosmate and potassium bromosmate have been shown to have the ammonium chloroplatinate structure. The edge of the unit cube was found to be 9.729 ± 0.02 Å for potassium chlorosmate and 10.30 ± 0.03 Å for potassium bromosmate. The halogen parameters were found to be 0.243 ± 0.002 and 0.244 ± 0.001 respectively. These values give an osmium-chlorine separation of 2.36 ± 0.02 Å and an osmium-bromine separation of 2.51 ± 0.01 Å in the complexes. Subtracting the normal electron-pair bond radius for the halogen in each case, the octahedral electron pair bond radius for quadrivalent osmium is found to be 1.37 ± 0.02 Å in K₂OsCl₆ and 1.37 ± 0.01 Å in K₂OsBr₆.

Thesis Files