The Determination of the Crystal Structure of Potassium Picrate

Author: Bettman, Max

Year: 1952

Degree: Dissertation (Ph.D.)

Advisors: Hughes, Edward Wesley; Donohue, Jerry

Committee Member: Unknown, Unknown

Option: Chemistry; Physics

DOI: 10.7907/1S9K-H086

Abstract

The crystal structure of potassium picrate has been determined and refined to a considerable degree of accuracy by means of x-ray diffraction techniques. Most of the refinement was carried out by the use of least squares methods, by making use of about half of the three dimensional data obtainable from copper Kα radiation.

The benzene ring of the picrate ion is nearly planar, the deviation from planarity being within experimental error. The para nitro group is twisted 6° out of the plane of the benzene ring, apparently due to ionic attraction of the oxygen atoms to neighboring potassium ions. The ortho nitro groups are twisted 27° out of the plane of the benzene ring due to steric hindrance between the phenol oxygen and its two nearest oxygen neighbors in the ortho nitro groups. Chemical bonds of a given species, such as carbon-carbon bonds, show considerable variations in length. All these variations are quite reasonable in the light of well known principles of structural chemistry.

The packing of the structure seems to be largely determined by the ionic attraction between potassium ions and five out of the seven oxygen atoms of each picrate ion. There also exist some rather short van der Waals contacts between neighboring picrate ions.

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