Structure of Potassium Hydroxide: An X-Ray and Infrared Study

Abstract

Infrared evidence has been obtained which indicates that the crystal structure of KOH reported in the literature is incorrect. A subsequent x‐ray examination has shown that this is the case and has led to a structure compatible with the infrared spectrum. KOH crystallizes in the monoclinic space group C₂²–P2₁ (chosen over P2₁/m on the basis of the infrared evidence), with two molecules in a cell of dimensions a=3.95, b=4.00, c=5.73 A, β=103.6°. Each potassium atom is surrounded by a distorted octahedron of oxygen atoms. There is an oxygen‐oxygen zigzag chain parallel to the b axis. Stereochemical arguments are advanced to suggest that the hydrogen atoms are near to or lie in the plane of the zigzag oxygen chain; infrared data obtained at —180°C for KOH and KOD are interpreted as supporting the placement of the hydrogen atoms in ordered positions along the chain with the O–H···O bonds (of length 3.35 A) nearly or exactly linear. It is argued that breaking of these hydrogen bonds will lead to the high‐temperature cubic structure of KOH reported in the literature.