Structure of potassium hydroxide: An x-ray and infrared study

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.