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Abstract

Pigeon blood red powder samples of SnO were synthesized via a soft chemistry route. A precipitate was obtained from a freshly prepared SnCl2 solution containing phosphorus acid by adding ammonia until a pH value of 4.9 is reached. Heating of the mixture at 95 degrees leads after 5 d to microcrystalline powders of red SnO. The crystal structure was solved and refined from X-ray powder diffraction data (Cmc21; a = 5.0045(3) angstrom, b = 5.7457(3) angstrom, c = 11.0485(5) angstrom, Z = 8). Red SnO crystallizes in a new structure type. Characteristic building units are double layers of tin and oxygen atoms. The tin atoms are surrounded by four oxygen atoms with distances ranging from 2.04 angstrom to 2.67 angstrom, and the highly asymmetric coordination around the Sn2+ ions indicates the presence of a stereochemically active lone pair. LMTO band structure calculations show that the red modification of SnO is an insulator. The electronic structures of red SnO and the zero band gap semiconductor black SnO are compared. The lone pairs of the tin atoms are visualized via the electron localization function.