The crystal structure of selenourea

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Abstract
The trigonal form of selenourea has been examined by x-ray crystallographic methods both at room temperature and at −100°C. The lattice parameters reported by earlier workers have been refined by least squares to a = 15.285(5) Å, c = 13.007(5) Å at 20°C and a = 15.201(5) Å, c = 12.950(5) Å at −100°C. The space group has been confirmed to be P 3 1 or P 3 2 , which requires nine crystallographically distinct SeC(NH 2 ) 2 molecules. The crystal structure was solved using Patterson techniques and difference Fourier syntheses, and was refined by least squares using three-dimensional data obtained at −100°C. The unit cell contains nine three-fold spiral chains which run parallel to c . The similarity of the crystal structure to the urea- and thiourea-hydrocarbon complexes in discussed. Evidence is presented of N–H⋯Se hydrogen bonds, supporting their recent discovery in chemically related compounds.