1. E. Schudt and G. Wertz, Structure Data of Organic Crystals, Part A, Landolt-Börnstein: Numerical Data and Functional Relationships in Science and Technology, New Series, Group III, Vol. 5, Springer Verlag, Berlin, 1971, pp 342–343.
2. A. Rye and H. Sorum, Acta Chem. Scand., 6 (1952) 1128–1129.
3. L.W. Levy, C. R. Acad. Sc. Paris, Ser. C., 267 (1968) 1779–1782.
4. H.M. Berman, G.A. Jeffrey, and R.D Rosenstein., Acta Cryst., B24 (1968) 442–449.
5. H.S. Kim, G.A. Jeffrey, and R.D. Rosenstein, Acta Cryst., B24 (1968) 1449–1455.