1. Mclvor RA, Miller RK (1965) Canada Patent 723181
2. Chudek JA, Foster R, Keith S (1989) Gazz Chim Ital 119:51–53
3. Ertas E, Ozturk T, Wallis JD, Watson WH (1998) J Chem Crystallogr 28:409–412
4. Kawai Y, Watanabe T (2002) Japanese Patent 136240829
5. Hu M (2005) Chinese Patent 1594464