1. 4. Copper
2. B.J. Hathaway, in: G. Wilkinson, R.D. Gillard, J.A. McCleverty, (Eds.). Comprehensive Coordination Chemistry, vol. 5, Pergamon Press, Oxford, 1987, p. 534).
3. Copper
4. B.J. Hathaway, Structure and Bondings. Springer–Verlag, Berlin–Heidelberg 57 (1984) 55.