Airey,W. et al.
Spectrochimica Acta, Part A: Molecular and Biomolecular Spectroscopy, 1971 , vol. 27, p. 1505 - 1506

Allan,M. et al.
Journal of the Chemical Society, Dalton Transactions: Inorganic Chemistry (1972-1999), 1973 , p. 2675 - 2681