1. For a recent review, see: Mckervey, M. A.; Weill, M.-J. S.; Neu, F. A. in Atwood, J. L.; Davies, J. E. D.; Macnicol, D. D.; Vögtle, F. (Vol. Eds.), Comprehensive Supramolecular Chemistry; Pergamon: UK, 1996; Vol. 1, Chapters 2 and 3.
2. Shannon, R. D. Acta Crystallogr. A, 1976, 32, 751.
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4. Simon, W.; Morf, W. E.; Meier, P. C. In Structure and Bonding; Marcel Dekker: 1973; Vol. 16, p. 113.
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