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Ferrocenium and cobaltocenium form highly stable 1:1 inclusion complexes with the host cucurbit[7]uril. From electronic absorption spectroscopic data the association equilibrium constants for both complexes were found to be larger than 10 6 L/mol. The electrochemical reduction of either guest leads to a modest loss in binding affinity.
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Ong et al. (2003) studied this question.
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