Pentadentate Crown Thioethers

Relatively little work on this ligand has been reported. In future investigation of reactivity this ligand may well take on considerable importance, since the sixth coordination site is available for interaction with substrate molecules. 

Strain-energy calculations [175] show that [Cu(15S5)] deviates from the simple pattern of the S4 ligands. This result parallels earlier experimental results, which reveal anomalous results for both its stability constant and dissociation rate constants with Cu(II) [36, 149]. As suggested earlier [37], this difference probably 

Resonance Raman measurements indicate that the S atoms in [Cu(15S5)] migrate rapidly between apical and equatorial positions [192]. Presumably the strain evident in the ring pushes this complex well up the potential curve toward the transition state for rearrangement, and thereby facilitates this stereochemical scrambling. 

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