Semi-coordination copper complexes

While the range of copper(II) complexes involving Cu—Br bonds (Table 81c) is more limited than those for Cu—Cl bonds (Table 81b), the structures tend to be analogous, with short Cu—Br distances of 2.4 A and long distances of ca. 3.0 A. Simple iodine complexes of the copper(II) ion are unknown, in view of the ready reduction of copper(II) to copper(I) with the liberation of iodine, nevertheless, copper-iodine bonds are formed if the copper(II) ion is stabilized by complex formation, as in [Cu(bipy)2I]I (420),1299 the structure of which involved the first example of five-coordinate copper(II) stereochemistry.1300 Semi-coordinate iodide... 

The behavior of the systems constituted by the unstoppered compound Cu.29, or the semi-rotaxane Cu.30" [112], is related to the fully blocked rotaxane Cu.31, i.e., the same redox couple can be observed. Some variations of peak intensities with the scan rate also indicate an acceleration of the chemical processes as compared to Cu.31. However, additional signals corresponding to the species Cu (MeCN)4 (Ei/2 = +1.02 V) and Cu (6) (6-coordinate state, Ej/2 = —0.41 V) [95-97, 100] reveal that the dethreading process becomes significant and occurs primarily with the copper(II) species. The 6-coordinate complex evidenced by CV originates from the dethreading and coordination of the linear fragments via their tpy units to a copper center. 

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