Cobalt clathrochelates with dioximes

Complexes containing encapsulated metal ions (clathrochelates ) with the formula [M(dioxime)3(BR)2] are known with iron(II) 135, cobalt(ll) 136, cobalt(III) 137, and ruthenium(ll) 138 (Fig. 37) [205-220]. Generally, these macrobicyclic complexes are prepared by template synthesis from a mixture of... 

In the synthesis of the boron-capped cobalt(II) tris-dioximates, ferrocenylboronic acid was also used as a capping agent [43], Reaction of this Lewis acid with anhydrous C0CI2 and dioximes in oxygen-free methanol gave clathrochelate CoNx3(BFc)2 and CoDm3(BFc)2 complexes ... 

In mixed oximesarcophaginate [Co(tamox)]Cl(C104)2-H20 and [Co(tamox-H)]Cl2-3H20 semiclathrochelates whose symmetry resembles a TAP ( 52°), the Co-N(oxime) and Co-N(amine) distances are substantially different (co 1.90-1.91 and ca 1.97-1.98A, respectively). The observed N-0 distance (co 1.90A) in these compounds is appreciably greater than that of clathrochelate cobalt(III) tris-dioximates (ca 1.83A). This may account for unsuccessful attempts to prepare the corresponding clathrochelate complexes via cross-linking with boric and phenylboronic acids [182]. 

The spectra of clathrochelate cobalt(III) tris-dioximates obtained by cross-linking with chromium, nickel, and zinc(II) complexes, alongside the bands assigned to the n-n transitions in dioximate fragments, contained the d-d transition bands from the capping metal ions that masks the corresponding transitions for the central Co3+ ion [46]. 

The fell values for most macrobicyclic tris-dioximates and Ne-nSn-sarcophaginates (n = 2, 3) increase with decreasing E values. The cobalt Se-sarcophaginates and boron-capped tris-benzyldioximates drop out of linear correlation for both low-spin cobalt(II) and cobalt(III) complexes. The lack of this correlation in the first case may be attributed to the absence of structural changes in passing from the cobalt(III) complex to the cobalt(II) complex. In the second case, an increased fen value may be attributed to the special rigidity of hexaphenyl-substituted cobalt clathrochelates. 

The redox reactions of cobalt sarcophaginates with hemerythrin and cytochrome C have aroused particular interest for biochemists [316, 320, 404-406]. The kinetics of the redox reactions and relaxation dynamics of the clathrochelate cobalt tris-dioximates have been discussed in Refs. 407-409. 

For tin(IV) bromide, the halogenide ion detachment apparently takes place much more readily compared with that of SnF4. However, the bulky bromine atom causes steric hindrances due to its interaction with the substituents at the a-dioxime fragments. In particular, attempts to obtain clathrochelate tribromotin-capped cobalt(III) a-benzyldioximate and a-furyldioximate were not successful, whereas the corresponding trichlorotin-capped complexes were obtained [45]. 

The singlet nature of most bands in the IR spectra of cobalt complexes confirmed the Cs symmetry of their molecules. The C=N stretching vibration bands were appreciably shifted and intensified compared with those of the initial dioximes. Only one band of this type was observed for cobalt(III) complexes, and its position and intensity were more affected than those of cobalt(II) clathrochelates. 

The linear trinuclear [NiDm3(ttnFe)2](PF6)2-0.5H2O complex contains two high-spin capping iron(III) ions with configuration 7.37 A apart. The Ni-N bond distance in the coordination polyhedron (2.035 A) is much higher than those in the square-planar Ni(HDm)2 bis-dimethylglioximate (1.85 A), and clathrochelate iron(III) and cobalt (III) dioximates (M-N ca 1.9 A) [80]. 

The quasi-reversible character of these redox reactions indicates that some geometrical changes are taking place without changing the clathrochelate framework. As in the case of trinuclear cobalt complexes, macrobicyclic nickel dioximates are characterized by a high oxidation state stabilization in comparison with other nickel complexes. For example, for Ni(HDm)2 bis-dioximate, two processes (oxidation and reduction) were observed for nickel(II) ion [80],... 

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