Macrobicyclic iron complexes

The Fe-N bond lengths a, base spacings h (A), bite and distortion jangles (deg), QS and PQS (mms ). and /values (calculated from Eq. (45)) for macrobicyclic iron complexes. 

When macrobicyclic iron(II) dimethylglyoximates and a-benzyldioximates are studied in detail, for acyclic dioximes such as glyoxime, methylglyoxime, phenylglyoxime, and a-furyldioxime, only fluoroboron-, alkylboron-, and arylboron-capped complexes have been obtained by direct template condensation on the Fe2+ ion and by interaction of the corresponding Fe(HD)2Py2 bis-dioximates with BF3 (C2H5)20 in re-butanol [21, 50]. 

The spectral characteristics for tin-, germanium-, and antimony-capped macrobicyclic iron(II) dioximates differ greatly from those of the corresponding boron-capped complexes discussed above. 

Different configurations of boron- and tin-capped complexes are accounted for by essential differences in their structures the geometry of the former approaches a TP, whereas that of the latter is close to a TAP. The distortion angle q> values for macrobicyclic iron(II) oximehydrazonates were predicted from QS values in their Fe Mdssbauer spectra [188], The predicted

[Pg.240]

The direct X-ray diffraction study is undoubtedly the most optimal and informative structural method for all compounds. Unfortunately, no one has obtained crystals of the binuclear iron(II) azineoximates, which are suitable for X-ray crystallography [193], The structure of these complexes was deduced from EXAFS data, which allow one to obtain the function of the radial atom distribution (RAD) and hence to determine coordination numbers and the distances from the encapsulated iron ions to the clathrochelate framework atoms, and from Fe Mdssbauer spectra, which make it possible to predict the distortion angle (p (see above). Macrobicyclic iron(II) tris-dioximates... 

The CTB in the UV-vis spectra of nonmacrocyclic iron(II) oximehydrazonates and their semi- and clathrochelate derivatives (vmax 19 600-20 600 cm-i) occupies an intermediate position between those of macrobicyclic iron(II) tris-dimethylglyoximates and those of clathrochelate complexes with dihydrazone ihz ligand. A CTB maxima in the spectra of clathrochelate complexes are substantially red shifted compared with that in the spectra of the initial semi-clathrochelates [185-187]. 

The redox properties of macrobicyclic iron(II) mono- and binuclear oximehydrazonates and a-dioximates formed by capping with antimony(V) and germanium(IV) triorganyles were studied by cyclic voltammetry [73, 74]. The electrochemical behaviour of these compounds is similar to that of analogous boron- and tin-capped clathrochelates. Oxidation of all mononuclear complexes involves a one-electron process, assigned to the oxidation of encapsulated iron(II) ion to iron(III) ion. This process is electrochemically... 

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... 

Gunter and coworkers have synthesized a lateral macrobicyclic molecule 197 where a phorphyrin ring is capped by a bridging unit which contains a pyridino subunit. This model system for cytochrome c oxidase is in fact a heterodinuclear complex with iron(III) complexed to the porphyrin unit and copper(II) complexed to the lateral pyridino bridge. A series of these complexes have been made with... 

Synthesis of macrobicyclic MDma(BR)2 complexes (where M is nickel (paramagnetic), iron and cobalt ions R is CeHs and re-C4H9) was reported by Umland and coworkers [38]. However, the formation of nickel complexes of this type was not further confirmed. 

The resultant ligand readily formed semiclathrochelate [M(P(Hpox)2(pox))] complexes (where M is nickel, copper, cobalt, or zinc(II) ions) by the interaction of metal salts, e.g., perchlorates, with P Hpox) i ligand either in dry ethanol or in acetonitrile. Attempts to isolate analogous iron(II) and manganese(II) complexes gave no desired results [91, 92]. Direct synthesis of the macrobicyclic... 

Homobinuclear macrobicyclic copper, cobalt, and iron(II) complexes and a heteronuclear iron(II)/cobalt(II) clathrochelate of the [MiM2(trom)] type arise from interaction of a sodium complex of trom ligand with the corresponding metal salts. 

Binuclear clathrochelate iron(II) oximehydrazonates may be synthesized by the main methods used for the synthesis of macrobicycles of this type proposed for clathrochelate tris-dioximates by a direct template reaction on a metal ion the cross-linking of initial nonmacrocyclic complexes a cross-linking group exchange reaction and a ligand modification reaction. The template condensation of a mononuclear complex to a binuclear one followed by the encapsulation of another metal ion and capping reaction may be also used for the preparation of these compounds. The main methods for the synthesis of these complexes are shown in Scheme 88 [193]. 

Macrobicyclic binuclear iron(II) oximehydrazonates were synthesized by encapsulation of initial nonmacrocyclic tris-complexes with boron- and tin-containing Lewis acids and by direct template reactions on the Fe + ion (Scheme 89). 

The QS in the Fe Mdssbauer spectra is determined by the geometry of the iron(II) coordination polyhedron and has been utilized to gain information on the structure of the complexes from the spectral parameter vs structure correlation. Conversely, the data available on the structure of clathrochelates employed for working out a modern version of the partial quadrupole splitting (PQS) concept permits one to obtain absolute PQS values and to analyse the results for macrobicyclic complexes [264, 265]. 

The i/c=N values in IR spectra of the di- and hexachloride clathrochelate precursors are the lowest of all those known so far for clathrochelate iron(II) tris-dioximates. The vc=n bands of both types of dioximate fragments distinctly appeared in the case of partially substituted Cs-nonsymmetric complexes. Alongside the vm-o and vb-o bands of the macrobicyclic framework, the IR spectra of ribbed-functionalized clathrochelates also contained characteristic lines of the substituents in dioximate fragments [65, 68]. 

The UV-vis spectra of most complexes discussed in this section contain intense metal-ligand CTBs in the visible region. In the spectra of iron(II) complexes with macrobicyclic hexaene ligands these bands appear at ca 22 200 cm- e- (6- 8)xl0 moPR cm-i) along... 

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