mu-Nitridodiiron Complexes with Asymmetric [Fe~(IV)ident to N-Fe~(III)]~(4+) and Symmetric [Fe~(IV)=N=Fe~(IV)]~(5+) Structural Elements

摘要

Dinuclear mu-nitiidodiiron complexes with porphyrin or phthalocyanine ligands can be prepared in good yields by the thermolysis or photolysis of the corresponding mononucle-ar azidoiron(III) complexes, with the concomitant loss of N_2. The resulting compounds contain a symmetric, linear [Fe=N=Fe]~(4+) moiety, in which both Fe ions are formally in the oxidation state + 3.5. These complexes exhibit an ESR-active, 5 = 1/2 ground state that results from the intramolecular antiferromagnetic coupling of alow-spin Fe~(III)(d~5) and a low-spin Fe~(IV)(d~4) center. As the Mossbauer spectra, even at low temperatures, show only one quadrupole doublet with isomer shifts ranging from delta=0.08-0.18 mms~(-1), these complexes belong to class III in the Robin andDay classification scheme, with complete delocalization of the excess electron. These complexes can be electrochemically as well as chemically oxidized to yield compounds containing a [Fe~(IV)=N=Fe~(IV)] unit; these compounds, however, have not yet beenstructurally characterized. They exhibit a diamagnetic ground state (S = 0) due to the strong antiferromagnetic coupling of two Fe~(IV) (S = 1) ions. Further oxidation leads to coordinated porphyrin pi-radical cations mu-oxo bridged porphyrin, phthalocyanine, and porphycene and corrole complexes with [Fe~(III)-O-Fe~(III)]~(4+) , [Fe~(35)-O-Fe~(35)]~(5+) , and [Fe~(IV)-O-Fe~(IV)]~(6+) structural units have also been reported, the latter group only recently.