Synthesis and characterization of μ-nitrido, μ-carbido and μ-oxo dimers of iron octapropylporphyrazineElectronic supplementary information (ESI) available: Experimental details, characterization data. CCDC 1021997-1021999. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c4dt03207a

Three μ-X bridged diiron octapropylporphyrazine complexes having Fe III -O-Fe III , Fe +3.5 -N&z.dbd;Fe +3.5 and Fe IV &z.dbd;C&z.dbd;Fe IV structural units have been prepared and characterized by UV-vis, EPR, X-ray absorption spectroscopy and electrochemical methods. Single crystals of all the complexes were obtained from benzene-acetonitrile and their structures were determined by X-ray diffraction. In contrast to μ-oxo complex ( 6 ), μ-nitrido ( 7 ) and μ-carbido ( 8 ) dimers crystallized with one benzene molecule per two binuclear complex molecules arranged cofacially to the porphyrazine planes at Fe-C benzene distances of 3.435-3.725 Å and 3.352-3.669 Å for 7 and 8 , respectively. The short distances suggest an interaction between the iron sites and the benzene π-system which is stronger in the case of the Fe IV &z.dbd;C&z.dbd;Fe IV unit with a higher Lewis acidity. The Fe-X-Fe angle increases in the sequence 6 - 7 - 8 from 158.52° to 168.5° and 175.10°, respectively, in agreement with the Fe-X bond order. However, the lengths of the Fe-X bonds do not follow this trend: Fe-O = 1.75/1.76 Å > Fe-C = 1.67/1.67 Å > Fe-N = 1.65/1.66 Å indicating unexpectedly long Fe-C bonds. This observation can be explained by back π-donation from the μ-carbido ligand to the Fe-C antibonding orbital thus decreasing the bond order which is confirmed by DFT calculations. The structural and electronic properties of single-atom bridged diiron macrocyclic complexes are determined by the nature of the bridge.