Ligand structures binucleating ligands

X-ray crystallographic structures of synthetic dinickel(II) complexes with bound urea have become available for several systems within the last decade, mostly based on the binucleating ligand scaffolds introduced in Section ll.B. 

A good structural and functional model of the heme/nonheme di-iron center of the active site of the prototype NOR has been developed and characterized by Karlin and co-workers.The complexes consist of a binucleating ligand with a tetradentate tris(2-pyridylmethyl)amine moiety tethered to a synthetic tetraarylporphyrin (with three 2,6-difluorophenyl meso substituents see Figure 11). As discussed above, the resonance Raman spectra of the oxidized compound show features in common with NOR supporting the assignment of the active site as oxo-bridged in the oxidized enzyme. 

Related structures to the binucleating crown (206), in which three or four individual macrocycles are linked by spiro-groups, have been synthesized (Weber, 1979 Weber, 1982). Other ligands of this general type, showing a variety of topological arrangements, are also known (Weber ... 

There are only scarce data available on the spatial and electronic structure of these types of clathrochelates, except for the papers describing the complexes with the binucleating trom and azineoximate ligands and the iron(II) and cobalt(III) complexes with hexaene and oximehydrazonate clathrochelate ligands. In all other publications, the data obtained by physical methods have been used mainly to confirm the composition of compounds. 

The crystal and molecular structure of the macrobicyclic heteronuclear [FeCo(trom)](BF4) complex with the encapsulated high-spin Fe2+ and Co ions in the strongly distorted coordination polyhedra, intermediate between a TP and a TAP, was described in Ref 192. The X-ray powder diffraction patterns obtained for other hetero- and homobinuclear complexes of the binucleating trom ligand confirmed that they are isomorphic to heterobinu clear... 

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