Lacunar cyclidene complexes of nickel(II) and cobalt(II) containing a misoriented pendant base: synthesis and characterization of a new T-form hemoglobin model

A new model for the T-form of hemoglobin has been developed; it consists of a cobalt(II) complex with a pentadentate ligand in which the binding of the axial ligand is inhibited by a steric device. The compounds reported here are isomeric lacunar cyclidene complexes containing a pyridyl group covalently attached to the macrocycle. One isomer possesses a stereochemistry suitable for the intramolecular coordination of the pyridine nitrogen, as demonstrated by ESR experiments on the cobalt(II) complex. A crystal structure is reported for one of the isomers: (hexamethyl-23-[2-(1-methylpyridiniumyl)] hexaazabicyclo[10.7.7]hexacosahexaene-k 4 N) nickel(II) iodide, C 32 H 5 I 3 NiH 2 O, orthorhombic, Pna2 1