HEMIPORPHYRAZINE, A PORPHYRIN-RELATED MACROCYCLE THAT INDUCES RHOMBICALLY COMPRESSED STEREOCHEMISTRIES - STRUCTURE AND PROPERTIES OF BIS(PYRIDINE)(HEMIPORPHYRAZINATO)NICKEL(II)

The title compound crystallizes in the P2,/c space group with Z = 4, a = 16.418 (7) A, b = 9.727 (4) A, c = 18.632 (6) A, and /3 = 94.59 (3)'. The stereochemistry is rhombically compressed with the unique axis defined by the metal isoindole nitrogen atoms, which are 1.97 A from the nickel ion. The other two Ni-N distances are 2.18 and 2.22 A, for the macrocyclic and adduct pyridine nitrogen atoms, respectively. In agreement with this, the EPR spectrum of the Cu-doped nickel complex is typical of a predominant Iz2) ground state with a strong rhombic component. %her related complexes were investigated by EPR spectroscopy and found to have a qualitatively similar geometry due to the "elliptical" coordination hole of the hemiporphyrazinato ligand.