OBSERVATION OF THE LONGEST FE-N(PYRIDINE) BOND IN AN FEIIN6 CHROMOPHORE - CRYSTAL-STRUCTURE AND H-1 NUCLEAR-MAGNETIC-RESONANCE STUDIES OF [FEL22][CLO4]2 [L2 = YRAZOL-1-YLMETHYL)-6-(PYRAZOL-1-YLMETHYL)PYRIDINE]

The X-ray structural and H-1 NMR spectral properties of a bis(ligand) iron(II) complex of a tridentate pyridylpyrazole ligand L2 [L2 = 2-(3, 5-dimethylpyrazol-1-ylmethyl)-6-(pyrazol-1 -ylmethyl)pyridine] have be en studied. The complex [Fe(L)2(2)][CIO4]2 Crystallizes as yellow pris ms in the monoclinic space group P2(1)/n with a = 14.122(3), b = 13.61 2(3), c = 18.393(4) angstrom, beta = 99.11(3)-degrees, Z = 4, R = 0.05 18 and R' = 0.0634 for 6464 observed reflections. The Fe atom is bound to six nitrogen atoms from two tridentate (N3) heterocyclic ligands. Considerable distortion is observed with the average Fe-N(pyridine) an d Fe-N(pyrazole) distances being 2.274 and 2.173 angstrom respectively . These bond lengths are markedly longer than corresponding lengths fo r complexes of less sterically demanding ligands. As expected, the lig and molecules are not planar, the pyridyl and pyrazole rings being twi sted relative to each other. The 3-methyl substituent induces a steric barrier to co-ordination and also greater inter-ligand repulsions and this is presumably responsible for the accessibility of the quintet s tate for Fe(II). The H-1 NMR spectral measurements in CD3CN reveal tha t its solid-state structure is retained in solution.