SPIN-CROSSOVER COMPLEXES OF IRON(II) WITH AN N-4 TETRADENTATE SCHIFF-BASE LIGAND

Iron(III) complexes of the Schiff base formed from the condensation of 2-aminobenzaldehyde and ethylenediamine, H(2)amben, were prepared by the reaction of H(2)amben with iron(III) halides in acetone. Fe(amben) Cl and Fe(amben)Br.H2O exhibit a spin crossover between the T-2 and (6 )A states as shown by magnetic susceptibility measurements, variable t emperature Mossbauer spectra, and electron spin resonance at 77 K. Str uctural investigation of this ligand system was carried out on the cop per(II) and nickel(II) analogues. Cu(amben) and Ni(amben) are both ort horhombic with space group P2(1)2(1)2(1) (No. 19) and unit cell parame ters and volume of a = 7.744(2), b = 26.486(7), c = 6.9706(8) Angstrom , V = 1429.7(8) Angstrom(3) for Cu(amben) and a = 7.651(1), b = 25.993 (5), c = 7.040(1) Angstrom, V = 1400.1(4) Angstrom(3) for Ni(amben). T he final R values for Cu(amben) (a total of 1515 reflections of which 1246 were classified as observed (I>3.00 sigma(I)) and Ni(amben) (a to tal of 1483 reflections of which 979 were classified as observed) are R = 0.059, R(w) = 0.90 and R = 0.065, R(w) = 0.085, respectively. Both Cu(amben) and Ni(amben) are monomeric and approximately square planar . The large dihedral angles between the phenyl rings of Cu(amben) (26. 7 degrees) and Ni(amben) (27.4 degrees) may be related to the observat ion of spin crossover behavior in the iron(III) complexes.