Magnetic and spectroscopic behavior of amine adducts of copper(II) N-acetyl -beta-alaninate

A series of ternary complexes with the general formula Cu(ac-β-ala)2B2·nH2O (ac-β-ala = N-acetyl-β-alaninate ion;n = 0 and B = ethylenediamine (en), 4-methylpyridine (4pic); n = 2 and B = pyridine (py) and 4pic) and Cu(ac-β-ala)2B(B = piperazine (pipz), 2,2′-bipyridine (bipy), py, 3-methylpyridine (3pic), 4pic) were synthesized and investigated by means of infrared, electronic, e.p.r. spectroscopy and variable temperature magnetic measurements. The green monoamine adducts of py, 3- and 4pic (pKa⩽ 6) showed physical properties which indicated a binuclear geometry as in the parent complex [Cu(ac-β-ala)2·H2O]2·2H2O. The |2J| values of these adducts increased with respect to the hydrate complex, and were comparable to those of carboxylic acids of similar complexity. For this type of complexes the narrow spectral range of v(OCO)as and v(OCO)s indicates only slight dependence on N-protected amino acids. The blue or violet monomeric compounds display spectroscopic properties which indicate a tetragonal configuration whose distortion increases with the basic strength of the amine. For en derivatives all the experimental results are in accord with a square geometry with CuN4 chromophore, the amino acid acting only as a counterion.