Copper(II) complexes of N-protected amino acids: synthesis and spectroscopic, magnetic and structural, properties of bis(N-acetyl-beta-alaninato)diaquacopper(II) dihydrate and tetrakis[-(N-acetyl-beta-alaninato] diaquadicopper(II) dihydrate. A case of structural isomerism.

A blue and a green compound of the type Cu(Ac-beta-ala)2 x2H20 and a green compound of the type [Cu(Ac-beta-ala)2] were prepared and characterized by means of room-temperature electronic and infrared spectroscopy, low- and room-temperature magnetic and EPR measurements and DSC analysis. For the blue and green hydrate compounds the crystal structure was also determined by single-crystal X-ray diffraction methods. In the blue compound the copper environment consists of two centrosymmetrically related carboxylic oxygens and two water molecules in asquare-planar arrangement. Two weak interactions involving the uncoordinated carboxylic oxygen atoms complete thecoordination to a severely distorted tetragonal bipyramid. In the green isomeric compound the structureconsists of centrosymmetric dimeric units. Coordination around each metal atom is elongated octahedrally with the carboxyloxygen atoms at the equatorial sites and a water molecule and a copper atom in the axial positions. The importance ofhydrogen bonding in the packing of the molecules is also discussed. These complexes represent an example of structuralisomerism depending on the influence of the solution media. The spectroscopic and magnetic properties are interpretedon the basis of the crystal structures, in particular the hydrate and anhydrous green compounds, show antiferromagnetic properties.