Synthesis and characterization of alkoxo-oxygen-bridged copper(II) complexes having disc- and rod-like shapes

A series of copper(II) complexes with tridentate Schiff bases, obtained by the 1:1 condensation of a 4-(p-n-alkoxybenzoyloxy)salicylaldehyde and an aminoalcohol have been prepared and characterized, where the n-alkoxy group is n-propyloxy, n-butyloxy, n-hexyloxy, n-octyloxy, n-hexadecyloxy or n-octadecyloxy and the aminoalcohol is 2-aminoethanol, 3-aminopropanol, (R)- or (S)-2-amino-4-methylpentanol. The nineteen complexes thus synthesized can be classified into two groups, A and B; group A contain a 3-aminopropanol residue and B one of the remaining aminoalcohol residues. Group A members are reddish violet and almost diamagnetic, and it is deduced that these molecules are rod-like in shape and involve a binuclear Cu2O2 central core; group B are blue and paramagnetic, and likely to have a tetranuclear Cu4O4 central core of cubane-like structure and overall disc-like molecular shape. Polarized microscopic, differential scanning calorimetry, and heating X-ray diffractometry measurements were made to study the thermotropic mesomorphism. Polymorphic transitions have been characterized for representative complexes from groups A and B.