Synthesis, Crystal Structure and Magnetism of a Macrocyclic Binuclear Dicopper(II) Amino Alcohol Complex From a Metal Directed Reaction Involving Formaldehyde and Nitroethane

Abstract

Condensation of the bis (1,5-diaminopentan-3-ol) dicopper (II) ion with formaldehyde and nitroethane in basic methanol yields the macromonocyclic ligand 3,13-dimethyl-3,13-dinitro-1,5,11,15-tetraazaeicosane-8,18-diol as the dicopper (II) complex. The perchlorate salt of the binuclear complex is very strongly antiferromagnetically coupled, with the magnetic properties measured from 10-300 K identifying a singlet-triplet energy gap of -860 cm^-1 and a magnetic moment at room temperature of 0.48 BM. The discrete, binuclear nature of the complex was confirmed by a crystal structure analysis of the nitrite salt, which crystallizes in the monoclinic space group C2/c, a 14.789(6), b 14.560(6), c 12.759(9)Ǻ, β 99.65(4)°, and consists of the centrosymmetric macrocycle containing two copper ions each coordinated by two secondary nitrogen donors and two (shared) RO- groups, with water and nitrite oxygens occupying axial sites. The macrocycle donors and the copper ions are essentially coplanar. The Cu…Cu distance is 3.031(1)Ǻ, with the Cu-O^--Cu angle 103.6(2)°. The nitro (and methyl) groups at extremities of the macrocycle are in anti dispositions.