Steric and Electronic Influences of Methyl Substitution on Transition-Metal Complexes of Tetrabenzo[,b,f,j,n][1,5,9,13]tetraazacyclohexadecine

Transition-metal complexes of a tetraaza macrocyclic ligand obtained from Schiff base condensations of 2-amino-5-methylbenzaldehyde were synthesized and characterized (M(MeTAAB)²⁺, M = Co³⁺, Ni²⁺, Cu²⁺, Zn²⁺, Pd²⁺, and Pt²⁺). The crystal structure of [Cu(MeTAAB)(NO₃)][NO₃] was determined by using X-ray crystallographic techniques. The complex crystallizes in the space group P2₁/c with unit cell dimensions a = 13.136 (6) Å, b = 17.294 (7) Å, c = 17.391 (4) Å, and β = 127.66 (2)°. The coordination sphere of the copper ion is six-coordinate, N₄O₂, with a symmetrically bidentate nitrate making the overall geometry a bicapped square pyramid. The macrocyclic ligand is, as expected, distinctly saddle shaped, with S₄ symmetry.