The synthesis, crystal structure and complexation of a new octacoordinate hexaazamacrocyclic ligand

A new dinucleating 28-membered hexaazadiphenol macrocyclic ligand 3,7,11,19,23,27-hexaaza-33,34-dihydroxy-15,31-dimethyl-tricyclo-tetratriaconta-1(32),13,15,17(34),29(33),30-hexaene, HDTH, was synthesized by NaBH4 hydrogenation of the corresponding Schiff base obtained from the [2+2] condensation between 3,3′-iminobis(propylamine) and diformyl-p-cresol. The structure of its hexahydro-bromide salt, HDTH·6HBr·2CH3OH was determined as a colorless plate crystallizing in the space group P1̄ as a triclinic crystal with the cell dimensions: a=8.5996(4), b=11.0578(5), c=11.8011(5) Å, α=94.2830(10)°, β=100.5330(10)°, γ=101.1380(10)°, V=1075.45(8) Å3, and Z=1. The protonation constants of HDTH and the stability constants of its complexes with Cu(II), Zn(II), Ni(II), Cd(II), Fe(II), Mn(II) and Fe(III) in 1:1 and 2:1 systems (metal–HDTH), have been determined potentiometrically at 25.0 °C and μ=0.100 mol l−1 KCl. Potentiometric equilibrium studies indicate that a variety of deprotonated and protonated mononuclear and dinuclear, as well as hydroxy-bridged complexes, form in the pH range 2–12 in aqueous solution. The species distributions and the characteristics of these complexes are also described.