Synthesis and crystallographic characterisation of pendant-arm macrocyclic complexes derived from 1,4,7-triazacyclononane: mono- and di-(3-aminopropyl)-1,4,7-triazacyclononane as ligands

Abstract

Metal complexes based on pendant-arm ligands derived from triazacyclononane have been prepared and characterised. The ligands 1,4-di(3-aminopropyl)-1,4,7-triazacyclononane (daptacn) and 1-(3-aminopropyl)-1,4,7-triazacyclononane (maptacn) with two and one pendant arms have been complexed to cobalt(III), copper(III) and nickel(II) in the former system and with nickel(II) in the latter. X-Ray studies show the complex [Co(daptacn)Cl][ClO₄]₂·H₂O to crystallise in the orthorhombic space group Pbca with a= 19.538(4), b= 16.813(4) and c= 13.155(3)Å. Refinement converged at R= 0.0855 (R′= 0.0724) for 395 parameters using 1906 reflections with I > σ(I). The complex ion is octahedral with the chloride trans to a tertiary nitrogen donor. The same structure is maintained in solution. Refinement of the complex [Cu(daptacn)][ClO₄]₂(orthorhombic, space group Pbca), with a= 17.358(4), b= 14.262(3) and c= 16.533(4)Å for 253 parameters using 1378 reflections with I > 2σ(I) converged at R= 0.0811 (R′= 0.0895). The complex is square pyramidal with an axial Cu–N bond length of 2.251(12)Å. The tetradentate ligand maptacn forms a dinuclear complex [Ni₂(maptacn)₂(µ-Cl)₂][ClO]₂ in which the remaining octahedral sites are filled by bridging chlorides. The perchlorate salt crystallised in the triclinic space group P with a= 10.235(2), b= 11.373(3), c= 7.150(2)Å, α= 81.84(2), β= 99.36(2) and γ= 109.96(2)°. Refinement converged at R= 0.0562 (R′= 0.0641) for 269 parameters using all 2709 reflections collected. There is strong hydrogen bonding between the N(4) donors of the pendant arms and the counter perchlorate ions. The chloride ions may be replaced by a bridging oxalate group. For this complex, oxidation to nickel(III) takes place yielding an ESR spectrum containing evidence for the unpaired electron in a d_{x²– y²} orbital (g_∥= 2.184, g_⊥= 2.079) but no hyperfine splitting.