Studies of copper(II) and nickel(II) complexation by bis(1,4,7-triazacyclononane) ligands containing alkene and alkyne bridging groups

The copper(II) and nickel(II) complexes of three new 1,2-bis(1,4,7-triazacyclononane) ligands containing unsaturated four carbon bridging groups is studied by continuous variation UV–Vis spectroscopic and pH potentiometric equilibrium experiments. The cis-butene-2 (LC) linked ligand may form monomeric MN6-type complexes while the trans-butene-2 (LT) and butyne-2 (LY) ligands are prevented by their stereochemistry from forming monomeric complexes and form oligomeric complexes. It is determined that the stability of the CuLC2+ complex is not appreciably different from the oligomeric complexes of LT and LY. Single-crystal X-ray structure determinations are made on three square pyramidal Cu2L4+ complexes: [Cu2LCCl4] (1), [Cu2LYCl4] (2), and [Cu2LT(NO3)2(H2O)2](NO3)2 (3). The structure of [Ni2(LC)2](ClO4)4 · 2H2O (4) is a binuclear dimer that contains two nickel(II) ions sandwiched between two ligands, indicating that bis([9]aneN3) ligands with four linker atom chains may form either monomeric or oligomeric structures.