Ladder-like azido-bridged copper(II) complexes: Synthesis, X-ray structure and magnetic study

Two mixed-ligand copper(II) complexes [{Cu(L1)(μ1,3-N3)}{Cu(L)(μ1,3-N3)(μ1,1-N3)}]n (1) [HL1 = 1-(N-ortho-hydroxyacetophenimino)-2,2-dimethyl-aminoethane; L = 2-(dimethylamino)-ethylamine] and [{Cu(L2)(μ1,3-N3)}{Cu(L)(μ1,3-N3)(μ1,1-N3)}]n (2) [HL2 = 1-(N-5-methoxy-ortho-hydroxyacetophenimino)-2,2-dimethyl-aminoethane] have been formed upon addition of aqueous solution of sodium azide to a methanolic solution of copper nitrate trihydrate and corresponding Schiff-base ligands. The ligands, HL1 and HL2 undergo partial hydrolysis of their imine bond during the course of reaction. Both the complexes contain single end-to-end (μ1,3) azido bridged 1D infinite chains (rail) which propagate parallel to the crystallographic b-axis; neighboring chains are interconnected by pairs through double asymmetric end-on (μ1,1) azido bridges (rung) to yield a ladder-like structure. In both complexes, rungs (end-on azido bridges) do not connect copper centers of the chains like in a regular ladder; instead they connect only the alternating copper sites of the 1D chain. In a chain the coordination environment around copper(II) ions are not the same: while the {Cu(L1)(μ1,3-N3)} and {Cu(L2)(μ1,3-N3)} moieties have a penta-coordinated copper(II) center, the copper(II) ion of the neighboring {Cu(L1)(μ1,3-N3)(μ1,1-N3)} or {Cu(L2)(μ1,3-N3)(μ1,1-N3)} moiety has an octahedral coordination environment. The variable temperature (2–300 K) magnetic susceptibility measurements showed that the magnetic interaction between the metal centers in complexes 1 and 2 is dominantly antiferromagnetic. The results of magnetic model are in good agreement with the experimental data.