CuII-Azide Polynuclear Complexes of Three Different Building Clusters with the Same Schiff-Base Ligand: Synthesis, Structures, Magnetic Behavior, and Density Functional Theory Studies

Three copper-azido complexes [Cu4(N3)8(L1)2­(MeOH)2]n (1), [Cu4(N3)8(L1)2] (2), and [Cu5(N3)10(L1)2]n (3) [L1 is the imine resulting from the condensation of pyridine-2-carboxaldehyde with 2-(2-pyridyl)­ethylamine] have been synthesized using lower molar equivalents of the Schiff base ligand with Cu­(NO3)2·3H2O and an excess of NaN3. Single crystal X-ray structures show that the basic unit of the complexes 1 and 2 contains CuII4 building blocks; however, they have distinct basic and overall structures due to a small change in the bridging mode of the peripheral pair of copper atoms in the linear tetranuclear structures. Interestingly, these changes are the result of changing the solvent system (MeOH/H2O to EtOH/H2O) used for the synthesis, without changing the proportions of the components (metal to ligand ratio 2:1). Using even lower proportions of the ligand, another unique complex was isolated with CuII5 building units, forming a two-dimensional complex (3). Magnetic susceptibility measurements over a wide range of temperature exhibit the presence of both antiferromagnetic (very weak) and ferromagnetic exchanges within the tetranuclear unit structures. Density functional theory calculations (using B3LYP functional, and two different basis sets) have been performed on the complexes 1 and 2 to provide a qualitative theoretical interpretation of their overall magnetic behavior.