CuII–azide polynuclear complexes of Cu4 building clusters with Schiff-base co-ligands: synthesis, structures, magnetic behavior and DFT studies

Abstract

Three new copper–azido complexes [Cu₄(N₃)₈(L¹)₂]_n (1), [Cu₄(N₃)₆(L²)₂(H₂O)₂] (2), and [Cu₄(N₃)₆(L³)₂]_n (3) [L¹ is the imine resulting from the condensation of pyridine-2-carboxaldehyde with N-methylethylenediamine, HL² and HL³ are the condensation products of 2-hydroxy-3-methoxybenzaldehyde with N,N-diethylethylenediamine and N-ethylethylenediamine respectively] have been synthesized by using 0.5 molar equivalents of the Schiff base ligands with Cu(NO₃)₂·3H₂O and an excess of NaN₃. Single crystal X-ray structures show that the basic unit of these complexes contains very similar Cu^II₄ building blocks. While 1 and 3 have overall 1D structures, 2 forms discrete tetranuclear clusters due to blocking of two coordination sites on the tetranuclear cluster by water molecules. Magnetic susceptibility measurements over a wide range of temperatures exhibit the presence of both antiferromagnetic 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 1–3 to provide a qualitative theoretical interpretation of their overall magnetic behavior.