Cu(II)-azide polynuclear complexes of Cu4 building clusters with Schiff-base co-ligands: synthesis, structures, magnetic behavior and DFT studies.

Three new copper-azido complexes Cu(4)(N(3))(8)(L(1))(2) (1), [Cu(4)(N(3))(6)(L(2))(2)(H(2)O)(2)] (2), and Cu(4)(N(3))(6)(L(3))(2) (3) [L(1) is the imine resulting from the condensation of pyridine-2-carboxaldehyde with N-methylethylenediamine, HL(2) and HL(3) 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(NO(3))(2)·3H(2)O and an excess of NaN(3). Single crystal X-ray structures show that the basic unit of these complexes contains very similar Cu(II)(4) 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.