CuII-Azide Polymers of Cu3 and Cu6 Building Units: Synthesis, Structures, and Magnetic Exchange Mechanism

Two new neutral copper-azido polymers [Cu3(N3)6(tmen)2] n (1) and [Cu6(N3)12(deen)2] n (2) [tmen = N,N,N′,N′-tetramethylethylenediamine and deen = N,N′-diethylethylenediamine] have been synthesized by using lower molar equivalents of the chelating diamine ligands with Cu(NO3)2·3H2O and an excess of NaN3. The single crystal X-ray structure shows that in the basic unit of the 1D complex 1, the three CuII ions are linked by double end-on azido bridges with Cu−NEO−Cu angles on both sides of the magnetic exchange critical angle of 108°. Complex 2 is a 3D framework of a basic Cu6 cluster. Cryomagnetic susceptibility measurements over a wide range of temperature exhibit dominant ferromagnetic behavior in both the complexes. Density functional theory calculations (B3LYP functional) have been performed on the trinuclear unit to provide a qualitative theoretical interpretation of the overall ferromagnetic behavior shown by the complex 1.