Cu(II)-azide polymers of Cu3 and Cu6 building units: synthesis, structures, and magnetic exchange mechanism

Two new neutral copper-azido polymers [Cu(3)(N(3))(6)(tmen)(2)](n) (1) and [Cu(6)(N(3))(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(NO(3))(2).3H(2)O and an excess of NaN(3). The single crystal X-ray structure shows that in the basic unit of the 1D complex 1, the three Cu(II) ions are linked by double end-on azido bridges with Cu-N(EO)-Cu angles on both sides of the magnetic exchange critical angle of 108 degrees. Complex 2 is a 3D framework of a basic Cu(6) 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.