SYNTHESIS, CRYSTAL-STRUCTURE AND MAGNETIC-PROPERTIES OF [CU2(BPYM)(N3)4] (BPYM=2,2'-BIPYRIMIDINE)

The compound of formula [Cu2(bpym)(N3)4] (bpym = 2,2'-bipyrimidine) has been synthesized and its crystal structure determined by X-ray diffraction methods. It crystallizes in the monoclinic space group P2(1)/n with cell constants: a=10.071(2), b=6.376(1), c=11.617(2) angstrom and beta=95.93(1)-degrees; V=742.0(2) angstrom3, D (calc., Z=2)=2.029 g cm-3, M(r)=453.4, F(000)=448, lambda (Mo Kalpha)=0.71073 angstrom, mu (Mo Kalpha)=29.1 cm-1 and T=298 K. A total of 2027 reflections was collected over the range 3 less-than-or-equal-to 2theta less-than-or-equal-to 55-degrees; of these, 1723 were unique and 1427 were considered as observed (I > 3sigma(I)) and used in the structural analysis. The final R and R(w) residuals were 0.0275 and 0.0328, respectively. The structure consists of dinuclear Cu(II)2(bpym) units held together by azido groups in such a way to form a 2D polymer. Each copper atom is in a distorted octahedral environment with two nitrogen atoms of bpym and two nitrogen atoms of azide in the equatorial plane and two other nitrogen atoms of azide groups from neighbouring units occupying the axial position. Magnetic susceptibility data as a function of the temperature exhibit a rounded maximum at 160 K evidencing a large antiferromagnetic interaction. The relevant parameters are g-2.17 and J=-178 cm-1 with the interaction Hamiltonian defined as H=-JS1.S2. The singlet-triplet energy gap is compared to that reported for the related cyanato and thiocyanato copper(II) complexes and the influence of the nature of the pseudohalide ligand on the resulting structure is analyzed.