Cation-dependent nuclearity of the copper-azido moiety: synthesis, structure, and magnetic study.

Mono-, di-, and trinuclear copper-azido moieties have been synthesized by varying the size of the countercations. [Bu4N]+ yielded a [Cu2(N3)6]2- copper-azido moiety in [Bu4N]2[Cu2(mu(1,1)-N3)2(N3)4], 1, and [Pr4N]+ yielded a [Cu3(N3)8]2- moiety in {[Pr4N]2[Cu3(mu(1,1)-N3)4(N3)4]}n, 2, in which symmetry-related [Cu3(N3)8]2- moieties are doubly mu(1,1)-azido bridged to form unprecedented infinite zigzag chains parallel to the crystallographic a-axis. In the case of [Et4N]+, the mononuclear species [Et4N]2[Cu(N3)4], 3, has been formed. All complexes have been characterized structurally by single-crystal X-ray analysis: 1, C32H72N20Cu2, triclinic, space group P, a = 10.671(9) A, b = 12.239(9) A, c = 10.591(5) A, alpha = 110.01(4) degrees , beta = 93.91(5) degrees , gamma = 113.28(5) degrees , V = 1160.0(1) A3; 2, C24H56N26Cu3, monoclinic, space group P2(1)/n, a = 8.811(2) A, b = 37.266(3) A, c = 13.796(1) A, beta = 107.05(1) degrees , V = 4330.8(10) A(3); 3, C16H40N14Cu, tetragonal, space group I4/m, a = b = 10.487(1) A, c = 12.084(2) A, V = 1328.9(3) A3. The variable-temperature magnetic susceptibility measurements showed that although the magnetic interaction in [Bu4N]2[Cu2(mu(1,1)-N3)2(N3)4], 1, is antiferromagnetic (J = -36 cm(-1)), it is ferromagnetic in {[Pr4N]2[Cu3(mu(1,1)-N3)4(N3)4]}n, 2 (J = 7 cm(-1)). As expected, the [Et4N]2[Cu(N3)4] complex, 3, is paramagnetic.