In Situ Formation of Semichelating Ligands: A Strategy for Tuning the Magnetic Coupling in Azide-Bridged Copper(II) Complexes.

Five CuII complexes of trinuclear [Cu3 (L1 )2 (N3 )6 ] (1), one-dimensional chain [Cu5 (L2 )2 (N3 )10 ]n  (2), trinuclear [Cu3 (L3 )2 (N3 )6 ] (3) and dinuclear [Cu2 (L4 )2 (N3 )2 Cl2 ] (4) and [Cu2 (L5 )2 (N3 )2 Cl2 ] (5) (L1-5 =RCH2 OR', R=substituted pyrazole or imidazole, R'=Me, Et or nPr) were synthesized by the reaction of CuCl2 ⋅2 H2 O, sodium azide with RCH2 Cl in CH3 OH, C2 H5 OH or n-C3 H7 OH. The ether ligands L1 and L2 can be alternatively prepared by the alcoholysis of RCH2 Cl in the presence of sodium azide, whereas the ligands L3-5 form in corresponding alcohols without azide. For complexes 1-5, the oxygen atom of the ether ligands is located at the Jahn-Teller axis of CuII with the long CuO separations of 2.377(3)-2.830(3) Å. The nitrogen atoms of bridging azides are located in the equatorial or basal planes of CuII ions, favoring strong magnetic coupling. The Cu-Nazido -Cu bridging angles in complexes 1-3 are 98.8(2)°-101.6(1)°, leading to ferromagnetic coupling, whereas the Cu-Nazido -Cu angles in complexes 4 and 5 are close to 103°, leading to antiferromagnetic coupling.