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

Five Cu complexes of trinuclear [Cu (L ) (N ) ] (1), one-dimensional chain [Cu (L ) (N ) ]  (2), trinuclear [Cu (L ) (N ) ] (3) and dinuclear [Cu (L ) (N ) Cl ] (4) and [Cu (L ) (N ) Cl ] (5) (L =RCH OR', R=substituted pyrazole or imidazole, R'=Me, Et or nPr) were synthesized by the reaction of CuCl ⋅2 H O, sodium azide with RCH Cl in CH OH, C H OH or n-C H OH. The ether ligands L and L can be alternatively prepared by the alcoholysis of RCH Cl in the presence of sodium azide, whereas the ligands L 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 Cu 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 Cu ions, favoring strong magnetic coupling. The Cu-N -Cu bridging angles in complexes 1-3 are 98.8(2)°-101.6(1)°, leading to ferromagnetic coupling, whereas the Cu-N -Cu angles in complexes 4 and 5 are close to 103°, leading to antiferromagnetic coupling.