Tetranuclear Copper(II) Complexes with Simultaneous Phenoxo and Azido Bridges - Synthesis, Structural and Magnetic Studies

Tetradentate Schiff base ligands with multiple coordinaton sites are one of the best choice for the construction of multinuclear metal complexes. Coupled with auxiliary ligands under self assembling conditions, the scope for generating new structures increases manifold due to various structure directing factors in operation. Though, phenoxo or azido bridged copper(II) systems have been investigated thoroughly from structural and magnetic aspects, the literature is scanty with combined phenoxo and azido bridged systems. In a study on the effect of synthetic conditions on the structures generated and associated magnetic properties, two new tetranuclear copper complexes, viz., [Cu₄(L1)₂(μ-N₃)₂(N₃)₂] (1) and [Cu₄(L2)₂(μ-N₃)₂(N₃)₂] (2) where L1=N,N′-Bis(salicylidene)diaminopropane (salpn) and L2=N,N′-Bis(salicylidene)diaminobenzene (salophen) with both phenoxo and azido bridges are reported. The tetranuclear cluster is made of two inversion related dimers built of phenoxo bridged Cu1 and Cu2 with distorted square planar and square pyramidal geometries respectively. These dimers are bridged by symmetrically bridging azides leading to a tetranuclear core. The contrasting magnetic behavior inspite of same coordination environments, antiferromagnetic in 1 (J₁=−2.17 cm⁻¹; J₂=−28.15 cm⁻¹) and ferromagnetic in 2 (J₁=−74.7 cm⁻¹; J₂=146.5 cm⁻¹), is understood in terms of lower bridge angles and closer separation between copper centers in 2 than in 1.