Competing large and small angles in a double end-on azido copper(II) Binuclear complex: A combined experimental and theoretical study of magnetic interactions

The structure and magnetic properties of double azidobridged Cu ^II binuclear complex 1 with the chelating chiral ligand (S,S)-2,2'-isopropylidenebis(4-phenyl-2-oxazoline) were analyzed by combining experimental and theoretical techniques. The Cu^II ions adopt: a square pyramidal geometry with different degrees of distortion, whereas the two endon azido bridges disposed at the equatorial positions exhibit significantly different Cu-N-Cu angles, 110.6 and 97,3°, which are respectively smaller and larger than the critical 108° value distinguishing the ferromagnetic and antiferromagnetic regimes, The asymmetry in 1 arises from, the use of the bulky asymmetric ligand, giving rise to two different magnetic pathways between the Cu¹¹ ions, The magnetic pathway along the large Cu-N-Cu angle value dominates over the small one, resulting in a net antiferromagnetic behavior with J = -78,6 cm^-1, On the basis of wavefunction calculations, we investigate the exchange interactions in synthetic compound 1 and fictitious analogs 2 and 3 holding either two large (i.e., 110.6°) or two small (i.e., 97.3°) Cu-NCu angles, The calculated exchange interaction in 1 (-1.04 cm^-1) is in relatively good agreement with the experimental value and corresponds precisely to the average between the antiferromagnetic value in 2 (-218 cm^-1) and the ferromagnetic one in 3 (21 cm^-1). The significant enhancement in the antiferromagnetic contribution accompanying the expansion of one of the Cu-N-Cu bridging angles is undoubtedly the driving force for the observed antiferromagnetic behavior in 1. The control of the local metal environments allowed us to monitor the exchange coupling interactions.