Trinuclear heterometallic Cu^II–Mn^II complexes of a salen type Schiff base ligand: anion dependent variation of phenoxido bridging angles and magnetic coupling

Abstract

Five new trinuclear heterometallic Cu^II–Mn^II complexes [(CuL) ₂Mn(O₂CPh)₂] (1), [(CuL) ₂Mn(N₃)₂] (2), [(CuL) ₂Mn(NCO)₂] (3), [(CuL) ₂Mn(NO₃)₂] (4) and [(CuL) ₂Mn(Sal) ₂]•CH₂Cl₂ (5) have been synthesized with the di-Schiff base ligand H₂L (where H₂L = N,N′-bis(salicylidene)-1,3-propanediamine and Sal = salicylate). These complexes with different anionic co-ligands have been synthesized to attain a large variation in phenoxido bridging angles and to investigate its consequence on magnetic properties. Single crystal X-ray diffraction analyses reveal that complexes 1, 2, 4 and 5 are linear, whereas 3 has an angular geometry. Variable temperature magnetic susceptibility measurements suggest that all five complexes possess an overall antiferromagnetic interaction between Cu^II and Mn^II ions, which results in a final ferrimagnetic ground state with spin 3/2 in the Cu^II–Mn^II–Cu^II trinuclear structure. The weakest antiferromagnetic interaction (J_Cu–Mn = −7.0 cm⁻¹) is observed for 2 having the lowest value of the Cu–O–Mn angle (92.0°), while the strongest antiferromagnetic interaction (J_Cu–Mn = −26.5 cm⁻¹) is observed for 3 having the largest Cu–O–Mn angle (101.4°). Complexes 1, 4 and 5 show average Cu–O–Mn angles of 98.2°, 97.6° and 97.7°, respectively, that lead to intermediate antiferromagnetic interactions (J_Cu–Mn = −9.6, −9.7, −9.3 cm⁻¹ respectively).