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

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).