Trinuclear heterometallic CuII-MnII complexes of a salen type Schiff base ligand: anion dependent variation of phenoxido bridging angles and magnetic coupling

Five new trinuclear heterometallic CuII-MnII 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 CuII and MnII ions, which results in a final ferrimagnetic ground state with spin 3/2 in the CuII-MnII-CuII trinuclear structure. The weakest antiferromagnetic interaction (JCu-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 (JCu-Mn= -26.5 cm-1) is observed for 3 having the largest Cu-O-Mn angle (101.4°). Complexes 1, 4 and 5 show an average Cu-O-Mn angles of 98.2°, 97.6° and 97.7°, respectively, that lead to intermediate antiferromagnetic interactions (JCu-Mn = -9.6, -9.7, -9.3 cm-1 respectively)