Co-existence of ferro- and antiferromagnetic interactions in a hexanuclear mixed-valence CoMnMn cluster sustained by a multidentate Schiff base ligand

The successful utilization of the direct synthesis approach yielded the unprecedented hexanuclear complex of formula [Co 2 Mn II 2 Mn IV 2 (L 1 ) 4 Cl 2 ( 3 -O) 2 (dmf) 4 ]2dmf ( 1 ) (H 3 L is the Schiff base derived from the condensation of salicylaldehyde and 3-aminopropane-1,2-diol). Single crystal X-ray analysis revealed that 1 crystallizes in the monoclinic system P 2 1 / c and it contains a rare mixed-valence {Co III 2 Mn II 2 Mn IV 2 ( 2 -O) 8 ( 3 -O) 2 } core where all metal ions are linked through the phenolato and alkoxo groups of the L 3 ligand. Besides the charge balance resulting from the X-ray structure, the oxidation state of the metal ions has been confirmed by XPS spectroscopy. Cryomagnetic studies indicate the coexistence of ferro- (Mn IV Mn II , J 2 = +1.10(3) cm 1 , J 3 = +2.19(3) cm 1 ; Mn II Mn II , j = +0.283(3) cm 1 ) and antiferromagnetic interactions (Mn IV Mn IV , J 1 = 17.31(4) cm 1 ), with the six-coordinate Co III ions being diamagnetic. DFT type calculations were carried out to substantiate these values. The energy diagram for the different spin states using the best-fit parameters shows the occurrence of six low-lying spin states ( S = 05) which are close in energy but clearly separated from the remaining ones, with the ground spin state being S = 5. Complex 1 is found to be the first example where weak ferromagnetic exchange between Mn II ions through the long OMn IV O pathway takes place. An unprecedented mixed-valence Co III 2 Mn II 2 Mn IV 2 cluster has been synthesized. Magnetochemical investigations combined with DFT calculations demonstrate the co-existence of antiferro- and ferromagnetic interactions within the Mn IV 2 Mn II 2 core.