Electronic and Magnetic Study of Polycationic Mn₁₂ Single-Molecule Magnets with a Ground Spin State S = 11

The preparation, magnetic characterization, and X-ray structures of two polycationic Mn12 single-molecule magnets [Mn12O12(bet)16(EtOH)4](PF6)14·4CH3CN·H2O (1) and [Mn12O12(bet)16(EtOH)3(H2O)](PF6)13(OH)·6CH3CN·EtOH·H2O (2) (bet = betaine = (CH3)3N+−CH2−CO2−) are reported. 1 crystallizes in the centrosymmetric P2/c space group and presents a (0:2:0:2) arrangement of the EtOH molecules in its structure. 2 crystallizes in the noncentrosymmetric P4̅ space group with two distinct Mn12 polycations, [Mn12O12(bet)16(EtOH)2(H2O)2]14+ (2A) and [Mn12O12(bet)16(EtOH)4]14+ (2B) per unit cell. 2A and 2B show a (1:1:1:1) distribution of the coordinated solvent molecules. Interestingly, bond valence sum calculations extracted from X-ray diffraction data indicate the presence of two Mn2+ ions in the Mn12 core for both 1 and 2. This finding is confirmed by X-ray absorption spectroscopy (XAS) measurements. A complete magnetic characterization, including subkelvin micro-SQUID magnetometry and inelastic neutron scattering (INS) measurements, permits to extract the parameters of the giant spin Hamiltonian of these polycations. Compared with the archetypal Mn12 acetate, an increase in the value of the ground spin state from S = 10 to S = 11 together with a decrease in the effective energy barrier, is observed for 1 and 2. Such a result is consistent with the reduction of two Mn3+ to the less anisotropic Mn2+ ion in the structures.