We report the synthesis of a hybrid nanocatalyst obtained through the immobilization of bio-inspired [{Mn(bpy)(H2O)}(µ-2-MeC6H4COO)2(µ-O){Mn(bpy)(NO3)}]NO3 compound into functionalized, monodispersed, mesoporous silica nanoparticles. The in situ dual functionalization sol–gel strategy adopted here leads to the synthesis of raspberry-shaped silica nanoparticles of ca. 72 nm with a large open porosity with preferential localization of 1,4-pyridine within the pores and sulfobetaine zwitterion on the nanoparticles’ periphery. These nano-objects exhibit improved catalase-mimicking activity in water thanks to the encapsulation/immobilization of the catalytic active complex and high colloidal stability in water, as demonstrated through the dismutation reaction of hydrogen peroxide.
The two new Mn dinuclear compounds [{Mn(HO)(phen)}(μ-4-CHCHCOO)(μ-O)](ClO)·3CHCN·HO (1·3CHCN·HO) and [{Mn(HO)(phen)}(μ-O)(μ-2-BrCHCOO){Mn(NO)(phen)}]NO (2) have been synthesized. Their structural data reveal significant differences in the shape of the coordination octahedron around the Mn ions in both compounds. The different distortions from ideal geometry incite a very different magnetic behavior, affecting both the zero-field splitting parameters of the Mn ions (D and E) and the magnetic interaction between them. Compound 1, with elongation in the monodentate ligand direction, shows antiferromagnetic coupling (ground state S = 0) and local D < 0, while compound 2, with compression in the oxo bridge direction, displays a ferromagnetic interaction (ground state S = 4) and local D > 0. Theoretical CASSCF and DFT calculations corroborate the different magnetic anisotropy and exchange coupling found in both compounds. Moreover, with the help of theoretical calculations, some interesting magneto-structural correlations have been found between the degree of distortion of the coordination octahedra and the magnetic coupling; it becomes more antiferromagnetic when the elongation parameter, Δ, in absolute value is increased.
The crystal structure of Mn(ii) carboxylate with 3-methylbenzoate as a bridging ligand [Mn(3-MeCHCOO)(HO)] shows a rhomboidal layer, where each pair of neighbor Mn(ii) ions are bridged through only one carboxylate group with a syn-anti conformation. The magnetic exchange between neighbor ions is weakly antiferromagnetic (J = -0.52 cm, g = 2.04), and at low temperature the system shows spin canting with T = 3.8 K. Computational studies, based on periodic calculations of the energies of the significant spin states on the magnetic cell and some higher supercells, corroborate the weak AF interaction between the adjacent Mn(ii) ions and preclude the negligible effect of frustration caused by very weak interactions between the non-adjacent ions in the magnetic response of the system. The results provide compelling evidence that the observed spin canting is due to the local coordination geometry of the manganese ions leading to two antiferromagnetically coupled subnets with different axial vectors.
TThe three azobenzenes CN(C6H4)-N=N-(C5H4N) (py-iso), CN(C6H4)-N=N-(C6H4)CN (cyano-iso) and CN(C6H4)-N=N-(C6H4)NC (iso-iso) with good coordinating groups (pyridine, phenylcyano or phenylisocyano) at the ends of the diazenyl unit have been synthesized and fully...
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