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The design and synthesis of high-spin Mn(II)-based single-molecule magnets (SMMs) have not been well developed to a great extent, as compared with a large number of SMMs based on the other first row transition metal complexes. In light of our success in designing Fe(II), Co(II) and Fe(III)-based SMMs with a high coordination number of 8, it is of great interest to design Mn(II) analogues with such a strategy. In this contribution, four Mn(II) compounds, [MnII(Ln)2](ClO4)2 (1–4) were obtained from reactions of neutral tetradentate ligands, L1–L4, with hydrated MnII(ClO4)2 (L1 = 2,9-bis(carbomethoxy)-1,10-phenanthroline, L2 = 2,9-bis(carbomethoxy)-2,2′-dipyridine, L3 = N2,N9-dibutyl-1,10-phenanthroline-2,9-dicarboxamide, L4 = 6,6′-bis(2-(tert-butyl)-2H-tetrazol-5-yl)-2,2′-bipyridine). Their crystal structures have been determined by X-ray crystallography and it clearly shows that the Mn(II) centers in these compounds have an oversaturated coordination number of 8. Their magnetic properties have been investigated in detail; to our surprise, all of these Mn(II) compounds show interesting slow magnetic relaxation behaviors under an applied direct current field, although they have very small negative D values. [ABSTRACT FROM AUTHOR]

A new pair of multifunctional Zn(II)–Dy(III) enantiomers based on the chiral Schiff-base ligands [R,R-ZnLDy(H2O)(NO3)3] (1R2R-ZnDy) and [S,S-ZnLDy(H2O)(NO3)3] (1S2S-ZnDy) (H2L = phenol, 2,2′-[[(1R,2R/1S,2S)-1,2-diphenyl-1,2-ethanediyl]bis[(E)-nitrilomethylidyne]]bis[6-methoxy]) was synthesized and characterized. Magnetic studies indicate that 1R2R-ZnDy behaves as a single-molecule magnet. Enantiomers 1R2R-ZnDy and 1S2S-ZnDy show chiroptical activity and circularly polarized luminescence in the N,N-dimethylformamide (DMF) solution. The chiral Zn(II)–Dy(III) complexes display magnetic circular dichroism signals at room temperature. Accordingly, these complexes will inspire intriguing research on single-molecule magnets with circular polarization of luminescence activity and magneto-optic effects, which will give new clues to design multifunctional molecular magnetic materials. [ABSTRACT FROM AUTHOR]

The first-row transition metal compounds, [MII(L1)2](ClO4)2 (M = Ni (1); Co (2)), have been prepared by treatment of a neutral tetradentate ligand (L1 = N2,N9-dibutyl-1,10-phenanthroline-2,9-dicarboxamide) with metal perchlorate salts in MeOH. Both compounds have been structurally characterized by X-ray crystallography and it was found that the coordination numbers are 6 and 7, respectively. The reaction of 6,6′-bis(2-tbutyl-tetrazol-5-yl)-2,2′-bipyridine (L2) with hydrated FeII(ClO4)2 afforded a 8-coordinate Fe(II) compound, [FeII(L2)2](ClO4)2 (3); however its reaction with hydrated CoII(ClO4)2 resulted in 6-coordinate [CoII(L2)2](ClO4)2. It is interesting to observe field-induced slow magnetic relaxation in the 7-coordinate Co(II) compound 2 and 8-coordinate Fe(II) compound 3, which further supports the validity of designing high coordination number compounds as single-molecule magnets. Direct current magnetic studies demonstrate that 2 has a very large positive D value (56.2 cm−1) and a small E value (0.66 cm−1), indicating easy plane magnetic anisotropy. Consistent with the larger D value, an effective spin-reversal barrier of Ueff = 100 K (71.4 cm−1) is obtained, which is the highest value reported for 7-coordinate Co(II) complexes with a pentagonal bipyramidal geometry. In contrast, 8-coordinate Fe(II) compound 3 exhibits uniaxial magnetic anisotropy. [ABSTRACT FROM AUTHOR]

A pair of structurally-similar and stable 8-coordinate high-spin Fe(II) and Fe(III) compounds have been obtained. Both compounds exhibit field-induced slow magnetic relaxation behaviour. The Fe(III) compound represents the first example of 8-coordinate Fe(III) single-molecule magnets (SMM). [ABSTRACT FROM AUTHOR]