For single-molecule magnet (SMM) behavior, molecular clusters require Ising magnetoanisotropy (D mol < 0) and a large ground-state spin multiplicity.[1] These requirements result in a high thermal barrier (U) to magnetization relaxation. Such clusters elicit intense interest in both chemistry and physics owing to behavior that is intermediate between that of a simple paramagnet (or classical bulk magnet) and that of a quantum/classical system, [2] which heralds applications in quantum devices.[3] The development of SMMs is often determined by serendipitous assembly. [2,4] However, the synthesis of molecular clusters with SMM-type behaviors presents a formidable challenge because of the difficulties in assembling predetermined structures with predictable magnetic properties. [4] The Mn 12 and Fe 8 clusters and their derivatives [2,4] are the most widely studied of homo-and heterometallic SMM systems, [4][5][6] and only very few cobalt-based SMMs are known. [7] One reason may be the difficulty in synthesizing cobalt clusters that display a large spin and molecular anisotropy. Because Co II has an exceptionally large D ion > 0 (a characteristic known to dominate molecular anisotropy), [8] only a limited number of high-nuclearity clusters are known for cobalt compared with manganese and iron. [4, 7c] Previous investigations implied that an alkoxido-bridged metal-cubane structure probably favors ferromagnetic coupling through m 3 -O bridges, in which orthogonal hard-axis alignment of four single-ion spins (D ion > 0) may result in a negative D mol value for the clusters. [7a, 8] As 2-(hydroxymethyl)pyridine (hmp) can furnish a cubane-like M 4 O 4 motif, [9] we chose the analogous (1H-benzimidazol-2-yl)methanol (Hbm) to serve as a chelating/bridging ligand to bring (Figure 1).[10] The cubane subunit is constructed by four Co II ions and four alkoxido oxygen atoms of m 3 -h 1 :h 3 -bm ligands.The Co1 and Co2 atoms in distorted octahedral N 2 O 4 environments are complexed by two O,N-chelating sites, one bm m 3 -alkoxido oxygen atom, and one EtOH ligand. The Co3 and Co4 atoms both form distorted CoO 6 octahedra with three alkoxido groups, two acetate groups, and one nitrate group. The cuboidal core is distorted with all the Co-O-Co angles in the range (98 AE 4)8 (Table S1 in the Supporting Information) for Co···Co dominant ferromagnetic exchange. [7a,b] Similar to the hmp analogue, the Co···Co distances vary from 3.034 to 3.243 . A Jahn-Teller distortion of the four d 7 Co 2+ ions lowers the symmetry of the cubes to S 4 . In addition to the central m 6 -NO 3 À bridge, six syn-syn acetate ligands also interconnect neighboring cubane units in the supercluster. Five discrete NO 3 À ions balance the overall positive charge of the cluster. There are no significant intermolecular interactions. A space-filling plot of 1 reveals that the cluster has an approximate trefoil shape with a diameter of about 2.0 nm ( Figure S1 in the Supporting Information). High coordination numbers of nitrate, a weak ligand, to transition met...

By using the node-and-spacer approach in suitable solvents, four new heterotrimetallic 1D chain-like compounds (that is, containing 3d-3d'-4f metal ions), {[Ni(L)Ln(NO(3))(2)(H(2)O)Fe(Tp*)(CN)(3)]⋅2 CH(3)CN⋅CH(3)OH}(n) (H(2)L = N,N'-bis(3-methoxysalicylidene)-1,3-diaminopropane, Tp* = hydridotris(3,5-dimethylpyrazol-1-yl)borate; Ln = Gd (1), Dy (2), Tb (3), Nd (4)), have been synthesized and structurally characterized. All of these compounds are made up of a neutral cyanide- and phenolate-bridged heterotrimetallic chain, with a {-Fe-C≡N-Ni(-O-Ln)-N≡C-}(n) repeat unit. Within these chains, each [(Tp*)Fe(CN)(3)](-) entity binds to the Ni(II) ion of the [Ni(L)Ln(NO(3))(2)(H(2)O)](+) motif through two of its three cyanide groups in a cis mode, whereas each [Ni(L)Ln(NO(3))(2)(H(2)O)](+) unit is linked to two [(Tp*)Fe(CN)(3)](-) ions through the Ni(II) ion in a trans mode. In the [Ni(L)Ln(NO(3))(2)(H(2)O)](+) unit, the Ni(II) and Ln(III) ions are bridged to one other through two phenolic oxygen atoms of the ligand (L). Compounds 1-4 are rare examples of 1D cyanide- and phenolate-bridged 3d-3d'-4f helical chain compounds. As expected, strong ferromagnetic interactions are observed between neighboring Fe(III) and Ni(II) ions through a cyanide bridge and between neighboring Ni(II) and Ln(III) (except for Nd(III) ) ions through two phenolate bridges. Further magnetic studies show that all of these compounds exhibit single-chain magnetic behavior. Compound 2 exhibits the highest effective energy barrier (58.2 K) for the reversal of magnetization in 3d/4d/5d-4f heterotrimetallic single-chain magnets.

A series of seven-coordinate mononuclear lanthanide(III) complexes of the general formula [(TPP)Ln(L(OEt))]·0.25H2O and [(Pc)Ln(L(OEt))] (Ln(3+) = Dy(3+), Tb(3+), Ho(3+), and Gd(3+); TPP = 5,10,15,20-tetraphenylporphyrinate; Pc = phthalocyaninate; L(OEt)(-) = [(η(5)-C5H5)Co(P(=O)(OEt)2)3](-)) are synthesized on the basis of the tripodal ligand L(OEt)(-) and either porphyrin or phthalocyanine ligands. All of the complexes are characterized by X-ray crystallography and by static and dynamic magnetic measurements. The Dy and Tb complexes show the field-induced slow relaxation of magnetization, and they are interesting seven-coordinate single-lanthanide-based SMMs. The magnetic relaxation properties of these double-decker sandwich complexes are influenced by the local molecular symmetry and are sensitive to subtle distortions of the coordination geometry of the paramagnetic lanthanide ions, such as metal-to-plane distances, plane center distances, and bending angles.

Four couples of enantiomerically pure chiral seven-coordinated mononuclear lanthanide complexes, [(L(OEt))Dy((R,R)-Salphen)](2)·3H(2)O (1, L(OEt) = [(Cp)Co(P(O)(OEt)(2))(3)], Cp = cyclopentadiene, Salphen = N,N'-1,2-diphenylethylenebis(salicylideneiminato) dianion), [(L(OEt))Dy((S,S)-Salphen)](2)·3H(2)O (2), [(L(OEt))Dy((R,R)-5-Cl-Salcy)]·CH(3)OH·1/8H(2)O (3, Salcy = N,N'-(1,2-cyclohexanediylethylene)bis(salicylideneiminato) dianion), [(L(OEt))Dy((S,S)-5-Cl-Salcy)]·CH(3)OH·1/8H(2)O (4), [(L(OEt))Tb((R,R)-5-Cl-Salcy)]·CH(3)OH·1/8H(2)O (5), [(L(OEt))Tb((S,S)-5-Cl-Salcy)]·CH(3)OH·1/8H(2)O (6), [(L(OEt))Ho((R,R)-5-Cl-Salcy)]·CH(3)OH·1/8H(2)O (7) and [(L(OEt))Ho((S,S)-5-Cl-Salcy)]·CH(3)OH·1/8H(2)O (8), have been successfully synthesized by using tetradentate chiral salen-type ligands and the Kläui's tripodal ligand of L(OEt). Structural analyses reveal that all compounds have a typical double-decker sandwich structure, and the Ln(iii) ions exhibit a rare seven-coordinated mode, situating in a distorted monocapped triangular prism polyhedron. Circular dichroism (CD) spectra confirm the enantiomeric nature of the optically active complexes and demonstrate that the chirality is successfully transferred from the ligand to the coordination environment of the Ln(iii) ions. Field-induced slow relaxation of the magnetization is observed for complexes 1-4, suggesting that they can be rare chiral single-ion magnets (SIMs) based on the seven-coordinated lanthanide ions.