Single-Molecule Magnets of Ferrous Cubes: Structurally Controlled Magnetic Anisotropy

Tetranuclear FeII cubic complexes were synthesized with Schiff base ligands bridging the FeII centers. X-ray structural analyses of six ferrous cubes, [Fe4(sap)4(MeOH)4]·2H2O (1), [Fe4(5-Br-sap)4(MeOH)4] (2), [Fe4(3-MeO-sap)4(MeOH)4]·2MeOH (3), [Fe4(sae)4(MeOH)4] (4), [Fe4(5-Br-sae)4(MeOH)4]·MeOH (5), and [Fe4(3,5-Cl2-sae)4(MeOH)4] (6) (R-sap and R-sae were prepared by condensation of salicylaldehyde derivatives with aminopropyl alcohol and aminoethyl alcohol, respectively) were performed, and their magnetic properties were studied. In 1−6, the alkoxo groups of the Schiff base ligands bridge four FeII ions in a μ3-mode forming [Fe4O4] cubic cores. The FeII ions in the cubes have tetragonally elongated octahedral coordination geometries, and the equatorial coordination bond lengths in 4−6 are shorter than those in 1−3. Dc magnetic susceptibility measurements for 1−6 revealed that intramolecular ferromagnetic interactions are operative to lead an S = 8 spin ground state. Analyses of the magnetization data at 1.8 K gave the axial zero-field splitting parameters (D) of +0.81, +0.80, +1.15, −0.64, −0.66, and −0.67 cm-1 for 1−6, respectively. Ac magnetic susceptibility measurements for 4−6 showed both frequency dependent in- and out-of-phase signals, while 1−3 did not show out-of-phase signals down to 1.8 K, meaning 4−6 are single-molecule magnets (SMMs). The energy barriers to flip the spin between up- and down-spin were estimated to 28.4, 30.5, and 26.2 K, respectively, for 4−6. The bridging ligands R-sap2- in 1−3 and R-sae2- in 4−6 form six- and five-membered chelate rings, respectively, which cause different steric strain and Jahn−Teller distortions at FeII centers. The sign of the D value was discussed by using angular overlap model (AOM) calculations for irons with different coordination geometry

Antiferromagnetic Fe^III₆ Ring and Single-Molecule Magnet Mn^II₃Mn^III₄ Wheel

Reactions of a quadridentate ligand [N-(2-hydroxy-5-nitrobenzyl)iminodiethanol] with iron and manganese chloride in methanol yielded an antiferromagnetic FeIII6 ring and a single-molecule magnet MnII3MnIII4 wheel, respectively

Single-Molecule Magnets of Ferrous Cubes: Structurally Controlled Magnetic Anisotropy

Tetranuclear FeII cubic complexes were synthesized with Schiff base ligands bridging the FeII centers. X-ray structural analyses of six ferrous cubes, [Fe4(sap)4(MeOH)4]·2H2O (1), [Fe4(5-Br-sap)4(MeOH)4] (2), [Fe4(3-MeO-sap)4(MeOH)4]·2MeOH (3), [Fe4(sae)4(MeOH)4] (4), [Fe4(5-Br-sae)4(MeOH)4]·MeOH (5), and [Fe4(3,5-Cl2-sae)4(MeOH)4] (6) (R-sap and R-sae were prepared by condensation of salicylaldehyde derivatives with aminopropyl alcohol and aminoethyl alcohol, respectively) were performed, and their magnetic properties were studied. In 1−6, the alkoxo groups of the Schiff base ligands bridge four FeII ions in a μ3-mode forming [Fe4O4] cubic cores. The FeII ions in the cubes have tetragonally elongated octahedral coordination geometries, and the equatorial coordination bond lengths in 4−6 are shorter than those in 1−3. Dc magnetic susceptibility measurements for 1−6 revealed that intramolecular ferromagnetic interactions are operative to lead an S = 8 spin ground state. Analyses of the magnetization data at 1.8 K gave the axial zero-field splitting parameters (D) of +0.81, +0.80, +1.15, −0.64, −0.66, and −0.67 cm-1 for 1−6, respectively. Ac magnetic susceptibility measurements for 4−6 showed both frequency dependent in- and out-of-phase signals, while 1−3 did not show out-of-phase signals down to 1.8 K, meaning 4−6 are single-molecule magnets (SMMs). The energy barriers to flip the spin between up- and down-spin were estimated to 28.4, 30.5, and 26.2 K, respectively, for 4−6. The bridging ligands R-sap2- in 1−3 and R-sae2- in 4−6 form six- and five-membered chelate rings, respectively, which cause different steric strain and Jahn−Teller distortions at FeII centers. The sign of the D value was discussed by using angular overlap model (AOM) calculations for irons with different coordination geometry

Rotational Motion and Nuclear Spin Interconversion of H₂O Encapsulated in C₆₀ Appearing in the Low-Temperature Heat Capacity

The heat capacity of H2O encapsulated in fullerene C60 is determined for the first time at temperatures between 0.6 and 200 K. The water molecule in H2O@C60 undergoes quantum rotation at low temperature, and the ortho-H2O and para-H2O isomers are identified by labeling the rotational energy levels with the nuclear spin states. A rounded heat capacity maximum is observed at ∼2 K after rapid cooling due to splitting of the rotational JKaKc = 101 ground state of ortho-H2O. This anomalous feature decreases in magnitude over time, reflecting the conversion of ortho-H2O to para-H2O. Time-dependent heat capacity measurements at constant temperature reveal three nuclear spin conversion processes: a thermally activated transition with Ea ≈ 3.2 meV and two temperature-independent tunneling processes with time constants of τ1 ≈ 1.5 h and τ2 ≈ 11 h

Coordination-Tuned Single-Molecule-Magnet Behavior of Tb^III−Cu^II Dinuclear Systems

TbIII−CuII-based single-molecule magnet (SMM) and non-SMM were synthesized to investigate the relationship between magnetic anisotropy and the symmetry of the ligand field by the reaction of [TbCu(o-vanilate)2(NO3)3] with methoxypropylamine (MeOC3H6NH2, 1) or ethoxyethylamine (EtOC2H4NH2, 2). In both complexes, TbIII ions have a bicapped square-antiprism coordination geometry. When the TbIII ion is in a less symmetrical ligand field, it has an easy-axis anisotropy and shows SMM behavior, whereas when it is in a more symmetrical environment, it has an easy-plane anisotropy and exhibits non-SMM behavior

Single-Molecule Magnets of Ferrous Cubes: Structurally Controlled Magnetic Anisotropy

Tetranuclear FeII cubic complexes were synthesized with Schiff base ligands bridging the FeII centers. X-ray structural analyses of six ferrous cubes, [Fe4(sap)4(MeOH)4]·2H2O (1), [Fe4(5-Br-sap)4(MeOH)4] (2), [Fe4(3-MeO-sap)4(MeOH)4]·2MeOH (3), [Fe4(sae)4(MeOH)4] (4), [Fe4(5-Br-sae)4(MeOH)4]·MeOH (5), and [Fe4(3,5-Cl2-sae)4(MeOH)4] (6) (R-sap and R-sae were prepared by condensation of salicylaldehyde derivatives with aminopropyl alcohol and aminoethyl alcohol, respectively) were performed, and their magnetic properties were studied. In 1−6, the alkoxo groups of the Schiff base ligands bridge four FeII ions in a μ3-mode forming [Fe4O4] cubic cores. The FeII ions in the cubes have tetragonally elongated octahedral coordination geometries, and the equatorial coordination bond lengths in 4−6 are shorter than those in 1−3. Dc magnetic susceptibility measurements for 1−6 revealed that intramolecular ferromagnetic interactions are operative to lead an S = 8 spin ground state. Analyses of the magnetization data at 1.8 K gave the axial zero-field splitting parameters (D) of +0.81, +0.80, +1.15, −0.64, −0.66, and −0.67 cm-1 for 1−6, respectively. Ac magnetic susceptibility measurements for 4−6 showed both frequency dependent in- and out-of-phase signals, while 1−3 did not show out-of-phase signals down to 1.8 K, meaning 4−6 are single-molecule magnets (SMMs). The energy barriers to flip the spin between up- and down-spin were estimated to 28.4, 30.5, and 26.2 K, respectively, for 4−6. The bridging ligands R-sap2- in 1−3 and R-sae2- in 4−6 form six- and five-membered chelate rings, respectively, which cause different steric strain and Jahn−Teller distortions at FeII centers. The sign of the D value was discussed by using angular overlap model (AOM) calculations for irons with different coordination geometry

Antiferromagnetic Fe^III₆ Ring and Single-Molecule Magnet Mn^II₃Mn^III₄ Wheel

Reactions of a quadridentate ligand [N-(2-hydroxy-5-nitrobenzyl)iminodiethanol] with iron and manganese chloride in methanol yielded an antiferromagnetic FeIII6 ring and a single-molecule magnet MnII3MnIII4 wheel, respectively

Single-Molecule Magnets of Ferrous Cubes: Structurally Controlled Magnetic Anisotropy

Tetranuclear FeII cubic complexes were synthesized with Schiff base ligands bridging the FeII centers. X-ray structural analyses of six ferrous cubes, [Fe4(sap)4(MeOH)4]·2H2O (1), [Fe4(5-Br-sap)4(MeOH)4] (2), [Fe4(3-MeO-sap)4(MeOH)4]·2MeOH (3), [Fe4(sae)4(MeOH)4] (4), [Fe4(5-Br-sae)4(MeOH)4]·MeOH (5), and [Fe4(3,5-Cl2-sae)4(MeOH)4] (6) (R-sap and R-sae were prepared by condensation of salicylaldehyde derivatives with aminopropyl alcohol and aminoethyl alcohol, respectively) were performed, and their magnetic properties were studied. In 1−6, the alkoxo groups of the Schiff base ligands bridge four FeII ions in a μ3-mode forming [Fe4O4] cubic cores. The FeII ions in the cubes have tetragonally elongated octahedral coordination geometries, and the equatorial coordination bond lengths in 4−6 are shorter than those in 1−3. Dc magnetic susceptibility measurements for 1−6 revealed that intramolecular ferromagnetic interactions are operative to lead an S = 8 spin ground state. Analyses of the magnetization data at 1.8 K gave the axial zero-field splitting parameters (D) of +0.81, +0.80, +1.15, −0.64, −0.66, and −0.67 cm-1 for 1−6, respectively. Ac magnetic susceptibility measurements for 4−6 showed both frequency dependent in- and out-of-phase signals, while 1−3 did not show out-of-phase signals down to 1.8 K, meaning 4−6 are single-molecule magnets (SMMs). The energy barriers to flip the spin between up- and down-spin were estimated to 28.4, 30.5, and 26.2 K, respectively, for 4−6. The bridging ligands R-sap2- in 1−3 and R-sae2- in 4−6 form six- and five-membered chelate rings, respectively, which cause different steric strain and Jahn−Teller distortions at FeII centers. The sign of the D value was discussed by using angular overlap model (AOM) calculations for irons with different coordination geometry

Preparation and Properties of Cyclopentadienyl- and Pentamethylcyclopentadienyl−Titanium(IV) Complexes with the C₈H₄S₈ Ligand, Electrical Conductivities of Their Oxidized Species, and X-ray Crystal Structure of Ti(C₅Me₅)₂(C₈H₄S₈)

Ti(C5H5)2(C8H4S8) (1), Ti(C5Me5)2(C8H4S8) (2), [NMe4][Ti(C5H5)(C8H4S8)2] (3), and [NMe4][Ti(C5Me5)(C8H4S8)2] (4) [C8H4S82- = 2-{(4,5-ethylenedithio)-1,3-dithiole-2-ylidene}-1,3-dithiole-4,5-dithiolate(2−)] were prepared by reaction of Ti(C5H5)2Cl2, Ti(C5Me5)2Cl2, Ti(C5H5)Cl3, or Ti(C5Me5)Cl3 with Li2C8H4S8 or [NMe4]2[C8H4S8] in THF. They were oxidized by iodine, the ferrocenium cation, or TCNQ (7,7,8,8-tetracyano-p-quinodimethane) in CH2Cl2 or in acetone to afford one-electron-oxidized and over-one-electron-oxidized species, [Ti(C5H5)2(C8H4S8)]·I3, [Ti(C5H5)2(C8H4S8)][PF6], [Ti(C5Me5)2(C8H4S8)]·I3, [Ti(C5Me5)2(C8H4S8)][PF6], [Ti(C5H5)(C8H4S8)2]·I0.9, [Ti(C5H5)(C8H4S8)2][TCNQ]0.3, [Ti(C5Me5)(C8H4S8)2]·I2.4, and [Ti(C5Me5)(C8H4S8)2][TCNQ]0.3, with the C8H4S8 ligand-centered oxidation. They exhibited electrical conductivities of 1.6 × 10-1 to 7.6 × 10-4 S cm-1 measured for compacted pellets at room temperature. The crystal structure of 2 was clarified to consist of isolated dimerized units of the molecules through some sulfur−sulfur nonbonded contacts:  monoclinic, P21/c, a = 9.534(2) Å, b = 18.227(2) Å, c = 17.775(2) Å, β = 94.39(1)°, Z = 4

Single-Molecule Magnets of Ferrous Cubes: Structurally Controlled Magnetic Anisotropy

Tetranuclear FeII cubic complexes were synthesized with Schiff base ligands bridging the FeII centers. X-ray structural analyses of six ferrous cubes, [Fe4(sap)4(MeOH)4]·2H2O (1), [Fe4(5-Br-sap)4(MeOH)4] (2), [Fe4(3-MeO-sap)4(MeOH)4]·2MeOH (3), [Fe4(sae)4(MeOH)4] (4), [Fe4(5-Br-sae)4(MeOH)4]·MeOH (5), and [Fe4(3,5-Cl2-sae)4(MeOH)4] (6) (R-sap and R-sae were prepared by condensation of salicylaldehyde derivatives with aminopropyl alcohol and aminoethyl alcohol, respectively) were performed, and their magnetic properties were studied. In 1−6, the alkoxo groups of the Schiff base ligands bridge four FeII ions in a μ3-mode forming [Fe4O4] cubic cores. The FeII ions in the cubes have tetragonally elongated octahedral coordination geometries, and the equatorial coordination bond lengths in 4−6 are shorter than those in 1−3. Dc magnetic susceptibility measurements for 1−6 revealed that intramolecular ferromagnetic interactions are operative to lead an S = 8 spin ground state. Analyses of the magnetization data at 1.8 K gave the axial zero-field splitting parameters (D) of +0.81, +0.80, +1.15, −0.64, −0.66, and −0.67 cm-1 for 1−6, respectively. Ac magnetic susceptibility measurements for 4−6 showed both frequency dependent in- and out-of-phase signals, while 1−3 did not show out-of-phase signals down to 1.8 K, meaning 4−6 are single-molecule magnets (SMMs). The energy barriers to flip the spin between up- and down-spin were estimated to 28.4, 30.5, and 26.2 K, respectively, for 4−6. The bridging ligands R-sap2- in 1−3 and R-sae2- in 4−6 form six- and five-membered chelate rings, respectively, which cause different steric strain and Jahn−Teller distortions at FeII centers. The sign of the D value was discussed by using angular overlap model (AOM) calculations for irons with different coordination geometry