Magnetic Behaviors of Heterospin Chains Consisting of Cobalt(II) Complexes and Dipyridylcarbenes

The 1:1 mixture of Co(Brhfpip)2 and D1py2 gave isomeric diazocobalt complexes, 1 and 2, formulated by [Co(Brhfpip)2(D1py2)]n. Complexes 1 and 2 have zigzag and linear chain structures by the cis and trans coordination of pyridine units in D1py2, respectively. After irradiation of microcrystalline samples, the generated carbene interacted with the cobalt ion to form ferromagnetic chains, 1c and 2c. Those isomeric chains exhibited slow magnetic relaxation with Ueff = 93 and 87 K and Hc = 20 and 13 kOe at 1.9 K for 1c and 2c, respectively

Magnetic Behaviors of Heterospin Chains Consisting of Cobalt(II) Complexes and Dipyridylcarbenes

The 1:1 mixture of Co(Brhfpip)2 and D1py2 gave isomeric diazocobalt complexes, 1 and 2, formulated by [Co(Brhfpip)2(D1py2)]n. Complexes 1 and 2 have zigzag and linear chain structures by the cis and trans coordination of pyridine units in D1py2, respectively. After irradiation of microcrystalline samples, the generated carbene interacted with the cobalt ion to form ferromagnetic chains, 1c and 2c. Those isomeric chains exhibited slow magnetic relaxation with Ueff = 93 and 87 K and Hc = 20 and 13 kOe at 1.9 K for 1c and 2c, respectively

Magnetic Properties after Irradiation of 1:4 Complexes Consisting of CoX₂, X = NCS^–, Cl^–, and NCO^–, and Phenylpyridyldiazomethane in Dilute Frozen Solutions: Axial Ligand Effect in Heterospin Single-Molecule Magnets

The solutions of 1:4 complexes of Co(X)2(D1py)4, X = Cl–, and NCO– and D1py = phenylpyridyldiazomethane, were photolyzed under cryogenic conditions, and their magnetic properties were investigated by direct current (DC) and alternating current (AC) magneto/susceptometries. After irradiation, the resulting cobalt-carbene complexes, Co(X)2(C1py)4, exhibited the behaviors of heterospin single-molecule magnets (SMMs) strongly depending on the axial ligands. In Co(X)2(C1py)4: X = Cl– and NCO–, the effective activation barriers, Ueff, for the reorientation of the magnetic moment and the resonant quantum tunneling time, τQ, characteristic to SMM properties were estimated to be 91 and 130 K, and 4 × 103 and 2 × 105 s, respectively. The τQ of Co(NCS)2(C1py)4 with Ueff = 89 K was found to be 6 × 102 s. In Co(X)2(C1py)4: X = Cl– and NCO–, temperature-dependent hysteresis loops were also observed below the blocking temperature (TB = 3.2 and 4.8 K, respectively) and the coercive forces, Hc, of 7.0 and 20 kOe at 1.9 K, respectively, were obtained. In a series of 1:4 complexes of Co(X)2(C1py)4, X = NCS–, Cl–, and NCO–, the axial ligands strongly affected the heterospin SMM properties, and the NCO– ion having the large magnitude of the ligand-field splitting in a spectrochemical series, gave the largest Ueff and Hc and the longest τQ

Magnetic Behaviors of Heterospin Chains Consisting of Cobalt(II) Complexes and Dipyridylcarbenes

The 1:1 mixture of Co(Brhfpip)2 and D1py2 gave isomeric diazocobalt complexes, 1 and 2, formulated by [Co(Brhfpip)2(D1py2)]n. Complexes 1 and 2 have zigzag and linear chain structures by the cis and trans coordination of pyridine units in D1py2, respectively. After irradiation of microcrystalline samples, the generated carbene interacted with the cobalt ion to form ferromagnetic chains, 1c and 2c. Those isomeric chains exhibited slow magnetic relaxation with Ueff = 93 and 87 K and Hc = 20 and 13 kOe at 1.9 K for 1c and 2c, respectively

Magnetic Properties after Irradiation of 1:4 Complexes Consisting of CoX₂, X = NCS^–, Cl^–, and NCO^–, and Phenylpyridyldiazomethane in Dilute Frozen Solutions: Axial Ligand Effect in Heterospin Single-Molecule Magnets

The solutions of 1:4 complexes of Co(X)2(D1py)4, X = Cl–, and NCO– and D1py = phenylpyridyldiazomethane, were photolyzed under cryogenic conditions, and their magnetic properties were investigated by direct current (DC) and alternating current (AC) magneto/susceptometries. After irradiation, the resulting cobalt-carbene complexes, Co(X)2(C1py)4, exhibited the behaviors of heterospin single-molecule magnets (SMMs) strongly depending on the axial ligands. In Co(X)2(C1py)4: X = Cl– and NCO–, the effective activation barriers, Ueff, for the reorientation of the magnetic moment and the resonant quantum tunneling time, τQ, characteristic to SMM properties were estimated to be 91 and 130 K, and 4 × 103 and 2 × 105 s, respectively. The τQ of Co(NCS)2(C1py)4 with Ueff = 89 K was found to be 6 × 102 s. In Co(X)2(C1py)4: X = Cl– and NCO–, temperature-dependent hysteresis loops were also observed below the blocking temperature (TB = 3.2 and 4.8 K, respectively) and the coercive forces, Hc, of 7.0 and 20 kOe at 1.9 K, respectively, were obtained. In a series of 1:4 complexes of Co(X)2(C1py)4, X = NCS–, Cl–, and NCO–, the axial ligands strongly affected the heterospin SMM properties, and the NCO– ion having the large magnitude of the ligand-field splitting in a spectrochemical series, gave the largest Ueff and Hc and the longest τQ

Molecular Structure and Magnetic Properties of 1-Ethyl-2-(1-oxy-3-oxo-4,4,5,5-tetramethylimidazolin-2-yl)-3-methylimidazolium Arylcarboxylates and Other Salts

1-Ethyl-2-(1-oxy-3-oxo-4,4,5,5-tetramethylimidazolin-2-yl)-3-methylimidazolium bromide, [EMINN]+[Br]−, carrying nitronylnitroxide (NN) in the cation unit, was prepared as a parent molecule and converted to seven salts, [EMINN]+[X]− (X = I, TFSI (bis(trifluoromethanesulfonyl)imide), BPh4 (tetraphenylborate), [EMINN]+1−3[BA1−3](1−3)−; BA1 (benzoic acid), BA2 (terephthalic acid), and BA3 (trimesic acid), and [EMINN]+[BANN]−; BANN (4-NN-benzoic acid)), by the ion-exchange reaction. The molecular structure of the cation units for all salts revealed by X-ray crystallography is similar, where the dihedral angles between the imidazolium ring and the NN planes are 51−58°. In the crystal structure, [EMINN]+[X]− (X = Br, I, TFSI, and BPh4) formed head-to-tail dimers, while the uniquely shaped dimers consisting of two [EMINN]+[carboxylate]− units were connected by the hydrogen bonding of water molecules to form a tape structure for [EMINN]+[BANN]− and 2D sheet structure for [EMINN]+2[BA2]2− and [EMINN]+3[BA3]3−. In the crystalline state, [EMINN]+[X]− showed behavior typical of a paramagnetic species with S = 1/2. The χmolT vs T plot for [EMINN]+[BANN]− was analyzed using a four-spin model to give J1/kB = −0.27 and J2/kB = −0.16 K. The plots for [EMINN]+2[BA2]2− and [EMINN]+3[BA3]3− were analyzed using an antiferromagnetic chain model to give J/kB = −62.1 and −86.5 K, respectively. In aqueous solution, on the other hand, the ESR spectra for all salts showed similar five-line signals due to the isolated NN moiety. The relaxivities (r1 and r2; 25 °C, 0.59 T, and 25 MHz) for [EMINN]+[Br]−, [EMINN]+[BA]−, [EMINN]+[BANN]−, [EMINN]+2[BA2]2−, and [EMINN]+3[BA3]3−, are r1 = 0.13, 0.14, 0.32, 0.26, and 0.40 and r2 = 0.17, 0.13, 0.31, 0.30, and 0.46 mM−1 s−1, respectively

Molecular Structure and Magnetic Properties of 1-Ethyl-2-(1-oxy-3-oxo-4,4,5,5-tetramethylimidazolin-2-yl)-3-methylimidazolium Arylcarboxylates and Other Salts

1-Ethyl-2-(1-oxy-3-oxo-4,4,5,5-tetramethylimidazolin-2-yl)-3-methylimidazolium bromide, [EMINN]+[Br]−, carrying nitronylnitroxide (NN) in the cation unit, was prepared as a parent molecule and converted to seven salts, [EMINN]+[X]− (X = I, TFSI (bis(trifluoromethanesulfonyl)imide), BPh4 (tetraphenylborate), [EMINN]+1−3[BA1−3](1−3)−; BA1 (benzoic acid), BA2 (terephthalic acid), and BA3 (trimesic acid), and [EMINN]+[BANN]−; BANN (4-NN-benzoic acid)), by the ion-exchange reaction. The molecular structure of the cation units for all salts revealed by X-ray crystallography is similar, where the dihedral angles between the imidazolium ring and the NN planes are 51−58°. In the crystal structure, [EMINN]+[X]− (X = Br, I, TFSI, and BPh4) formed head-to-tail dimers, while the uniquely shaped dimers consisting of two [EMINN]+[carboxylate]− units were connected by the hydrogen bonding of water molecules to form a tape structure for [EMINN]+[BANN]− and 2D sheet structure for [EMINN]+2[BA2]2− and [EMINN]+3[BA3]3−. In the crystalline state, [EMINN]+[X]− showed behavior typical of a paramagnetic species with S = 1/2. The χmolT vs T plot for [EMINN]+[BANN]− was analyzed using a four-spin model to give J1/kB = −0.27 and J2/kB = −0.16 K. The plots for [EMINN]+2[BA2]2− and [EMINN]+3[BA3]3− were analyzed using an antiferromagnetic chain model to give J/kB = −62.1 and −86.5 K, respectively. In aqueous solution, on the other hand, the ESR spectra for all salts showed similar five-line signals due to the isolated NN moiety. The relaxivities (r1 and r2; 25 °C, 0.59 T, and 25 MHz) for [EMINN]+[Br]−, [EMINN]+[BA]−, [EMINN]+[BANN]−, [EMINN]+2[BA2]2−, and [EMINN]+3[BA3]3−, are r1 = 0.13, 0.14, 0.32, 0.26, and 0.40 and r2 = 0.17, 0.13, 0.31, 0.30, and 0.46 mM−1 s−1, respectively

Molecular Structure and Magnetic Properties of 1-Ethyl-2-(1-oxy-3-oxo-4,4,5,5-tetramethylimidazolin-2-yl)-3-methylimidazolium Arylcarboxylates and Other Salts

1-Ethyl-2-(1-oxy-3-oxo-4,4,5,5-tetramethylimidazolin-2-yl)-3-methylimidazolium bromide, [EMINN]+[Br]−, carrying nitronylnitroxide (NN) in the cation unit, was prepared as a parent molecule and converted to seven salts, [EMINN]+[X]− (X = I, TFSI (bis(trifluoromethanesulfonyl)imide), BPh4 (tetraphenylborate), [EMINN]+1−3[BA1−3](1−3)−; BA1 (benzoic acid), BA2 (terephthalic acid), and BA3 (trimesic acid), and [EMINN]+[BANN]−; BANN (4-NN-benzoic acid)), by the ion-exchange reaction. The molecular structure of the cation units for all salts revealed by X-ray crystallography is similar, where the dihedral angles between the imidazolium ring and the NN planes are 51−58°. In the crystal structure, [EMINN]+[X]− (X = Br, I, TFSI, and BPh4) formed head-to-tail dimers, while the uniquely shaped dimers consisting of two [EMINN]+[carboxylate]− units were connected by the hydrogen bonding of water molecules to form a tape structure for [EMINN]+[BANN]− and 2D sheet structure for [EMINN]+2[BA2]2− and [EMINN]+3[BA3]3−. In the crystalline state, [EMINN]+[X]− showed behavior typical of a paramagnetic species with S = 1/2. The χmolT vs T plot for [EMINN]+[BANN]− was analyzed using a four-spin model to give J1/kB = −0.27 and J2/kB = −0.16 K. The plots for [EMINN]+2[BA2]2− and [EMINN]+3[BA3]3− were analyzed using an antiferromagnetic chain model to give J/kB = −62.1 and −86.5 K, respectively. In aqueous solution, on the other hand, the ESR spectra for all salts showed similar five-line signals due to the isolated NN moiety. The relaxivities (r1 and r2; 25 °C, 0.59 T, and 25 MHz) for [EMINN]+[Br]−, [EMINN]+[BA]−, [EMINN]+[BANN]−, [EMINN]+2[BA2]2−, and [EMINN]+3[BA3]3−, are r1 = 0.13, 0.14, 0.32, 0.26, and 0.40 and r2 = 0.17, 0.13, 0.31, 0.30, and 0.46 mM−1 s−1, respectively

Molecular Structure and Magnetic Properties of 1-Ethyl-2-(1-oxy-3-oxo-4,4,5,5-tetramethylimidazolin-2-yl)-3-methylimidazolium Arylcarboxylates and Other Salts

1-Ethyl-2-(1-oxy-3-oxo-4,4,5,5-tetramethylimidazolin-2-yl)-3-methylimidazolium bromide, [EMINN]+[Br]−, carrying nitronylnitroxide (NN) in the cation unit, was prepared as a parent molecule and converted to seven salts, [EMINN]+[X]− (X = I, TFSI (bis(trifluoromethanesulfonyl)imide), BPh4 (tetraphenylborate), [EMINN]+1−3[BA1−3](1−3)−; BA1 (benzoic acid), BA2 (terephthalic acid), and BA3 (trimesic acid), and [EMINN]+[BANN]−; BANN (4-NN-benzoic acid)), by the ion-exchange reaction. The molecular structure of the cation units for all salts revealed by X-ray crystallography is similar, where the dihedral angles between the imidazolium ring and the NN planes are 51−58°. In the crystal structure, [EMINN]+[X]− (X = Br, I, TFSI, and BPh4) formed head-to-tail dimers, while the uniquely shaped dimers consisting of two [EMINN]+[carboxylate]− units were connected by the hydrogen bonding of water molecules to form a tape structure for [EMINN]+[BANN]− and 2D sheet structure for [EMINN]+2[BA2]2− and [EMINN]+3[BA3]3−. In the crystalline state, [EMINN]+[X]− showed behavior typical of a paramagnetic species with S = 1/2. The χmolT vs T plot for [EMINN]+[BANN]− was analyzed using a four-spin model to give J1/kB = −0.27 and J2/kB = −0.16 K. The plots for [EMINN]+2[BA2]2− and [EMINN]+3[BA3]3− were analyzed using an antiferromagnetic chain model to give J/kB = −62.1 and −86.5 K, respectively. In aqueous solution, on the other hand, the ESR spectra for all salts showed similar five-line signals due to the isolated NN moiety. The relaxivities (r1 and r2; 25 °C, 0.59 T, and 25 MHz) for [EMINN]+[Br]−, [EMINN]+[BA]−, [EMINN]+[BANN]−, [EMINN]+2[BA2]2−, and [EMINN]+3[BA3]3−, are r1 = 0.13, 0.14, 0.32, 0.26, and 0.40 and r2 = 0.17, 0.13, 0.31, 0.30, and 0.46 mM−1 s−1, respectively

Crystal Structures and Magnetic Properties of Complexes of M^IICl₂ (M = Cu, Ni, and Co) Coordinated with 4-(<i>N</i>-<i>tert</i>-butyloxyamino)-2-(methoxymethylenyl)pyridine: 2D Magnetic Anisotropy of the Aminoxyl-Co^II Complex in the Crystalline State

Three metal complexes, [MIICl2(4NOPy-OMe)2] (M = Cu (1), Ni (2), and Co (3)), were prepared by mixing the corresponding metal chloride and 4-(N-tert-butyloxyamino)-2-(methoxymethylenyl)pyridine, 4NOPy-OMe, in 1:2 ratio. Complex 1 has two structures (complexes A and B) with similar coordination geometries, compressed octahedrons. In the crystal structure, complexes A and B locate alternately in short distances (Cradical··· Cβ = 3.17 and 3.23 Å) to form a 1-D chain structure. Complexes 2 and 3 are isomorphous and have a slightly distorted octahedral structure. In the crystal structure, both complexes have intermolecular short contacts (Cradical···Cα = 3.46 and 3.52 Å for 2 and 3, respectively) to form the 2-D structures. The temperature dependence of the χmolT values for the three complexes indicated that the magnetic interactions between the radicals and the metal ions within the complexes were ferromagnetic. By fitting a modified Fisher 1-D model to the data of the χmolT vs T plot for 1, we estimated the intra- and intermolecular (intrachain) exchange coupling constants to be J1/kB = 60.2 and J2/kB = −7.02 K, respectively. On the other hand, complexes 2 and 3 showed steep increases of the χmolT value below ca. 3 K, indicating that the long-range magnetic ordering is operating. The 1/χmol vs T plot for 2 was analyzed by a Curie−Weiss model to give θ = 6.25 K and C = 2.02 cm3 K mol-1 with gNi = 2.25. Complex 3 was investigated in more detail using an orientated sample. Magnetic behavior strongly depends on the direction of the applied field, in which the c* axis perpendicular to the ab plane is an easy axis for magnetization. Direct current (dc) and alternating current (ac) magnetic susceptibility measurements revealed that complex 3 had a magnetic phase transition of Tc = 2.14 K and exhibited a glasslike magnetic behavior below Tc