Pyrimideine-Bridged Cobalt(II) Complexes with a Chiral 3-D Network Showing Weak Ferromagnetism

Nakayama, Kensuke; Ishida, Takayuki; Takayama, Ryo; Hashizume, Daisuke; Yasui, Masanori; Iwasaki, Fujiko; Nogami, Takashi

doi:10.1246/cl.1998.497

Cited by 47 publications

(20 citation statements)

References 18 publications

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“…Fitting the magnetic data to the Curie-Weiss law (c m C/ (T À q)) gives a Weiss constant of q 2.44 K with a Curie constant of C 2.74 cm 3 K mol À1 (g 2.41) for 1 a in the temperature range of 6 ± 35 K, and q 11.1 K with C 1.24 cm 3 K mol À1 (g 2.23) for 2 a in the temperature range of 30 ± 300 K. [24] The positive Weiss constants indicate that there are ferromagnetic interactions between M II magnetic centers bridged by azide ligand with end-to-end coordination. The magnitude of the Weiss constant of 2 a is stronger than that of 1 a.…”

Section: Magnetic Properties Of Hydrated Species 1 a And 2 Amentioning

confidence: 96%

Unusual Ferromagnetic Couplings in Single End-to-End Azide-Bridged Cobalt(II) and Nickel(II) Chain Systems

et al. 2001

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Two new one-dimensional single azide-bridged metal(II) compounds [[M(5-methylpyrazole)4(N3)]n](ClO4)n(H2O)n [M = Co (1a), Ni (2a)] were prepared by treating an M(II) ion with stoichiometric amount of sodium azide in the presence of four equivalents of the 3(5)-methylpyrazole ligand. The isostructural compounds 1a and 2a crystallize in the monoclinic space group P2(1)/n. The azide bridging ligands have a unique end-to-end coordination mode that brings two neighboring metal centers into a cis-position with respect to the azide unit to form single end-to-end azide-bridged cobalt(II) and nickel(II) chains. The two neighboring metal atoms at inversion centers adopt octahedral environments with four equatorial 3(5)-methylpyrazole ligands and two axial azide bridges. Two adjacent equatorial least-squares planes form dihedral angles of 60.5 degrees and 60.6 degrees for Co and Ni, respectively. In addition, the metal-azide-metal units form large M-N3-M torsion angles, which are magnetically important geometrical parameters, of 71.6 degrees for M=Co and 75.7 degrees for M=Ni. It should also be noted that the M-N-N angles associated with end-to-end azide group, another magnetically important structural parameter, fall into the experimentally observed range of 120-140 degrees as 128.3(3) and 147.8(3) degrees for cobalt species and 128.4(2) and 146.1(3) degrees for nickel species; these values deviate from the theoretical value of around 164 degrees at which the incidental orthogonality is achieved under the torsion angle of 0 degrees. The compounds 1a and 2a have unique magnetic properties of ferromagnetism, zero-field splitting, and spin canting. The MO calculations indicate that the quasiorthogonality between the magnetic orbitals of metal ions and the p atomic orbitals of the bridging azide is possible in the observed structures and leads to the ferromagnetism. The spin canting related to the perturbation of ferromagnetism arises from the magnetic anisotropy and antisymmetric interactions judged by the structural parameters of the zero-field splitting and the tilted MN4 planes in a chain. The enhancement of magnetic interactions was accomplished by dehydrating the chain compounds to afford two soft magnets with critical temperature T(C) and coercive field of 2 K and 35 G for 1b and 2.3 K and 20 G for 2b, respectively.

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Section: Magnetic Properties Of Hydrated Species 1 a And 2 Amentioning

confidence: 96%

Unusual Ferromagnetic Couplings in Single End-to-End Azide-Bridged Cobalt(II) and Nickel(II) Chain Systems

et al. 2001

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“…Some complexes containing this ligand indeed exhibit ferromagnetic interactions [30][31][32][33] whereas others show antiferromagnetic interactions. [34][35][36][37][38][39][40] The same holds true for the C 3symmetric m 3 -bridging ligand 1,3,5-triazine, which may be regarded as the triangular extension of the m 2 -bridging ligand pyrimidine, where both ferromagnetically and antiferromagnetically coupled trinuclear Ti III complexes have been reported. [41,42] Ferromagnetic interactions were also achieved with a modified resorcinol ligand bridging two Fe III centers in a m-phenylene arrangement.…”

Section: Introductionmentioning

confidence: 93%

Trinuclear Copper Complexes with Triplesalen Ligands: Geometric and Electronic Effects on Ferromagnetic Coupling via the Spin‐Polarization Mechanism

Glaser

Heidemeier

Strautmann

et al. 2007

Chemistry A European J

145

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A series of trinuclear Cu(II) complexes with the tris(tetradentate) triplesalen ligands H(6)talen, H(6)talen(tBu(2) ), and H(6)talen(NO(2) ), namely [(talen)Cu(II) (3)] (1), [(talen(tBu(2) ))Cu(II) (3)] (2), and [(talen(NO(2) ))Cu(II) (3)] (3), were synthesized and their molecular and electronic structures determined. These triplesalen ligands provide three salen-like coordination environments bridged in a meta-phenylene arrangement by a phloroglucinol backbone. The structure of [(talen)Cu(II) (3)] (1) was communicated recently. The structure of the tert-butyl derivative [(talen(tBu(2) ))Cu(II) (3)] (2) was established in three different solvates. The molecular structures of these trinuclear complexes show notable differences, the most important of which is the degree of ligand folding around the central Cu(II)-phenolate bonds. This folding is symmetric with regard to the central phloroglucinol backbone in two structures, where it gives rise to bowl-shaped overall geometries. For one solvate two trinuclear triplesalen complexes form a supramolecular disk-like arrangement, hosting two dichloromethane molecules like two pearls in an oyster. The FTIR spectra of these complexes indicate the higher effective nuclear charge of Cu(II) in comparison to the trinuclear Ni(II) complexes by the lower C--O and higher C=N stretching frequencies. The UV/Vis/NIR spectra of 1-3 reflect the stronger ligand folding in the tert-butyl complex 2 by an intense phenolate-to-Cu(II) LMCT. This absorption is absent in 1 and is obscured by the nitro chromophore in 3. The more planar molecular structures cause orthogonality of the Cu(II) d(x(2)-y(2) ) orbital and the phenolate O p(z) orbital, which leads to small LMCT dipole strengths. Whereas 1 and 3 exhibit only irreversible oxidations, 2 exhibits a reversible one-electron oxidation at +0.26 V, a reversible two-electron oxidation at +0.59 V, and a reversible one-electron oxidation at +0.81 V versus Fc(+)/Fc. The one-electron oxidized form 2(+) is strongly stabilized with respect to reference mononuclear salen-like Cu complexes. Chemical one-electron oxidation of 2 to 2(+) allows the determination of its UV/Vis/NIR spectrum, which indicates a ligand-centered oxidation that can be assigned to the central phloroglucinol unit by analogy with the trinuclear Ni triplesalen series. Delocalization of this oxidation over three Cu(II)-phenolate subunits causes the observed energetic stabilization of 2(+). Temperature-dependent magnetic susceptibility measurements reveal ferromagnetic couplings for all three trinuclear Cu(II) triplesalen complexes. The trend of the coupling constants can be rationalized by two opposing effects: 1) electron-withdrawing terminal substituents stabilize the central Cu(II)-phenolate bond, which results in a stronger coupling, and 2) ligand folding around the central Cu(II)-phenolate bond opens a bonding pathway between the magnetic Cu(II) d(x(2)-y(2) ) orbital and the phenolate O p(z) orbital, which results in a stronger coupling. Density functional calculations indicate ...

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“…22 Consequently, the bridging ligands are extended to a three-atom-singlebridge mode, 12,23 including μ-1,3-N 3 − (azide), 7,24,25 μ-1,3-NCNCN − (dicyanoamide), [26][27][28][29][30] or μ-OC(R)O (carboxylate acid). [31][32][33] The -NCNin μ-imidazolate [34][35][36] and μ-pyrimidine [37][38][39][40][41][42][43][44] can be regarded as quasi-three-atom bridges. Among them, pyrimidine is a typical neutral bridge (-NCN-) in constructing coordination polymers in 2D-3D networks, such as [Co(pyrimidine) 2 (NCS) 2 ], 37 [Co(pyrimidine) 2 X 2 ] (X = Cl − , Br − , N 3 − ), 38,39 [Cu(pyrimidine)(ClO 4 ) 2 ] 40 and [Fe(pyrimidine) 2 Cl 2 ].…”

Section: Introductionmentioning

confidence: 99%

Weak ferromagnetism in chiral diamond-like neutral networks: Mn(2-pymS)2 and Co(2-pymS)2 (2-pymSH = 2-mercaptopyrimidine)

et al. 2012

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The reactions of 2-mercatopyrimidine with MCl(2) (M = Mn(2+) or Co(2+)) in solvothermal conditions result single crystals of Mn(2-pymS)(2)1 and Co(2-pymS)(2)2. The two complexes both have the diamond-like topology frameworks, which could be traced back to the similar way of pyrimidine rings acting as the asymmetric bridging ligands. Interestingly, although they have similar chemical formulas, structural analysis by single-crystal X-ray diffraction studies reveals that the sulfur atoms play different roles in 1 and 2. For 1, the Mn ion lies in a distorted octahedral environment bonded to four nitrogen atoms and two sulfur atoms, whereas the Co ion in a distorted tetrahedral environment only coordinates to nitrogen atoms of pyrimidine ligands in the case of Co(2-pymS)(2)2. More interestingly, although magnetic measurements for both complex 1 and 2 indicate long range magnetic ordering and spin canting below the critical temperature (20 K for 1 and 42.9 K for 2), a hysteresis loop can be observed even at 40 K, which is just below the T(C) for complex 2, which is distinctly harder than 1.

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Pyrimideine-Bridged Cobalt(II) Complexes with a Chiral 3-D Network Showing Weak Ferromagnetism

Abstract: The reaction of CoX2(X=Br, Cl) and pyrimidine (PM) in H2O gave crystals of CoPM2X2. The crystal structure analysis revealed a chiral three-dimensional network of the Co(II) ions. Weak ferromagnetism with relatively large spontaneous magnetization was observed below 5 K for both compounds.

Cited by 47 publications

References 18 publications

Unusual Ferromagnetic Couplings in Single End-to-End Azide-Bridged Cobalt(II) and Nickel(II) Chain Systems

Unusual Ferromagnetic Couplings in Single End-to-End Azide-Bridged Cobalt(II) and Nickel(II) Chain Systems

Trinuclear Copper Complexes with Triplesalen Ligands: Geometric and Electronic Effects on Ferromagnetic Coupling via the Spin‐Polarization Mechanism

Weak ferromagnetism in chiral diamond-like neutral networks: Mn(2-pymS)2 and Co(2-pymS)2 (2-pymSH = 2-mercaptopyrimidine)

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