title: Carbonato-bridged Ni(II)2Ln(III)2 (Ln(III) = Gd(III), Tb(III), Dy(III)) complexes generated by atmospheric CO2 fixation and their single-molecule-magnet behavior: [(μ4-CO3)2{Ni(II)(3-MeOsaltn)(MeOH or H2O)Ln(III)(NO3)}2]·solvent [3-MeOsaltn = N,N'-bis(3-methoxy-2-oxybenzylidene)-1,3-propanediaminato].
abstract: Atmospheric CO2 fixation of [Ni(II)(3-MeOsaltn)(H2O)2]·2.5H2O [3-MeOsaltn = N,N'-bis(3-methoxy-2-oxybenzylidene)-1,3-propanediaminato], Ln(III)(NO3)3·6H2O, and triethylamine occurred in methanol/acetone, giving a first series of carbonato-bridged Ni(II)2Ln(III)2 complexes [(μ4-CO3)2{Ni(II)(3-MeOsaltn)(MeOH)Ln(III)(NO3)}2] (1Gd, 1Tb, and 1Dy). When the reaction was carried out in acetonitrile/water, it gave a second series of complexes [(μ4-CO3)2{Ni(II)(3-MeOsaltn)(H2O)Ln(III)(NO3)}2]·2CH3CN·2H2O (2Gd, 2Tb, and 2Dy). For both series, each Ni(II)2Ln(III)2 structure can be described as two di-μ-phenoxo-bridged Ni(II)Ln(III) binuclear units bridged by two carbonato CO3(2-) units to form a carbonato-bridged (μ4-CO3)2{Ni(II)2Ln(III)2} structure. The high-spin Ni(II) ion has octahedral coordination geometry, and the Ln(III) ion is coordinated by O9 donor atoms from Ni(II)(3-MeOsaltn), bidentate NO3(-), and one and two oxygen atoms of two CO3(2-) ions. The NO3(-) ion for the first series roughly lie on Ln-O(methoxy) bonds and are tilted toward the outside, while for the second series, the two oxygen atoms roughly lie on one of the Ln-O(phenoxy) bonds due to the intramolecular hydrogen bond. The temperature-dependent magnetic susceptibilities indicated a ferromagnetic interaction between the Ni(II) and Ln(III) ions (Ln(III) = Gd(III), Tb(III), Dy(III)) for all of the complexes, with a distinctly different magnetic behavior between the two series in the lowest-temperature region due to the Ln(III)-Ln(III) magnetic interaction and/or different magnetic anisotropies of the Tb(III) or Dy(III) ion. Alternating-current susceptibility measurements under the 0 and 1000 Oe direct-current (dc) bias fields showed no magnetic relaxation for the Ni(II)2Gd(III)2 complexes but exhibited an out-of-phase signal for Ni(II)2Tb(III)2 and Ni(II)2Dy(III)2, indicative of slow relaxation of magnetization. The energy barriers, Δ/kB, for the spin flipping were estimated from the Arrhenius plot to be 12.2(7) and 6.1(3) K for 1Tb and 2Tb, respectively, and 18.1(6) and 14.5(4) K for 1Dy and 2Dy, respectively, under a dc bias field of 1000 Oe. Compound 1Dy showed relatively slow relaxation of magnetization reorientation even at zero dc applied field with Δ/kB = 6.6(4) K.
authors.affiliation: Department of Chemistry, Faculty of Science, Kumamoto University, Kumamoto 860-8555, Japan.
authors.forename: Soichiro
authors.initials: S
authors.lastname: Sakamoto
authors.forename: Takeshi
authors.initials: T
authors.lastname: Fujinami
authors.forename: Koshiro
authors.initials: K
authors.lastname: Nishi
authors.forename: Naohide
authors.initials: N
authors.lastname: Matsumoto
authors.forename: Naotaka
authors.initials: N
authors.lastname: Mochida
authors.forename: Takayuki
authors.initials: T
authors.lastname: Ishida
authors.forename: Yukinari
authors.initials: Y
authors.lastname: Sunatsuki
authors.forename: Nazzareno
authors.initials: N
authors.lastname: Re
mesh_terms: D001597:Benzylidene Compounds / Q000737:chemistry; D002245:Carbon Dioxide / Q000737:chemistry*; D056831:Coordination Complexes / Q000737:chemistry; D005682:Gadolinium / Q000737:chemistry*; D028581:Lanthanoid Series Elements / Q000737:chemistry*; D008280:Magnetics; D000432:Methanol / Q000737:chemistry; D008958:Models, Molecular; D009532:Nickel / Q000737:chemistry*; D011407:Propane / Q000737:chemistry; D012997:Solvents; D014867:Water / Q000737:chemistry
chemical_list: D001597:Benzylidene Compounds; D056831:Coordination Complexes; D028581:Lanthanoid Series Elements; D012997:Solvents; D014867:Water; D002245:Carbon Dioxide; D009532:Nickel; D005682:Gadolinium; D011407:Propane; D000432:Methanol