ABSTRACT
A squarate (sq) bridge was applied to heavy lanthanide (Ln) complexes for possible development of high-performance single-ion magnets (SIMs). A selective synthetic method for lanthanide squarate hydrates [Ln2(sq)3(H2O)8]n (abbreviated as Ln-sq) has been established, where Ln stands for Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. As the crystallographic analysis clarified, they all form a bilayer polymeric structure, which is isomorphic to known Eu-sq and Tb-sq. The coordination structures are described as an almost ideal square antiprism with D4d symmetry. Frequency-dependent susceptibility was recorded in alternating-current magnetic measurements for Ln = Tb, Dy, Er, Tm, and Yb. In particular, as for less studied Ln-based SIMs, the effective magnetization-reversal barriers, Ueff/kB = 21.4 ± 0.4 K (in a bias field of 1800 Oe) and 57.0 ± 0.4 K (400 Oe), were characterized for Tm-sq and Yb-sq, respectively, according to the Orbach-type relaxation mechanism plus a direct or the Raman mechanism. The barrier found for Yb-sq is the highest among those for all the compounds investigated here, and also regarded as one of the largest values for the Yb-based SIMs known so far. The complete-active-space self-consistent-field (CASSCF) calculation was applied to Tm- and Yb-sq. The ground doublet states with mJ = ±6 for the Tm3+ ion and mJ = ±7/2 for the Yb3+ ion were reproduced.
ABSTRACT
Recently, mixed-metal metal-organic frameworks (MOFs) have been attracting much attention in various fields. In this study, we have systematically investigated the magnetic properties of CoxNi1-x-MOF-74 [Co2xNi2(1-x)(dhtp), where H4dhtp = 2,5-dihydroxyterephthalic acid] with two different kinds of metals (Co and Ni) across the composition range 0 ≤ x ≤ 1. Bimetallic CoxNi1-x-MOF-74 (x = 0.752, 0.458, and 0.233) were successfully synthesized and confirmed to have homogeneous metal distributions. Weak ferromagnetic (canted antiferromagnetic) behavior was exhibited, while homometallic Co-MOF-74 and Ni-MOF-74 are antiferromagnetic. We also investigated the effects of C2H4 sorption on the magnetic properties and found that C2H4-adsorbed Co0.5Ni0.5-MOF-74 exhibited a change in the interchain magnetic interaction.
ABSTRACT
The effect of hydrogen bonds around the active site of Anabaena [2Fe-2S] ferredoxin (Fd) on a vertical ionization potential of the reduced state (IP(red)) is examined based on the density functional theory (DFT) calculations. The results indicate that a single hydrogen bond increases the relative stability of the reduced state, and shifts IP(red) to a reductive side by 0.31-0.33 eV, regardless of the attached sulfur atoms. In addition, the IP(red) value can be changed by the number of hydrogen bonds around the active site. The results also suggest that the redox potential of [2Fe-2S] Fd is controlled by the number of hydrogen bonds because IP(red) is considered to be a major factor in the redox potential. Furthermore, there is a possibility that the redox potentials of artificial iron-sulfur clusters can be finely controlled by the number of the hydrogen bonds attached to the sulfur atoms of the cluster.
