Structural design of easy-axis magnetic anisotropy and determination of anisotropic parameters of Ln(III)-Cu(II) single-molecule magnets

Four dinuclear Ln^III? Cu^II complexes with Ln=Tb ( 1 ), Dy ( 2 ), Ho ( 3 ), and Er ( 4 ) were synthesized to investigate the relationship between their respective magnetic anisotropies and ligand‐field geometries. These complexes were crystallographically isostructural, and a uni‐axial ligand field was achieved by using three phenoxo oxygen groups. Complexes 1 and 2 displayed typical single‐molecule magnet (SMM) behaviors, of which the out‐of‐phase susceptibilities were observed in the temperature range of 1.8–5.0 K ( 1 ) and 1.8–20.0 K ( 2 ). The Cole–Cole plots exhibited a semicircular shape with α parameters in the range of 0.08–0.18 (2.6–4.0 K) and 0.07–0.24 (3.5–7.0 K). The energy barriers Δ/k_B were estimated from the Arrhenius plots to be 32.9(4) K for 1 and 26.0(5) K for 2 . Complex 3 displayed a slow magnetic relaxation below 3.0 K, whereas complex 4 did not show any frequency‐dependent behavior for both in‐phase and out‐of‐phase susceptibilities, which indicates that easy‐axis anisotropy was absent. The temperature dependence of the dc susceptibilities for the field‐aligned samples of 1 – 3 revealed that the χ_MT value continuously increased as the temperature was lowered, which indicates the presence of low‐lying Stark sublevels with the highest |J_z| values. In contrast, complex 4 displayed a smaller and temperature‐independent χ_MT value, which also indicates that easy‐axis anisotropy was absent. Simultaneous analyses were carried out for 1 – 3 to determine the magnetic anisotropy parameters on the basis of the Hamiltonian that considers B₂⁰, B₄⁰, and B₆⁰.     

Living ethylene/norbornene copolymerisation catalyzed by titanium complexes having two pyrrolide-imine chelate ligands

Ethylene/norbornene copolymerisation behaviour of titanium complexes with two pyrrolide-imine chelate ligands is described.     

Studies on the Magnetic Ground State of a Spin Möbius Strip

Here we report the synthesis, structure and detailed characterisation of three n‐membered oxovanadium rings, Na_n[(V=O)_nNa_n(H₂O)_n(α, β, or γ‐CD)₂]?m H₂O (n=6, 7, or 8), prepared by the reactions of (V=O)SO₄?x H₂O with α, β, or γ‐cyclodextrins (CDs) and NaOH in water. Their alternating heterometallic vanadium/sodium cyclic core structures were sandwiched between two CD moieties such that O‐Na‐O groups separated the neighbouring vanadyl ions. Antiferromagnetic interactions between the S=1/2 vanadyl ions led to S=0 ground states for the even‐membered rings, but to two quasi‐degenerate S=1/2 states for the spin‐frustrated heptanuclear cluster.     

Density functional study on geometrical features and electronic structures of di-mu-oxo-bridged [Mn2O2(H2O)8]q+ with Mn(II), Mn(III), and Mn(IV)

We report the geometrical features and electronic structures of di-mu-oxo-bridged Mn-Mn binuclear complexes with H2O ligands [Mn2O2(H2O)8]q+ in the iso- and mixed-valence oxidation states. All of the combinations among Mn(II), Mn(III), and Mn(IV) ions are considered the oxidation states of the Mn-Mn center, and the changes in molecular structure induced by the different electron configurations of Mn-based orbitals are investigated in relation to the oxygen-evolving complex (OEC) of photosystem II. The stable geometries of complexes are determined by using the hybrid-type density functional theory for both of the highest- and lowest-spin couplings between Mn sites, and the lowest-spin-coupled states are energetically more favorable than the highest-spin-coupled states except in the case of the complexes with the Mn(II) ion. The coordination positions of H2O ligands at the Mn(II) site tend to shift from the octahedral positions in contrast to those at the Mn(III) and Mn(IV) sites. The shape of the Mn2O2 core and the distances between the Mn ions and the H2O ligands vary depending on the electron occupations of the octahedral eg orbitals on the Mn site with an antibonding nature for the Mn-ligand interactions, indicating the trend as Mn(II)-O > Mn(III)-O and Mn(IV)-O, O-Mn(II)-O > O-Mn(III)-O > O-Mn(IV)-O among the iso-valence Mn2O2 cores, and O-Mn(lower)-O < O-Mn(higher)-O within the mixed-valence Mn2O2 core, and as Mn(II)-OH2 and Mn(III)-OH2 > Mn(IV)-OH2 for the axial H2O ligand. The optimized geometries of model complexes are compared with the X-ray structure of the OEC, and it is suggested that the cubane-like Mn cluster of the active site may not contain a Mn(II) ion. The effective exchange integrals are estimated by applying the approximate spin projection to clarify the magnetic coupling between Mn sites, and the superexchange pathways through the di-mu-oxo bridge are examined on the basis of the singly occupied magnetic orbitals derived from the singlet-coupled natural orbitals in the broken-symmetry state. The comparisons of the calculated results between [Mn2O2(H2O)8]q+ in this study and [Mn2O2(NH3)8]q+ reported by McGrady et al. suggest that the symmetric pathways are dominant to the exchange coupling constant, and the crossed pathway would be less important for the former than it would for the latter in the Mn(III)-Mn(III), Mn(IV)-Mn(IV), and Mn(III)-Mn(IV) oxidation states.     

A clue to elusive macrocycles: unusually facile, spontaneous polymerization of a hexagonal diethynylbenzene macrocycle

[structures: see text] A hexagonal diethynylbenzene macrocycle having exterior octyloxymethyl groups undergoes spontaneous polymerization at room temperature to form hardly soluble materials, in contrast to the corresponding dehydrotetramer and dehydrooctamer, which are stable enough to show their melting points at higher than 140 degrees C.     

X-ray magnetic circular dichroism of size-selected, thiolated gold clusters

We report herein the X-ray magnetic circular dichroism (XMCD) at the Au L2,3 edges of a series of Au clusters protected by glutathione (GSH). The samples used here included AuN(SG)M with (N, M) = (10, 10), (15, 13), (18, 14), (22, 16), (25, 18), (29, 20), (39, 24) and a sodium gold(I) thiomalate (SGT) as a reference. Magnetic moments per cluster were found to be increased with size, whereas those per Au-S bond were nearly constant. This finding suggests that a localized hole created by Au-S bonding at the gold/glutathione interface, rather than the quantum size effect, is responsible for the spin polarization of gold clusters.     

A new hexaferrocene complex with a [M3(mu3-O)]7+ core

The new hexaferrocene complex 1 has been synthesized and characterized by X-ray diffraction. Its magnetization data were fitted to a detailed theoretical model that considers nonequivalent exchange parameters between Fe ions to yield the magnetic exchange coupling values of J1/kB = -31.5 K and J2/kB = -25.8 K. Moreover, the cyclic voltammogram of complex 1 confirmed its redox activity associated with the presence of ferrocene units, with very small or negligible electronic interactions between them.     

Novel synthesis of bridged phenylthienylethenes and dithienylethenes via Pd-catalyzed double-cyclization reactions of diarylhexadienynes

[reaction: see text] Bridged phenylthienylethenes and dithienylethenes were synthesized via Pd-catalyzed double-cyclization reactions of (Z,Z)-1,6-diaryl-1,5-hexadien-3-ynes. Pd-catalyzed as well as photoinduced Z/E isomerization of the products were also investigated.     

Kelvin-wave cascade on a vortex in superfluid 4He at a very low temperature

A study by computer simulation is reported of the behavior of a quantized vortex line at a very low temperature when there is continuous excitation of low-frequency Kelvin waves. There is no dissipation except by phonon radiation at a very high frequency. It is shown that nonlinear coupling leads to a net flow of energy to higher wave numbers and to the development of a simple spectrum of Kelvin waves that is insensitive to the strength and frequency of the exciting drive. The results are likely to be relevant to the decay of turbulence in superfluid 4He at very low temperatures.     

Success or Failure of Chiral Crystallization of Similar Heterocyclic Compounds

Single crystals of two achiral and planar heterocyclic compounds, C₉H₈H₃O(CA1) and C₈H₅NO₂ (CA4), recrystallized from ethanol, were characterized by single crystal X-ray analysis, respectively, and chiral crystallization was observed only for CA1 as P2₁2₁2₁ (# 19), whereas it was not observed for CA4 P2₁/c (# 14). In CA1, as a monohydrate, the hydrogen bonds were pronounced around the water of crystallization (O4), and the planar cyclic sites were arranged in parallel to slightly tilted positions. On the other hand, an anhydride CA4 formed a dimer by hydrogen bonds between adjacent molecules in the crystal, which were aggregated by van der Waals forces and placed in parallel planar cyclic sites.