Relationship between Torsion and Anisotropic Exchange Coupling in a Tb(III)-Radical-Based Single-Molecule Magnet.

The incorporation of paramagnetic ligands within rare-earth ion clusters exhibiting large magnetic anisotropy has provided significant advancement in the design of single-molecule magnets (SMMs) with large blocking temperatures. However, the exchange interaction in such systems is complex and difficult to probe by conventional magnetometry techniques, and little is known about the structural relationships. Inelastic neutron scattering and terahertz electron paramagnetic resonance measurements are used complimentarily to investigate the large exchange interaction between a rare earth-radical pair in a Tb(III)-based SMM complex. The origin of the exchange interaction is investigated for two molecular species in the crystallographic unit cell that exhibit different bonding structures between Tb(III) and a 2pyNO radical. A correlation between the Tb-O-N-C torsion angles and the magnitudes of exchange couplings is found. Interestingly, a large nondegeneracy within the ground-state doublet is present for the larger torsion angle species. It is essential to consider the balance of two channels of exchange coupling, 2p-4f hybridization and 2p-5d charge transfer, to explain this characteristic behavior. The former channel gives the antiferromagnetic interaction, and the latter gives the ferromagnetic one. When an effective J = (1)/2 Ising-type Hamiltonian is applied, the exchange couplings are evaluated to be antiferromagnetic J(z) = 9.89 meV (79.8 cm(-1)) for the low torsion angle (3.8°) species and J(z) = 7.39 meV (59.6 cm(-1)) for the larger torsion angle (15.8°) species. It is also found that a small percentage of the transverse exchange component must be included for the larger torsion angle to account for the observed nondegenerate ground state. The symmetry of the exchange couplings is discussed by considering the characters of d and f orbitals.

Freezing effect on brain density in postmortem CT.

Two 60-year-old males were found at their homes whose bodies had deteriorated due to putrefaction. To prevent worm invasion and minimize deterioration, dry ice was used prior to the autopsy investigation. Prior to autopsy, postmortem CT demonstrated a decreased density in brain parenchyma at the dry-iced side, and autopsy revealed deteriorated brain parenchyma with frozen effect (presented like sherbet). Moreover, the deteriorated cerebral parenchyma maintained their structure and they were evaluated by cutting. When lower CT density presents in postmortem CT, the freezing effect may need to be considered and the physician should evaluate the cadaver's postmortem condition to prevent misdiagnoses.

Doubly TEMPO-coordinated gadolinium(III), lanthanum(III), and yttrium(III) complexes. Strong superexchange coupling across rare earth ions.

We prepared crystalline [RE(III)(hfac)3(TEMPO)2] (RE = Gd, La, Y), where TEMPO and hfac stand for 2,2,6,6-tetramethylpiperidin-1-oxyl and 1,1,1,5,5,5-hexafluoropentane-2,4-dionate, respectively. The X-ray crystal structure of TEMPO-coordinated RE compounds was determined for the first time. The Gd and Y analogues are isomorphous, and the La derivative has a similar molecular skeleton. The Gd-O(TEMPO) bond lengths were 2.322(3) and 2.354(3) Å with the O-Gd-O angle of 140.36(11)°. The magnetic study clarified that [Gd(hfac)3(TEMPO)2] behaved as a ground Stotal = 7/2 species. The La and Y analogues showed the superexchange interactions across the diamagnetic ions with 2JTEMPO1-TEMPO2/kB = -14.9(1) and -49.8(2) K, respectively. Assuming the presence of a similar interaction like the Y derivative, the Gd-TEMPO exchange couplings are estimated with 2JGd-TEMPO/kB = -12.9(5) and +8.0(6) K.

Single-molecule magnet [Tb(hfac)3(2pyNO)] (2pyNO = t-butyl 2-pyridyl nitroxide) with a relatively high barrier of magnetization reversal.

The crystallographic analysis of the title compound shows that there are two crystallographically independent molecules in a unit cell. The magnetic study clarified that every molecule behaved as a single-molecule magnet. Two series of the out-of-phase ac susceptibility signals appeared around 10 K even at zero dc field. The activation energies (Δ) for the magnetization reversal were estimated as Δ((1))/k(B) = 39.2(3) K with τ0((1)) = 4.2(4) × 10(-8) s and Δ((2))/k(B) = 36(2) K with τ0((2)) = 4.1(12) × 10(-7) s, where τ0 stands for the pre-exponential factor in the Arrhenius analysis. Magnetic hysteresis was recorded at 1.6 K by means of a pulsed-field technique. The role of exchange coupling is discussed.