Search Results (4)

Two ferrocenecarboxylate (fca)-bridged dirhodium (Rh₂) complexes, [Rh₂(fca)₄] (1) and [Rh₂(fca)(piv)₃] (2; piv = pivalate), were prepared through the carboxylate-exchange reactions of [Rh₂(O₂CCH₃)₄(H₂O)₂] and [Rh₂(piv)₄], respectively, with fcaH and characterized by ¹H NMR, ESI-TOF-MS, and elemental analyses. Single-crystal X-ray diffraction analyses of [Rh₂(fca)₄(MeOH)₂] (1(MeOH)₂) and [Rh₂(fca)(piv)₃(MeOH)₂] (2(MeOH)₂), which are recrystallized from MeOH-containing solutions of 1 and 2, revealed that (1) 1(MeOH)₂ and 2(MeOH)₂ possess homoleptic and heteroleptic paddlewheel-type dinuclear structures, respectively; (2) both complexes have a single Rh–Rh bond (2.3771(3) Å for 1(MeOH)₂, 2.3712(3) Å for 2(MeOH)₂); and (3) the cyclopentadienyl rings of the fca ligands in 1(MeOH)₂ adopt an eclipsed conformation, whereas those in 2(MeOH)₂ are approximately 12–14° rotated from the staggered conformation. Density functional theory (DFT) calculations revealed that (1) the electronic configurations of the Rh₂ core in 1(MeOH)₂ and 2(MeOH)₂ are π⁴σ²δ²π*²δ*²π*² and π⁴σ²δ²δ*²π*⁴, respectively; and (2) the occupied molecular orbitals (MOs) localized on the fca ligands are energetically degenerate and relatively more unstable than those on the Rh₂ cores. Absorption features and electrochemical properties of 1 and 2 were investigated in a 9:1 CHCl₃-MeOH solution and compared with those of fcaH and [Rh₂(piv)₄]. Through examining the obtained results in detail using time-dependent DFT (TDDFT) and unrestricted DFT, we found that 1 and 2 exhibit charge transfer excitations between the fca ligands and Rh₂ cores, and 1 shows electronic interactions between ferrocene units through the Rh₂ core in the electrochemical oxidation process. Full article

The electronic, optical, and magnetic properties of Nd-doped ZnO systems were calculated using the DFT/GGA + U method. According to the results, the Nd dopant causes lattice parameter expansion, negative formation energy, and bandgap narrowing, resulting in the formation of an N-type degenerate semiconductor. Overlapping of the generated impurity and Fermi levels results in a significant trap effect that prevents electron-hole recombination. The absorption spectrum demonstrates a redshift in the visible region, and the intensity increased, leading to enhanced photocatalytic performance. The Nd-doped ZnO system displays ferromagnetic, with FM coupling due to strong spd-f hybridization through magnetic exchange interaction between the Nd-4f state and O-2p, Zn-4s, and Zn-3p states. These findings imply that Nd-doped ZnO may be a promising material for DMS spintronic devices. Full article

The time-resolved CIDNP method can provide information about degenerate exchange reactions (DEEs) involving short-lived radicals. In the temperature range from 8 to 65 °C, the DEE reactions of the guanosine-5′-monophosphate anion GMP(-H)⁻ with the neutral radical GMP(-H)^•, of the N-acetyl tyrosine anion N-AcTyrO⁻ with a neutral radical N-AcTyrO^•, and of the tyrosine anion TyrO⁻ with a neutral radical TyrO^• were studied. In all the studied cases, the radicals were formed in the reaction of quenching triplet 2,2′-dipyridyl. The reorganization energies were obtained from Arrhenius plots. The rate constant of the reductive electron transfer reaction in the pair GMP(-H)^•/TyrO⁻ was determined at T = 25 °C. Rate constants of the GMP(-H)^• radical reduction reactions with TyrO⁻ and N-AcTyrO⁻ anions calculated by the Marcus cross-relation differ from the experimental ones by two orders of magnitude. The rate constants of several other electron transfer reactions involving GMP(-H)⁻/GMP(-H)^•, N-AcTyrO⁻/N-AcTyrO^•, and TyrO⁻/TyrO^• pairs calculated by cross-relation agree well with the experimental values. The rate of nuclear paramagnetic relaxation was found for the 3,5 and β-protons of TyrO^• and N-AcTyrO^•, the 8-proton of GMP(-H)^•, and the 3,4-protons of DPH^• at each temperature. In all cases, the dependences of the rate of nuclear paramagnetic relaxation on temperature are described by the Arrhenius dependence. Full article

The magnetic structure and the origin of band gap opening for Ba₂CuOsO₆ were investigated by exploring the spin exchange interactions and employing the spin–orbit coupling effect. It revealed that the double-perovskite Ba₂CuOsO₆, composed of the 3d (Cu²⁺) and 5d (Os⁶⁺) transition metal magnetic ions is magnetic insulator. The magnetic susceptibilities of Ba₂CuOsO₆ obey the Curie–Weiss law, with an estimated Weiss temperature of −13.3 K, indicating AFM ordering. From the density functional theory approach, it is demonstrated that the spin exchange interaction between Cu ions plays a major role in exhibiting an antiferromagnetic behavior in the Ba₂CuOsO₆ system. An important factor to understand regarding the insulating behavior on Ba₂CuOsO₆ is the structural distortion shape of OsO₆ octahedron, which should be closely connected with the ionic size of the A-site ion. Since the d-block of Os⁶⁺ (d²) ions of Ba₂CuOsO₆ is split into four states (xy < xz, yz < x²–y² < z²), the crucial key is separation of doubly degenerated xz and yz levels to describe the magnetic insulating states of Ba₂CuOsO₆. By orbital symmetry breaking, caused by the spin–orbit coupling, the t_2g level of Os⁶⁺ (d²) ions is separated into three sublevels. Two electrons of Os⁶⁺ (d²) ions occupy two levels of the three spin–orbit-coupled levels. Since Ba₂CuOsO₆ is a strongly correlated system, and the Os atom belongs to the heavy element group, one speculates that it is necessary to take into account both electron correlation and the spin–orbit coupling effect in describing the magnetic insulating states of Ba₂CuOsO₆. Full article