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Nanostructured Hybrid Magnetic Materials
Published in Ram K. Gupta, Sanjay R. Mishra, Tuan Anh Nguyen, Fundamentals of Low Dimensional Magnets, 2023
Besides these molecular magnets with static magnetism, the spin crossover (SCO) complexes are promising candidates in fabricating hybrid magnetic systems. Within such a system, the spin state of a transition metal ion can be controlled by switchable ligands [43] between high- and low-spin states under electrical or light stimuli. While the ferromagnet film contact with the LS-state molecule remains its intrinsic magnetization, the HS-state SCO molecule could significantly alter the magnetic properties, i.e., magnetic anisotropy and spin polarization. Gueddida et al. [44] demonstrated a strong magnetic coupling between the Fe(1,10-phenanthroline)2(NCS)2 (Fe-phen) molecules and Co surfaces. Despite previous encouraging work for the hybrid spinterface by SCO molecules on FM surface, many challenges remain, such as dissipation and missing of switching ability [45] due to the extremely strong interfacial coupling. These problems should be addressed in the future.
Electric Properties of Organic–Inorganic Halide Perovskites and Their Role in the Working Principles of Perovskite-Based Solar Devices
Published in Giacomo Giorgi, Koichi Yamashita, Theoretical Modeling of Organohalide Perovskites for Photovoltaic Applications, 2017
Claudio Quarti, Domenico Di Sante, Liang Z. Tan, Edoardo Mosconi, Giulia Grancini, Alessandro Stroppa, Paolo Barone, Filippo De Angelis, Silvia Picozzi, Andrew M. Rappe
Strong spin-orbit coupling and broken inversion symmetry give rise to a Rashba-type band structure. The conduction band manifold is split into two bands of opposite spin orientations, as is the valence band manifold. The conduction and valence band manifolds can be described as J = 1/2 and S = 1/2 systems with mj = ±1/2 and ms = ±1/2 quantum numbers (Giovanni et al. 2015). Optical transitions between states of different mj and ms respond differently to circularly polarized light, depending on selection rules (Even et al. 2014; Kim et al. 2014; Umebayashi et al. 2003). The population of spin states in the conduction and valence bands can therefore be monitored using circularly polarized pump and probe pulses. These time-resolved pump-probe experiments (Giovanni et al. 2015) have shown that the spin relaxation lifetime is 10 ps for electrons and 1 ps for holes. The observed dependence of the spin relaxation time on temperature is consistent with the τ ∝ T−1/2 power law for the Elliot–Yafet mechanism (Elliott 1954; Yafet 1983), which involves intraband spin-flip scattering events.
Trace Metal Chemistry in Porewaters
Published in Herbert E. Allen, Metal Contaminated Aquatic Sediments, 2018
In contrast, Fe(II) in FeS is labile to dissociation due to the high spin state (t2g4 eg2) for Fe(II). Metals in the first transition series show both high and low spin states depending on the ligand, with the low spin state having stronger bonds and extra stability due to ligand field stabilization. Thus, for pyrite to dissolve, the disulfide ligand in pyrite must be attacked by oxidation. The best environmental oxidant for pyrite is dissolved Fe(III), not oxygen [26,39–42]. The following section discusses dissolved metal speciation in porewaters which is important to mineral dissolution and formation processes.
Synthesis and characterization of naphthaldiimine-based ruthenium(III) complexes; homogenous catalytic hydrogenation and isomerization of internal and terminal alkenes
Published in Journal of Coordination Chemistry, 2022
Ahmed M. Fathy, Mahmoud M. Hessien, Mohamed M. Ibrahim, Abd El-Motaleb M. Ramadan
Metal complexes of 4d-orbitals prefer the low spin state regardless of the ligand type. This is in agreement with the values of magnetic moments of the synthesized naphthaldimine-based Ru(III) complexes. Magnetic susceptibility measurements at 22 °C of the current Ru(III) chelates (Table 6) demonstrate the low spin state of the d5 Ru(III) in a t2g5 configuration of octahedral stereochemistry. For 1, μeff is greater than 1.73 BM, suggesting appreciable spin-orbit coupling arising from incomplete quenching of the orbital contribution to the magnetic moment [38]. For 2, 3 and 4 the values of μeff are lower than the spin only value, an indication of spin-spin interactions between the low spin neighboring RuIII centers in dimeric or polymeric structures. This decrease in the magnetic moments could also arise from extensive electron delocalization or lowering in the symmetry of ligand fields [38]. Metal complexes of 4d and 5d metals are often found below the spin-only values, ascribed to high spin-orbit coupling constants. Paramagnetism expected from the unpaired electrons alone is reduced because the spin-orbit coupling aligns the vectors L and S in opposite directions [38].
Performance of density functional theory and orbital-optimised second-order perturbation theory methods for geometries and singlet–triplet state splittings of aryl-carbenes
Published in Molecular Physics, 2020
Reza Ghafarian Shirazi, Dimitrios A. Pantazis, Frank Neese
Carbenes are highly reactive organic molecules where a neutral carbon atom has two electrons less than an octet structure [1,2]. In the language of valence bond theory, carbene centres adopt sp2 hybridisation and hence are bent. Their electronic structure and spin state multiplicity can be described in a simplified manner by assuming two electrons to be distributed in two nearly degenerate p and sp2 orbitals (Figure 1). Formation of parallel spins in this configuration results in a high-spin triplet state (S = 1), while pairing of the orbitals in the sp2 orbital leads to a singlet state (S = 0). The triplet and singlet carbenes are significantly different species both structurally and electronically. Most carbenes adopt a triplet ground state, but singlet ground state carbenes can also form, or spin-state equilibria established, through interaction with proper substituents and steric restrictions [3–6]. The significant difference in electron distribution between the two spin states results in distinctly different chemical properties and reactivity. For instance, the often higher-lying singlet state participates in reactions rather than the lower-lying triplet state. Therefore, knowledge of accurate singlet–triplet energy gaps are of high importance in carbene chemistry.
Structures and binding energies for complexations of different spin states of Ni+ and Ni2+ to aromatic molecules
Published in Molecular Physics, 2019
Boutheïna Kerkeni, Adelia J. A. Aquino, Michael R. Berman, William L. Hase
Spin multiplicities of the 3d transition metal Ni cations were determined by occupation of their 3d electrons. Ni+ with a 3d84s1 configuration has two spin-unpaired d electrons and one spin-unpaired s electron and hence spin multiplicities (2S + 1) of 4 and 2. Ni2+ with a 3d84s0 configuration has two spin-unpaired d electrons and hence spin multiplicities of 3 and 1. It should be pointed out that in transition metal systems, due to closely lying d states, energies corresponding to different spin multiplicities lie very close to each other and small perturbations can often change the relative energies of the different spin states. While there are some experimental values for transition metal(Bz)2 systems in the bulk [69], there have been no experimental results on the spin multiplicities of transition metal(Bz), metal(Bz)2, metal(Np), and metal(Np)2 complexes in the gas phase.