Special Issue “Spin Crossover (SCO) Research”

Abstract

This special issue, entitled "Spin Crossover (SCO) Research", illustrates the current relevance of a focused topic, which is in turn highly versatile. Indeed, the collection of papers presented constitutes a sampler that shows the topical importance of this area by attracting the interest of many top researchers and how it is approached under a multidisciplinary perspective. The guest editors are thankful to the publisher and their professional editorial team, who have helped enormously in the task of putting together this issue. The serious, altruistic, and dedicated work of all the referees is also gratefully acknowledged. Finally, the generosity and the strong scientific input of the authors that have contributed their papers with some of their best research results deserve the strongest recognition. The collection of manuscripts in this issue encompasses two high-quality review articles and eighteen outstanding research papers. Following the announced spirit of the original call, very diverse aspects of the phenomenon of spin transition are treated. Therefore, a good balance between theory, synthesis, and physical studies is encountered, while various manifestations of SCO materials are present as part of the theoretical treatments as well as experimentally (molecular, polymeric, nano-structured, and composite materials). The issue includes Monte Carlo simulations of the dynamic properties of the SCO phenomenon analyzing the influence of crystal defects [1], the surface effects [2], and the interactions within the bulk of the system using an Ising model [3]. In addition, density functional theory (DFT) calculations are employed to study the cooperativity using a very well-known experimental compound [4]. A recently published molecular system is reevaluated also by means of DFT calculations to propose novel ligand effects to the low/high spin relative stability [5], while this method is also employed in combination to nuclear inelastic scattering (NIS) data to unveil the coupling between the vibrational levels near one Fe(II) center, with the neighboring centers depending on the relative spin states [6]. This special issue also witnesses the synthesis of new SCO systems and their properties. These include a family of Fe(II) complexes with a new 4-hydroxy 1bpp ligand (1bpp; 2,6-di(pyrazol-1-yl) pyridine) [7], two derivatives of the alkyl-1H-tetrazole series, now exhibiting a propargyl function as a way to perform post-synthetic modifications of SCO compounds [8], and a novel series of Fe(III) heteroleptic molecules exhibiting varying magnetic behaviors, explained in terms of differing types of intermolecular interactions [9]. Abrupt SCO of another series of Fe(III) molecules combining imidazole and Shiff-base related ligands is also explained as a result of hydrogen bonding interactions propagated in one direction of the crystal lattice [10]. A novel Fe(II) mononuclear species made with a pyridylmethyleneaniline ligand featuring an isopropyl group exhibits hysteresis resulting from the coupling of the SCO tran...

Contribution of the Multiplicity Fluctuation in the Temperature Dependence of Phonon Spectra of Rare-Earth Cobaltites

“…Contrary to other materials with SCO with a sharp switching between HS and LS states under high pressure or heating [ 2 , 3 , 4 ], the rare-earth cobaltites demonstrate a smooth increase in the HS population due to the multiplicity fluctuations.…”

“…The close-to-spin crossover (SCO) of the high-spin (HS) and the low-spin (LS) terms of a magnetic cation, the energy of the multiplicity fluctuation , is small. The phenomenon of SCO in 3d-metal oxides is usually realized under high pressure [ 1 ], while in metal–ligand complexes in an organic matrix, the SCO may be induced by changing temperature [ 2 , 3 , 4 , 5 ]. There is also one more group of 3d-metal oxides, the rare-earth cobaltites RCoO 3 with a perovskite structure, very close to SCO [ 6 , 7 , 8 , 9 , 10 ].…”

Molecular S = 2 High-Spin, S = 0 Low-Spin and S = 0 ⇄ 2 Spin-Transition/-Crossover Nickel(II)-Bis(nitroxide) Coordination Compounds

“…A reversible spin transition between low-spin (LS) and high-spin (HS) states trig gered by external stimuli such as heat and light is named spin crossover (SCO) [1][2][3][4][5][16][17][18][19]. Iron(II) (3d 6 ) compounds are the most popular [20][21][22][23][24][25][26][27][28], since magnetic and chromic changes are drastic between S = 0 diamagnetic and S = 2 paramagnetic states. Furthermore considerable attention has been paid to room-temperature SCO [29] required for applica tions under ambient conditions.…”

Reversible Spin-State Switching and Tuning of Nuclearity and Dimensionality via Nonlinear Pseudohalides in Cobalt(II) Complexes

“…Low-dimensional multifunctional magnetic systems possess unique advantages of having chemical control over numerous physical properties. These attributes lead to amazing applications to storing and processing quantum information. , All of these fascinating systems are of great interest in the material sciences for their potential applications in switches and sensors, as the physical properties of such systems can be controlled and tuned by the application of various external stimuli. − Among those, switchable bistable materials based on transition metals have attained an enormous importance over the last few decades, particularly materials displaying magnetic or electric bistabilities such as spin crossover (SCO), − single-molecule magnets (SMMs), − single chain magnets (SCMs), − metal-to-metal electron transfer, − organic radicals, , etc. SCO materials represent emerging candidates over the past few decades offering an attractive route to the realization of molecular spintronics, molecular sensors, and nanoscale devices. − It is well-known for the SCO systems that the electronic conversion between two easily accessible low-spin (LS) and high-spin (HS) states can be tuned or manipulated in a reversible manner under a slight modification of external perturbation: e.g.…”