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The magnetization processes and magnetocaloric effect (MCE) of molecular magnets are studied using the quantum Heisenberg model with the goal of finding magnetic structures with optimal magnetocaloric properties. To fulfill this goal, we examine the influence of various factors such as quantum fluctuations, the magnitude and distribution of spins, the cluster size and its geometry on the conventional (cooling) and inverse (heating) MCE. We find, surprisingly, that the best cooling and heating effects are observed in the Ising limit on the smallest possible molecular clusters represented by dimers and trimers. The increasing Heisenberg interaction suppresses both the cooling as well as heating effects, but while the heating is reduced very strongly, for relatively small values of the anisotropic Heisenberg constant, the cooling effects are reduced only weakly. Since the heating effect is undesired in low-temperature refrigeration, the Heisenberg limit is also interesting from a practical point of view. Moreover, we find that spin distributions also have a significant influence on the magnetocaloric properties of molecular magnets. Specifically, configurations with large spins on the edges of the finite chain significantly enhance the cooling effect. [ABSTRACT FROM AUTHOR]

The electronic system of molecular-based magnets is promising for use in quantum computing devices. Magnetic resonance techniques are used for magnetization manipulation and coherence tracking. The complexes [n-Bu4N]2[Cu(opba)] and [n-Bu4N]2[Ni(opba)] have been studied by 1H NMR technique using different pulse protocols. It is shown that the interpulse delay shift and phase cycling approaches are applicable in 1H NMR, but it's not as efficient as they are in EPR. Since many nuclei positions completely suppress the unwanted echo contribution, the subensembles including the longitudinal magnetization evolution should be considered. [ABSTRACT FROM AUTHOR]

One-dimensional (1D) magnetic systems offer rich phenomena in the quantum limit, proving more chemically accessible than zero-dimensional or higher-dimensional frameworks. Single-walled carbon nanotubes (SWCNT) have recently been used to encapsulate trimetric nickel(II) acetylacetonate [Nanoscale, 2019, 11, 10615–10621]. Here, we investigate the magnetization on spin chains based on nickel trimers by Matrix Product State (MPS) simulations. Our findings reveal plateaus in the exchange/magnetic-field phase diagram for three coupling configurations, showcasing effective dimeric and trimeric spin-ordering with similar or staggered entanglement across chains. These ordered states allow the qubit-like tuning of specific local magnetic moments, exhibiting disengagement or uniform coupling in entanglement plateaus. This behavior is consistent with the experimental transition from frustrated (3D) to non-frustrated (1D) molecules, corresponding to large and smaller SWCNT diameters. Our study offers insights into the potential of 1D-confined trimers for quantum computation, extending beyond the confinement of trimetric nickel-based molecules in one dimension. [ABSTRACT FROM AUTHOR]

We begin by reviewing the early developments in the synthesis of high-spin organic molecules and the simultaneous rationalization of the ground states of high spin. A number of chemists contributed, most notably Gomberg and Hückel, and theoreticians like Coulson, Rushbrooke, Longuet-Higgins, McConnell, Hoffmann etc. The subject achieved maturity after 1970. Theoretical advances were made. Methods of calculations such as multi-configuration self-consistent-field, coupled cluster, density functional, and broken-symmetry methodologies prospered. These were in turn increasingly used in magnetic studies on organic species. Armed with the concepts, theory, and calculational methodologies, both experimental and theoretical researches involved the design of fascinating magnetic organic molecules, especially since 2000. The effects of varying chemical structures, aromaticity, presence of heteroatoms, effects of hydrogen bonding and tautomerism, stereochemical aspects, and the formation of polymers, extended systems and crystals were all considered. A multitude of applications was found in the form of single molecule magnets, photomagnets and photomagnetic switches, spin cross-over, excitation and redox process assisted magnetic activation, spintronics, and so on. A spectacular growth in applications has been witnessed in the last decade. It has been accompanied by speculative and predictive advances in theory and computational investigation.

Nanostructures, fabricated by locating molecular building blocks in well-defined positions, for example, on a lattice, are ideal platforms for studying atomic-scale quantum effects. In this context, STM data obtained from self-assembled Bis(phthalocyaninato) Terbium (III) (TbPc2) single-molecule magnets on various substrates have raised questions about the conformation of the TbPc2 molecules within the lattice. In order to address this issue, molecular dynamics simulations were carried out on a 2D assembly of TbPc2 molecules. The calculations are in excellent agreement with the experiment, and thus improve our understanding of the self-assembly process. In particular, the calculated electron density of the molecular assembly compares well with STM contrast of self-assembled TbPc2 on Au(111), simultaneously providing the conformation of the two Pc ligands of the individual double-decker molecule. This approach proves valuable in the identification of the STM contrast of LnPc2 layers and could be used in similar cases where it is difficult to interpret the STM images of an assembly of molecular complexes. [ABSTRACT FROM AUTHOR]

The energy spectra and low-temperature magnetic properties of two one-dimensional Heisenberg mixed spin (s = 1, 1/2) systems, namely decorated two-leg mixed spin ladders with the lattice topology of polyacene, are studied. The gapless character of the exact excitation energy spectra for both ladder models has been determined. We found numerically that the model with macroscopic ground state spin S0 has gapped excitations with the spin S > S0. This leads to the appearance of an intermediate plateau in field dependence of magnetization at low temperatures. We have shown that the ladder with equal coupling in legs has the maximal size of this plateau at the same coupling in rungs. For a mixed spin ladder model with Ising interactions in legs, the appearance of two intermediate magnetization plateaus at low temperatures and some values of coupling parameters was shown. [ABSTRACT FROM AUTHOR]

One-dimensional (1D) magnetic systems offer rich phenomena in the quantum limit, proving more chemically accessible than zero-dimensional or higher-dimensional frameworks. Single-walled carbon nanotubes (SWCNT) have recently been used to encapsulate trimetric nickel(II) acetylacetonate [Nanoscale, 2019, 11, 10615–10621]. Here, we investigate the magnetization on spin chains based on nickel trimers by Matrix Product State (MPS) simulations. Our findings reveal plateaus in the exchange/magnetic-field phase diagram for three coupling configurations, showcasing effective dimeric and trimeric spin-ordering with similar or staggered entanglement across chains. These ordered states allow the qubit-like tuning of specific local magnetic moments, exhibiting disengagement or uniform coupling in entanglement plateaus. This behavior is consistent with the experimental transition from frustrated (3D) to non-frustrated (1D) molecules, corresponding to large and smaller SWCNT diameters. Our study offers insights into the potential of 1D-confined trimers for quantum computation, extending beyond the confinement of trimetric nickel-based molecules in one dimension.

Nitronyl nitroxides are functional building blocks in cutting‐edge research fields, such as the design of molecular magnets, the development of redox and photoswitchable molecular systems and the creation of redox‐active components for organic and hybrid batteries. The key importance of the nitronyl nitroxide function is to translate molecular‐level‐optimized structures into nano‐scale devices and new technologies. In spite of great importance, efficient and versatile synthetic approaches to these compounds still represent a challenge. Particularly, methods for the direct introduction of a nitronyl nitroxide moiety into aromatic systems possess many limitations. Here, we report gold derivatives of nitronyl nitroxide that can enter Pd(0)‐catalysed cross‐coupling reactions with various aryl bromides, affording the corresponding functionalized nitronyl nitroxides. Based on the high thermal stability and enhanced reactivity in catalytic transformation, a new reagent is suggested for the synthesis of radical systems via a universal cross‐coupling approach. [ABSTRACT FROM AUTHOR]

To understand how polyethyleneimine (PEI), as a ligand, affects structure and properties of the transition metals hexacyanoferrates (HCFs) immobilized in cross-linked PEI matrix, we have synthesized Cu(II), Zn(II), and Fe(III) HCFs via successive ion-exchange reactions with metal salts and K4[FeII(CN)6] or K3[FeIII(CN)6]. The structure and properties of the obtained materials in comparison with the crystalline HCF analogs were investigated with FT-IR, Mössbauer, and UV–Vis spectroscopy. Complete reduction of Fe(III) to Fe(II) by PEI in HCF(III) was confirmed. When synthesis was performed at pH favoring binding of precursor metal ions by PEI, cyano-bridged hybrids rather than polymer—HCFs composites were formed. Although the obtained hybrids did not demonstrate sorption activity toward cesium ions, known for crystalline HCFs, they are of interest for the other applications. SQUID measurements revealed a significant difference in magnetic properties of PEI–HCFs hybrids in comparison with crystalline HCFs. Due to the Fe(III) to Fe(II) reduction in HCF ions, Cu(II) and Fe(III) HCFs(III) lost the molecular magnets properties in PEI matrix, but magnetic ordering, including ferromagnet-antiferromagnet interactions, was observed in all hybrids over the broad temperature range. [ABSTRACT FROM AUTHOR]

Magnetoactive coordination compounds exhibiting bi- or multistability between two or more magnetic stable states present an attractive example of molecular switches. Currently, the research is focused on molecular nanomagnets, especially single molecule magnets (SMMs), which are molecules, where the slow relaxation of the magnetization based on the purely molecular origin is observed. Contrary to ferromagnets, the magnetic bistability of SMMs does not require intermolecular interactions, which makes them particularly interesting in terms of application potential, especially in the high-density storage of data. This paper aims to introduce the readers into a basic understanding of SMM behaviour, and furthermore, it provides an overview of the attractive Co(II) SMMs with emphasis on the relation between structural features, magnetic anisotropy, and slow relaxation of magnetization in tetra-, penta-, and hexacoordinate complexes. [ABSTRACT FROM AUTHOR]

The adsorption of the radical α,γ-bisdiphenylene-β-phenylallyl (BDPA) molecule to the Cu(100) surface was studied using scanning tunnelling microscopy (STM), scanning tunnelling spectroscopy (STS), and density functional theory (DFT) calculations accounting for dispersion forces. BDPA on Cu(100) was observed to align preferentially along [[EQUATION]] directions due to weak Cu-C chemisorption between fluorenyl carbons with the underlying copper atoms. The curved shape of the BDPA molecule on Cu(100) can be ascribed to the lack of molecular orbital character on the phenyl substituent. A Kondo-like feature from differential conductance (dI/dV) measurements centered close to the Fermi energy ([[EQUATION]]) suggests the retention of an electron spin-½ state, which is corroborated by hybrid DFT calculations that place the SOMO below and SUMO above EF for Cu(100)., (© 2024 Wiley‐VCH GmbH.)

Nanostructures, fabricated by locating molecular building blocks in well-defined positions, for example, on a lattice, are ideal platforms for studying atomic-scale quantum effects. In this context, STM data obtained from self-assembled Bis(phthalocyaninato) Terbium (III) (TbPc2) single-molecule magnets on various substrates have raised questions about the conformation of the TbPc2 molecules within the lattice. In order to address this issue, molecular dynamics simulations were carried out on a 2D assembly of TbPc2 molecules. The calculations are in excellent agreement with the experiment, and thus improve our understanding of the self-assembly process. In particular, the calculated electron density of the molecular assembly compares well with STM contrast of self-assembled TbPc2 on Au(111), simultaneously providing the conformation of the two Pc ligands of the individual double-decker molecule. This approach proves valuable in the identification of the STM contrast of LnPc2 layers and could be used in similar cases where it is difficult to interpret the STM images of an assembly of molecular complexes.

The first X‐band EPR spectrum containing only non‐overlapping signals of septet pyridyl‐2,4,6‐trinitrene and triplet pyridylnitrenes is reported. This spectrum was recorded after photolysis of 2,4,6‐triazidopyridine in solid argon at 5 K. The zero‐field splitting (ZFS) parameters of this trinitrene as well as of intermediate triplet mononitrenes and quintet dinitrenes formed at early stages of the photolysis were determined using the combination of modern computer line‐shape spectral simulations and density functional theory (DFT) calculations. It was found that septet pyridyl‐2,4,6‐trinitrene has the record negative parameter DS = −0.1031 cm−1 among all known to date septet pyridyl‐2,4,6‐trinitrenes and may be of interest as a model multi‐qubit spin system for investigations of quantum computation processing. [ABSTRACT FROM AUTHOR]

We introduce a multiconfigurational approach to study the magnetostructural correlations in 3d2 systems. The theoretical framework represents a restricted active space self‐consistent field method, with active space optimized to the number of all non‐bonding orbitals. To demonstrate the validity and effectiveness of the method, we explore the physical properties of the trigonal bipyramidal spin‐one single‐ion magnet (C6F5)3trenVCNtBu. The obtained theoretical results show good agreement with the experimental data available in the literature. This includes measurements for the magnetization, low‐field susceptibility, continuous wave electron paramagnetic resonance, and photoluminescence spectroscopy. The proposed method may be reliably applied to a variety of 3d2 magnetic systems. To this end, and for the sake completeness, we provide detailed analytical and numerical representations for the generic Hamiltonian's effective matrix elements related to the crystal field, exchange, spin–orbit, and Zeeman interactions. [ABSTRACT FROM AUTHOR]

We present a combined experimental and theoretical study of the ultrafast transient absorption spectroscopy results of a {Ni2Dy2}‐compound in DMF, which can be considered as a prototypic molecule for single molecule magnets. We apply state‐of‐the‐art ab initio quantum chemistry to quantitatively describe the optical properties of an inorganic complex system comprising ten atoms to form the chromophoric unit, which is further stabilized by surrounding ligands. Two different basis sets are used for the calculations to specifically identify two dominant peaks in the ground state. Furthermore, we theoretically propagate the compound's correlated many‐body wavefunction under the influence of a laser pulse as well as relaxation processes and compare against the time‐resolved absorption spectra. The experimental data can be described with a time constant of several hundreds of femtoseconds attributed to vibrational relaxation and trapping into states localized within the band gap. A second time constant is ascribed to the excited state while trap states show lifetimes on a longer timescale. The theoretical propagation is performed with the density‐matrix formalism and the Lindblad superoperator, which couples the system to a thermal bath, allowing us to extract relaxation times from first principles. [ABSTRACT FROM AUTHOR]

Host–guest electron transfer (HGET) in molecular framework systems is a critical trigger for drastic functional changes in both host framework and guest. A reversible magnetic phase transition was achieved via HGET in a layered framework, [{Ru2(2,6‐F2PhCO2)4}2(BTDA‐TCNQ)] (1), where 2,6‐F2PhCO2− and BTDA‐TCNQ represent 2,6‐difluorobenzoate and bis[1,2,5]dithiazolotetracyanoquinodimethane, respectively. The guest‐free 1 with an antiferromagnetic ground state transformed into a paramagnet, [{Ru2(2,6‐F2PhCO2)4}2(BTDA‐TCNQ)]I3 (1‐I3), by adsorbing iodine (I2). The local charge distribution of [{Ru2II,III}+‐(BTDA‐TCNQ).−‐{Ru2II,II}] in 1 was reversibly modified to [{Ru2II,III}+‐(BTDA‐TCNQ)0‐{Ru2II,II}](I3−) in 1‐I3 through HGET. Theoretical calculations of 1‐I3 indicated a partial charge delocalization as [{Ru2}(1−δ)+‐(BTDA‐TCNQ)0‐{Ru2}δ+](I3−) with δ≈0.2, aided by weak ferromagnetic coupling. 1‐I3 exhibited a hundred‐fold enhancement in electrical conductivity compared to that of 1. [ABSTRACT FROM AUTHOR]

In this paper, we consider a crystal of molecular magnets interacting with four alternating magnetic fields. When a DC magnetic field applies to molecular magnets, the energy levels of molecular magnets can be recognized as a four-level system. We consider four wave mixing process in the crystal of molecular magnets, By solving the Schrödinger equation, the analytic solutions of the probe and mixing magnetic fields are obtained. We have also numerically investigated the dynamical evolution of the probe and mixing magnetic fields. The results show that probe and mixing filed periodically oscillate in the crystal of molecular magnets medium. By adjusting the frequency detuning and the intensity of the coupled magnetic fields, the storage and retrieval of microwave field can be achieved in molecular magnets. In the end, the second-order correlation function is calculated and the anti-bunching effect can be achieved in this magnetic medium. [ABSTRACT FROM AUTHOR]

Abstract We present a combined experimental and theoretical study of the ultrafast transient absorption spectroscopy results of a {Ni2Dy2}‐compound in DMF, which can be considered as a prototypic molecule for single molecule magnets. We apply state‐of‐the‐art ab initio quantum chemistry to quantitatively describe the optical properties of an inorganic complex system comprising ten atoms to form the chromophoric unit, which is further stabilized by surrounding ligands. Two different basis sets are used for the calculations to specifically identify two dominant peaks in the ground state. Furthermore, we theoretically propagate the compound's correlated many‐body wavefunction under the influence of a laser pulse as well as relaxation processes and compare against the time‐resolved absorption spectra. The experimental data can be described with a time constant of several hundreds of femtoseconds attributed to vibrational relaxation and trapping into states localized within the band gap. A second time constant is ascribed to the excited state while trap states show lifetimes on a longer timescale. The theoretical propagation is performed with the density‐matrix formalism and the Lindblad superoperator, which couples the system to a thermal bath, allowing us to extract relaxation times from first principles.

Nonvolatile memories have attracted a lot of interest because they retain the data when the power is interrupted. Smaller size and improved performance of nonvolatile memories are pursued both for basic research and applications. In this work, a molecular wire made of seamless junctions between semiconducting single‐walled carbon nanotubes (SWNT) and partially unzipped segments of the SWNTs are reported. This novel nanostructure is demonstrated to be a nonvolatile memory, which works at room temperature under atmospheric conditions. The characteristics of the device are measured with a four‐terminal configuration and a non‐local voltage (Vnon‐local) is used as the storage signal. An electrical hysteresis of Vnon‐local is observed, wherein two states with different Vnon‐local can be switched by the application of an electric field through an insulating gate device structure, exhibiting nonvolatile characteristics. Vnon‐local can be modulated with external magnetic fields and the mechanism of the electrical hysteresis is attributed to the magnetic moments at the partially unzipped SWNT. The smaller size of SWNT and high working temperature may lead to the development of molecular nanomagnets as nonvolatile memory devices for practical applications. [ABSTRACT FROM AUTHOR]

Comprehensive Summary: Molecules with long preserved magnetic moments are perceived as the smallest units for storing bytes, which could bring a new revolution for information technology. However, the rational design of such molecules remains challenging. Here two rigid adamantanol ligand based dysprosium(III) complexes ([Dy(1‐AdO)2(py)5]BPh4 ‐ 1 and [Dy(2‐AdO)2(py)5]BPh4 ‐ 2) with pentagonal‐bipyramidal coordination geometry and local D5h symmetry were successfully prepared, which display excellent single‐molecule magnet (SMM) behavior (Ueff ≈ 1835 K, TBZFC ≈ 24 K, TB100s ≈ 17 K and TBH = 23 K for 1; Ueff ≈ 1756 K, TBZFC ≈ 20 K, TB100s ≈ 16 K and TBH = 23 K for 2) due to the much weakened vibration in low energy regimes. Remarkably, the large energy barriers and high blocking temperatures for these two complexes in solid states are well preserved in solution. This is never observed in previous studies of SMMs, indicating that the adamantanol is rigid and can be introduced to make the composed molecules stable enough to maintain the solid state magnetic property in solution. [ABSTRACT FROM AUTHOR]

Two novel salts containing the anion [Ni(mnt)2]- (mnt = maleonitriledithiolate) have been synthesized. The counter-ions, [Fe(II)(L¹ or L²)2], are cationic complexes where L¹ and L² are methylated derivatives of 2,6-bis(pyazolyl)pyridine or pyrazine, which are similar to ligands found in a series of spin-crossover (SCO) complexes. Both salts are characterized by variable temperature single crystal X-ray diffraction and bulk magnetization measurements. Compound 1, [Fe(II)(L¹)2][Ni(mnt)2]2 displays an incomplete and gradual SCO up to 300 K, followed by amore rapid increase in the high-spin fraction between 300 and 350 K. Compound 2, [Fe(II)(L²)2][Ni(mnt)2]2.MeNO2, shows a gradual, but more complete SCO response centered at 250 K. For compound 2, the SCO is confirmed by variable temperature Mössbauer spectroscopy. In both cases, the anionic moieties are isolated from each other and so no electrical conductivity is observed. [ABSTRACT FROM AUTHOR]

Three radical cation salts of BDH-TTP with the paramagnetic [ReF6]2- and diamagnetic [ReO4]- anions have been synthesized: K-(BDH-TTP)4ReF6 (1), κ-(BDH-TTP)4ReF6⋅4.8H2O (2) and pseudo-κ"-(BDH-TTP)3(ReO4)2 (3). The crystal and band structures, as well as the conducting properties of the salts, have been studied. The structures of the three salts are layered and characterized by alternating κ-(1, 2) and κ"-(3) type organic radical cation layers with inorganic anion sheets. Similar to other κ-salts, the conducting layers in the crystals of 1 and 2 are formed by BDH-TTP dimers. The partial population of positions of Re atoms and disorder in the anionic layers of 1-3 are their distinctive features. Compounds 1 and 2 show the metallic character of conductivity down to low temperatures, while 3 is a semiconductor. The ac susceptibility of crystals 1 was investigated in order to test the possible slow relaxation of magnetization associated with the [ReF6]2- anion. [ABSTRACT FROM AUTHOR]

Advances in quantum computing technology have been made in recent years due to the evolution of spin clusters. Recent studies have tended towards spin cluster subgeometries to understand more complex structures better. These molecular magnets provide a multitude of phenomena via exchange interactions that allow for advancements in spintronics and other magnetic system applications due to the possibility of increasing speed, data storage, memory, and stability of quantum computing systems. Using the Heisenberg spin-spin exchange Hamiltonian and exact diagonalization, we examine the evolution of quantum energy levels and thermodynamic properties for various spin configurations and exchange interactions. The XXYY quantum spin tetramer considered in this study consists of two coupled dimers with exchange interactions a1 J and a'1 J and a dimer--dimer exchange interaction a2 J. By varying spin values and interaction strengths, we determine the exact energy eigenstates that are used to determine closed-form analytic solutions for the heat capacity and magnetic susceptibility of the system and further analyze the evolution of the properties of the system based on the parameter values chosen. Furthermore, this study shows that the Schottky anomaly shifts towards zero as the ground-state of the system approaches a quantum phase transition between spin states. Additionally, we investigate the development of phase transitions produced by the convergence of the Schottky anomaly with both variable exchange interactions and external magnetic field. [ABSTRACT FROM AUTHOR]

• Zero field ESR line corresponds to spin transitions in singlet states of Mn3+ ions. • Power saturation of zero field ESR line is sensitive to crystal chirality. • Low frequency magnetic relaxation corresponds to magnetic solitons. • ESR line centered at zero field corresponds to intermediate phase. • Chirality affects magnetic relaxation in X-band and low frequency regions. Chiral molecular magnets are important platforms for investigation of non-linear spin phenomena. Mapping of imaginary and real parts of magnetic susceptibility in coordinates field-temperature revealed two spin transitions at 15 K and 21 K in chiral 2D metal–organic ferrimagnet [MnII(HL-pn)(H 2 O)][MnIII(CN) 6 ]•2H 2 O titled Brown Needle crystals. Curie temperature corresponds to 21 K, while the transition between ferrimagnetic and spin canting incommensurate phase happens at 15 K. We found that the second and third harmonics of non-linear magnetic susceptibility correspond to time irreversible domain walls displacement. High frequency spin relaxation was monitored by electron spin resonance (ESR) technique. Resonant line at zero field was analyzed in the frame of formalism developed for non-Kramers ions coupled by dipole–dipole interaction. The zero field ESR spectra originates from the S = 2 ground state of the Mn3+ ions. This line appears in a narrow temperature range 18–22 K indicating the intermediate magnetic phase arising in the vicinity of the Curie point. Microwave power saturation of the ESR line corresponds to a fast relaxation ∼10 ns. We found the significant difference in this relaxation time in racemic and chiral crystals. Resonant response of the Mn3+ ions controlled by dipole–dipole magnetic interaction provides very sensitive indication of crystal fields their modification and it allows one to judge on origin critical phenomena at magnetic phase transition. [ABSTRACT FROM AUTHOR]

We study the magnetic properties of the erbium based compounds, Na9[Er(W5O18)2] and [(Pc)Er{Pc{N(C4H9)2}8}]·/−, in the framework of an effective spin exchange model involving delocalized electrons occupying molecular orbitals. The calculations successfully reproduce the experimental data available in the literature for the magnetic spectrum, magnetization and molar susceptibility in dc and ac fields. Owing to their similar molecular geometry, the compounds’ magnetic behaviors are interpreted in terms of the same set of active orbitals and thus the same effective spin coupling scheme. For all three complexes, the model predicts a prompt change in the ground state from a Kramer’s doublet at zero fields to a fully polarized quartet one brought about by the action of an external magnetic field without Zeeman splitting. This alteration is attributed to the enhancement of the effect of orbital interactions over the spin exchange as the magnitude of the external magnetic field increases.

Two novel salts containing the anion [Ni(mnt)2]− (mnt = maleonitriledithiolate) have been synthesized. The counter-ions, [Fe(II)(L1 or L2)2], are cationic complexes where L1 and L2 are methylated derivatives of 2,6-bis(pyazolyl)pyridine or pyrazine, which are similar to ligands found in a series of spin-crossover (SCO) complexes. Both salts are characterized by variable temperature single crystal X-ray diffraction and bulk magnetization measurements. Compound 1, [Fe(II)(L1)2][Ni(mnt)2]2 displays an incomplete and gradual SCO up to 300 K, followed by a more rapid increase in the high-spin fraction between 300 and 350 K. Compound 2, [Fe(II)(L2)2][Ni(mnt)2]2.MeNO2, shows a gradual, but more complete SCO response centered at 250 K. For compound 2, the SCO is confirmed by variable temperature Mössbauer spectroscopy. In both cases, the anionic moieties are isolated from each other and so no electrical conductivity is observed.

Three radical cation salts of BDH-TTP with the paramagnetic [ReF6]2− and diamagnetic [ReO4]− anions have been synthesized: κ-(BDH-TTP)4ReF6 (1), κ-(BDH-TTP)4ReF6·4.8H2O (2) and pseudo-κ″-(BDH-TTP)3(ReO4)2 (3). The crystal and band structures, as well as the conducting properties of the salts, have been studied. The structures of the three salts are layered and characterized by alternating κ-(1, 2) and κ″-(3) type organic radical cation layers with inorganic anion sheets. Similar to other κ-salts, the conducting layers in the crystals of 1 and 2 are formed by BDH-TTP dimers. The partial population of positions of Re atoms and disorder in the anionic layers of 1–3 are their distinctive features. Compounds 1 and 2 show the metallic character of conductivity down to low temperatures, while 3 is a semiconductor. The ac susceptibility of crystals 1 was investigated in order to test the possible slow relaxation of magnetization associated with the [ReF6]2− anion.

We investigate the energetics and magnetic signatures of the parent molecular magnet Mn12‐Acetate [Mn12O12(COOR)16(H2O)4] and a chemically decomposed version of this structure, in which the four water molecules are converted to hydroxyl groups and hydrogen molecules. We determine electron addition and water decomposition energetics for this water‐containing molecule using density‐functional methods and include the recent Fermi‐Löwdin‐Orbital self‐interaction correction. We find that it only costs 0.32 eV to add four electrons to the parent molecule. Furthermore, due to the strong Coulomb attractions between hydroxyl anions and the Mn cations, the energy cost for breaking the four coordinating water molecules into four coordinating hydroxyls and two hydrogen molecules is decreased in the tetra‐anionic structure relative to the neutral structure. We calculate magnetic anisotropy barriers for the neutral molecule and the dehydrogenated tetra‐anion and show that large changes in the magnetic anisotropy arise the strong attraction between the hydroxyl anions and four of the crown Mn cations. We suggest that the large changes in magnetic signals associated with the [Mn12O12(COOR)16(HOH)4] to [Mn12O12(COOR)16(OH−)4 + 2H2] decomposition could provide a nondestructive spectroscopic method for learning about water decomposition mechanisms in a class of realizable model catalytic systems that have been synthesized recently. © 2019 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Novel volatile complexes of Ni(II), Co(II), Mn(II), Zn(II) with methoxy-substituted β-diketonate ligands L = (CH3)2C(OCH3)-CO-CH-CO-C(CH3)3 and LF = (CH3)2C(OCH3)-CO-CH-CO-CF3 are obtained. The novel compounds are identified by a complex of techniques, including CHF elemental, mass spectrometric, and NMR spectroscopic analyses. According to the X-ray crystallographic analysis data, in the crystals, NiL2 and ZnL2 are asymmetric binuclear complexes in which metal atoms have a different coordination environment composed of ligand oxygen atoms (c.n.= 6 and 5) and are bridged by oxygen atoms, both chelate and from one of the methoxy groups. The mixed-ligand complex [NiL(dpm)]2 (dpm = dipivaloylmethanate: 2,2,6,6-tetramethyl-3,5-heptandionate) has a similar binuclear structure. It is found that complexes with non-fluorinated ligands pass to the gas phase as monomers whereas fluorine-containing complexes pass as dimers. The compounds are paramagnetic, except zinc complexes. In the binuclear complexes based on non-fluorinated ligands, a ferromagnetic exchange interaction of magnetic moments is observed while for fluorine-containing ligands it is antiferromagnetic. [ABSTRACT FROM AUTHOR]

Highlights • A simplified uniaxial anisotropic Heisenberg model is suggested. • The model describes magnetic properties observed in a family of the Cr 7 M (M = Cd, Ni, Mn) molecular rings. • The coupling parameters of the model are all transferable among this family entities. Abstract A simplified uniaxial anisotropic Heisenberg model is proposed which describes the observed magnetic properties of a family of the Cr 7 M (M = Cd, Ni, Mn) molecular rings, and allows the determination of the coupling parameters which are all transferable among this family of molecular nanomagnets. [ABSTRACT FROM AUTHOR]

The deviation of the temperature dependence of the magnetocrystalline anisotropy in a K0.4[Cr(CN)6][Mn(S)-pn](S)-pnH0.6 uniaxial ferrimagnetic molecular magnet from the theoretical predictions for this dependence are revealed and discussed. The Dzyaloshinskii–Moriya interaction, which becomes significant at low temperatures and causes non-collinear ordering of spins, is shown to be the source of this deviation. [ABSTRACT FROM AUTHOR]

In this study, we have developed and used the advanced high-precision numerical techniques to accurately calculate the optical properties and spin structure, and access the details of spin dynamics of the cobalt octaethylporphyrin (CoOEP) in the THz pulse magnetic field. The optical spectra of CoOEP are calculated using first-principles based on the GW approximation. The optical properties, including complex dielectric function, optical reflectivity, extinction coefficient, refractive index and absorption coefficient up to 10 eV, together with the calculated spin structure are considered. The spin structure of CoOEP is described by means of the density of spin transitions within the terahertz range. The study covers both terahertz and visible ranges. On the basis of the obtained optical theoretical spectra and the spin structure of CoOEP, it can be concluded that the applied complex approach provides a detailed and accurate description of the optical properties of cobalt octaethylporphyrin within the whole range of energies. [ABSTRACT FROM AUTHOR]

Graphical abstract Intercalation of Pyridine and its halogen derivatives between layers of Ni[Ni(CN) 4 ]. Between the octahedral Ni atoms, at low temperature, a ferromagnetic interaction is established mediated by the pi-pi stacking of neighboring aromatic pyridine rings. Highlights • Magnetic interaction mediated by pi-pi stacking. • Hybrid inorganic–organic solids. • Molecular magnets. • Intercalation of pyridine and its halogen derivatives in layered tetracyanonickelates. Abstract The intercalation of pyridine and its 3-substituted halogen derivatives (L) between layers of nickel (T) tetracyanonickelate provides a beautiful example of magnetic interaction through π-π stacking. The intercalation process results in the formation of 3D solids with formula unit TL 2 [Ni(CN) 4 ]. In the interlayer region, the intercalated molecules are found coordinated to the axial positions for the metal T (Ni). Neighboring molecules remain interacting through their dipole and quadrupole moments. For a coplanar configuration of their aromatic rings, the corresponding π-π clouds appear overlapped, which makes possible the appearance of a weak ferromagnetic interaction between T metal centers, to form an ordered system of magnetic chains separated about 10 Å. The halogen substituent in the pyridine molecule modulates the π-π clouds overlapping and, in consequence, the magnetic interaction through the chain. Such interaction coexists with a weak antiferromagnetic coupling between T atoms through the CN bridges in the two dimensional system, {T[Ni(CN) 4 ]} ∝ , but at low temperature, the interaction through the π-π clouds overlapping dominates. This contribution includes the study of the magnetic properties of the layered T(H 2 O) 2 [Ni(CN) 4 ]∙xH 2 O precursor solid where the magnetic interaction takes place through the hydrogen bonding network formed by the water molecules found in the interlayer region. The magnetic properties of both series of layered solids were evaluated from low temperature SQUID measurements complemented with structural and spectroscopic information. The interpretation of the magnetic and structural data is supported by computational calculations on the intermolecular interactions in the interlayer region. [ABSTRACT FROM AUTHOR]

Advances in quantum computing technology have been made in recent years due to the evolution of spin clusters. Recent studies have tended towards spin cluster subgeometries to understand more complex structures better. These molecular magnets provide a multitude of phenomena via exchange interactions that allow for advancements in spintronics and other magnetic system applications due to the possibility of increasing speed, data storage, memory, and stability of quantum computing systems. Using the Heisenberg spin–spin exchange Hamiltonian and exact diagonalization, we examine the evolution of quantum energy levels and thermodynamic properties for various spin configurations and exchange interactions. The XXYY quantum spin tetramer considered in this study consists of two coupled dimers with exchange interactions α1J and α1′J and a dimer–dimer exchange interaction α2J. By varying spin values and interaction strengths, we determine the exact energy eigenstates that are used to determine closed-form analytic solutions for the heat capacity and magnetic susceptibility of the system and further analyze the evolution of the properties of the system based on the parameter values chosen. Furthermore, this study shows that the Schottky anomaly shifts towards zero as the ground-state of the system approaches a quantum phase transition between spin states. Additionally, we investigate the development of phase transitions produced by the convergence of the Schottky anomaly with both variable exchange interactions and external magnetic field.

Abstract The critical properties of two related bimetallic compounds {[MII(H 2 O) 2 ] 2 [NbIV(CN) 8 ]·4H 2 O} n (M = Mn, Fe) are reported. The compounds exhibit the transition to a magnetically ordered phase at T c = 43 K in the case of the Fe-based sample ( FeNb ), and at T c = 50 K for the Mn-based sample ( MnNb ). They differ in relative orientation of the M and Nb sublattices, which is parallel, i.e. ferromagnetic, in FeNb and antiparallel, i.e. ferrimagnetic, in MnNb. Critical exponents β and γ , governing the temperature dependence of the spontaneous magnetization below T c and the temperature dependence of the initial susceptibility above T c , respectively, have been determined using the Kouvel-Fisher method. Critical exponent δ has been obtained through the analysis of the critical magnetization isotherm. Thus determined values of the critical exponents were verified by employing two independent forms of the scaling equation of state. All the magnetization data are demonstrated to collapse either onto two universal branches corresponding to T 〈 T c and T 〉 T c , respectively, or onto a single universal curve. The critical exponents allow to ascribe FeNb as well as MnNb to the universality class of the three-dimensional (3D) Heisenberg model. Highlights • Critical behavior in {[MII(H 2 O) 2 ] 2 [NbIV(CN) 8 ]·4H 2 O} n (M = Mn, Fe) is studied. • The critical exponents β and γ have been determined using the Kouvel-Fisher method. • The critical exponent δ has been obtained based on critical magnetization isotherm. • The values of β and γ were verified by two forms of the scaling equation of state. • Both compounds can be assigned to the universality class of the 3D Heisenberg model. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • A series of isomorphic 1D-polymeric cyanide-bridged LnIII-CoIII complexes was prepared and studied. • Compounds formed by Dy, Er and Yb exhibit properties of field-induced SMMs. • This is the first series of cyanocobaltate-bridged SMMs formed by the entire set of heavy Kramers ions. Abstract A series of novel isomorphic 1D-polymeric complexes {[Ln(terpy)(H 2 O) 3 ][Co(CN) 6 ]·5H 2 O} n (Ln = Tb , Dy , Er , Yb ; terpy is 2,2';6',2“-terpyridine) was prepared and characterized. Compounds Dy , Er and Yb were found to exhibit properties of field-induced single-molecule magnets with the anisotropy barriers of 68 K, 8 K and 37 K, respectively. Erbium complex Er seems to represent the first known example of Er-based cyanide-bridged 3d - 4f SMM, whereas Yb is the second Yb-based one. The effect of the geometry of the coordination environment as well as of ligands field symmetry on SMM behavior of Dy , Er and Yb compounds is discussed. Among the cyanocobaltate-bridged chain complexes, the Dy , Er , Yb are the first series formed by the entire set of heavy Kramers ions which were studied as SMMs. [ABSTRACT FROM AUTHOR]

We consider the diamond chain with S = 1/2 XYZ vertical dimers which interact with the intermediate sites via the interaction of the Ising type. We also suppose all four spins form the diamond-shaped plaquette to have different g-factors. The non-uniform g-factors within the quantum spin dimer as well as the XY-anisotropy of the exchange interaction lead to the non-conserving magnetization for the chain. We analyze the effects of non-conserving magnetization as well as the effects of the appearance of negative g-factors among the spins from the unit cell. A number of unusual frustrated states for ferromagnetic couplings and g-factors with non-uniform signs are found out. These frustrated states generalize the “half-fire-half-ice” state introduced in reference Yin et al. (2015). The corresponding zero-temperature ground state phase diagrams are presented. [ABSTRACT FROM AUTHOR]