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Control over transition rates between spin states of emitters is crucial in a wide variety of fields ranging from quantum information science to the nanochemistry of free radicals. We present an approach to drive a both electric and magnetic dipole-forbidden transition of a spin emitter by placing it in a nanomagnonic cavity, requiring a description of both the spin emitter beyond the point dipole approximation and the vacuum magnetic fields of the nanomagnonic cavity with a large spatial gradient over the volume of the spin emitter. We specifically study the SiV$^-$ defect in diamond, whose Zeeman-split ground states comprise a logical qubit for solid-state quantum information processing, coupled to a magnetic nanoparticle serving as a model nanomagnonic cavity capable of concentrating microwave magnetic fields into deeply subwavelength volumes. Through first principles modeling of the SiV$^-$ spin orbitals, we calculate the spin transition densities of magnetic dipole-allowed and -forbidden transitions and calculate their coupling rates to various multipolar modes of the nanomagnonic cavity. We envision using such a framework for quantum state transduction and state preparation of spin qubits at GHz frequency scales., 8 pages, 4 figures

The metal-metal-bonded molecule [Bu4N][(HL)2Fe6(dmf)2] (Fe6) was previously shown to possess a thermally isolated spin S = 19/2 ground state and found to exhibit slow magnetization relaxation below a blocking temperature of ∼5 K [J. Am. Chem. Soc.2015, 137, 13949-13956]. Here, we present a comprehensive spectroscopic investigation of this unique single-molecule magnet (SMM), combining ultrawideband field-swept high-field electron paramagnetic resonance (EPR) with frequency-domain Fourier-transform terahertz EPR to accurately quantify the spin Hamiltonian parameters of Fe6. Of particular importance is the near absence of a 4th-order axial zero-field splitting term, which is known to arise because of quantum mechanical mixing of spin states on account of the relatively weak spin-spin (superexchange) interactions in traditional polynuclear SMMs such as the celebrated Mn12-acetate. The combined high-resolution measurements on both powder samples and an oriented single crystal provide a quantitative measure of the isolated nature of the spin ground state in the Fe6 molecule, as well as additional microscopic insights into factors that govern the quantum tunneling of its magnetization. This work suggests strategies for improving the performance of polynuclear SMMs featuring direct metal-metal bonds and strong ferromagnetic spin-spin (exchange) interactions.

Temperature can be used as clinical marker for tissue metabolism and the detection of inflammations or tumors. The use of magnetic resonance imaging (MRI) for monitoring physiological parameters like the temperature noninvasively is steadily increasing. In this study, we present a proof‐of‐principle study of MRI contrast agents (CA) for absolute and concentration independent temperature imaging. These CAs are based on azoimidazole substituted NiII porphyrins, which can undergo Light‐Driven Coordination‐Induced Spin State Switching (LD‐CISSS) in solution. Monitoring the fast first order kinetic of back isomerisation (cis to trans) with standard clinical MR imaging sequences allows the determination of half‐lives, that can be directly translated into absolute temperatures. Different temperature responsive CAs were successfully tested as prototypes in methanol‐based gels and created temperature maps of gradient phantoms with high spatial resolution (0.13×0.13×1.1 mm) and low temperature errors (, Temperature is a clinical marker for tissue metabolism and can be used for the detection of diseases. Besides intrinsic magnetic resonance (MR) methods for relative temperature changes, there are only limited methods for absolute temperature imaging. In this study we present an in vitro method with a photoswitchable contrast agent for absolute and concentration independent 3D temperature imaging.

The electronic and magnetic properties of armchair-hexagonal (AHEX) and zigzag-triangular (ZTRI) graphene quantum dots doped with alkali metals are investigated using density functional theory. The binding energy confirms the stability of the undoped systems. Although doping decreases stability of single layer structures, in bilayer ones the binding energy between the layers increases. The former is due to the broken bonds and the deformation at the surface, while the later is due to the chemical bonds formation between the layers. We found that the lowest ground state energy for AHEX/AHEX-doped is the singlet/quadruplet spin state. Therefore, AHEX dots experience transformation from diamagnetic to ferromagnetic state after doping. In addition, the optimized spin state for ZTRI/ZTRI-doped is the quintet/sextet spin-polarized state. In few cases, the doped AHEX/ZTRI dots have doublet/quadruplet spin state due to the strong interaction between the flake atoms that passivates some unpaired electrons. Magnetic properties depend also on stacking, for instance pristine bilayer triangular flakes become antiferromagnetic due to pairing between edge states. The energy gap significantly affected by doping, for instance the gap decreases from ~3.7 eV in hexagonal flakes to 1.5 eV when it is doped with Na in the upper position. Electrons from the broken bonds around the doped metal form orbitals loosely bound to the flake consequently decreasing the energy gap. On the other hand, stacking increases the energy gap in bilayer triangular flakes due to the mutual passivation of the reactive edge states from both the layers. The calculated spin up/down density ratio is high in hexagonal flakes leading to high spin polarization (P), for instance P = 0.64 in hexagonal flakes doped with K atom. The found enhanced spin polarization, in addition to the tunable magnetic properties, makes doped graphene flakes promising candidates for spintronic devices.

Within the multielectron model of magnetic insulator with two different spin terms at each cation and spin crossover under high pressure we have studied dynamics of a sudden excited non equilibrium spin state. We obtain the different relaxation of the magnetization, high spin/low spin occupation numbers, and the metal-oxygen bond length for different values of the external pressure. For each pressure-temperature values stationary state agrees to the mean field phase diagrams. We found the long living oscillations of magnetization for the high spin ground state at small pressure. Close to crossover pressure the smooth relaxation is accompanied with a set of sharp strongly non linear oscillations of magnetization and HS/LS occupation numbers that are accompanied by the Franck–Condon resonances.

As low-cost electrocatalysts for oxygen reduction reaction applied to fuel cells and metal-air batteries, atomic-dispersed transition metal-nitrogen-carbon materials are emerging, but the genuine mechanism thereof is still arguable. Herein, by rational design and synthesis of dual-metal atomically dispersed Fe,Mn/N-C catalyst as model object, we unravel that the O2 reduction preferentially takes place on FeIII in the FeN4 /C system with intermediate spin state which possesses one eg electron (t2g4eg1) readily penetrating the antibonding π-orbital of oxygen. Both magnetic measurements and theoretical calculation reveal that the adjacent atomically dispersed Mn-N moieties can effectively activate the FeIII sites by both spin-state transition and electronic modulation, rendering the excellent ORR performances of Fe,Mn/N-C in both alkaline and acidic media (halfwave positionals are 0.928 V in 0.1 M KOH, and 0.804 V in 0.1 M HClO4), and good durability, which outperforms and has almost the same activity of commercial Pt/C, respectively. In addition, it presents a superior power density of 160.8 mW cm−2 and long-term durability in reversible zinc–air batteries. The work brings new insight into the oxygen reduction reaction process on the metal-nitrogen-carbon active sites, undoubtedly leading the exploration towards high effective low-cost non-precious catalysts., The working mechanism of several low-cost electrocatalyst materials is still arguable. Here the authors show a model Fe,Mn/N-C catalyst where the oxygen reduction preferentially takes place on Fe(III) sites with the intermediate spin state (t2g4 eg1) caused by the adjacent Mn-N moieties.

A quantum-chemical model of the minimal cluster in xenotime has been proposed taking into account the ionic-crystal medium potential. The [YO8]5– cluster includes oxygen atoms from six phosphate anions. Owing to the breaking of the covalent P–O bonds, each oxygen atom contributes one unpaired electron to the cluster. The spin state is characterized by a zero ‹Ŝ› vector and a doubled dispersion D = 2 (‹Ŝ2› – ‹Ŝ›2) = 7.98 a. u. Structure of the [YO8]5– cluster does not favour the replacement of yttrium(III) with thorium(III) or uranium(III). The simulations have been performed via the DFT method using the (U)PBE0 functional.

In this work, we present a master equation approach to simulating DC transport through single electron transistors and quantum dots suitable for an upper-division undergraduate computational physics project. After introducing the basic theory describing transport through quantum dots, we present a simulation of the simple case of a metallic dot including effects due to the finite temperature of the leads. Building on this example, we simulate published data with orbital and spin states. We envision students building on these simulations to replicate other data in the published literature. Projects of this type would be suitable for an undergraduate independent study or computational project and will give students a strong introduction to the topic of transport through quantum dots without the need for expensive cryogenic and electrical measurement systems or device fabrication necessary for experimental work.

Polycrystalline LaMn1-xCoxO3 (0.1≤ x ≤ 0.5) samples were synthesized using conventional ceramic method. Rietveld refined X-ray diffraction pattern revealed the single-phase orthorhombic crystal structure of all the samples with the space group Pbnm. Temperature-dependent magnetic measurements performed in field cooled (FC) and zero field cooled (ZFC) mode at 102 Oe exhibit the onset of double transition in x = 0.3–0.5 compositions. The ordering temperature rises with an increase in Co concentration. FC and ZFC studies show the presence of glassy state below the ordering temperature in all samples; confirmed using a. c. susceptibility measurements. The a. c. susceptibility data are analyzed using power law and the existence of canonical spin glass is revealed. Magnetic hysteresis studies demonstrate the enhanced ferromagnetism amid the presence of unsaturated magnetization with an increase in Co doping. The presence of double transition and spin glass state is attributed to the competing ferromagnetic and anti-ferromagnetic interactions between the Co and Mn ions present in the system. The system also depicts the presence of appreciable value of magnetoresistance ~42% at 8 T magnetic field in x = 0.5 sample. These properties are interpreted through valence and spin states of Mn and Co ions, being confirmed from electronic structure studies using X-ray absorption spectroscopy (XAS) at L3,2- edges of respective ions along with O K-edge for all samples (0.1≤ x ≤ 0.5). After meticulous analysis and conjoining the results obtained from magnetization and XAS studies, it is found that cobalt is present in high spin Co2+ and high/low spin Co3+-state. Charge transfer multiplet calculation done at L3,2 edges of Mn and Co ions confirm the presence of Mn3+/Mn4+ and Co2+/Co3+ states consistent with XAS results. X-ray photoelectron spectroscopy performed at Mn2p, Co2p, and O1s -edges further substantiate the reasons behind the properties exhibited by the present system.

The response of the spin state to in situ variation of the coordination number (CISSS) is a promising and viable approach to smart sensor materials, yet it suffers to date from insensitive detection. Herein, we present the synthetic access to a family of planar nickel(II) complexes, whose CISSS is sensitively followed by means of fluorescence detection. For this purpose, nickel(II) complexes with four phenazine-based Schiff base-like ligands were synthesized and characterized through solution-phase spectroscopy (NMR and UV-vis), solid-state structure analysis (single-crystal XRD), and extended theoretical modeling. All of them reveal CISSS in solution through axial ligating a range of N- and O-donors. CISSS correlates nicely with the basicity of the axial ligand and the substitution-dependent acidity of the nickel(II) coordination site. Remarkably, three out of the four nickel(II) complexes are fluorescent in noncoordinating solvents but are fluorescence-silent in the presence of axial ligands such as pyridine. As these complexes are rare examples of fluorescent nickel(II) complexes, the photophysical properties with a coordination number of 4 were studied in detail, including temperature-dependent lifetime and quantum yield determinations. Most importantly, fluorescence quenching upon adding axial ligands allows a "black or white", i.e. digital, sensoring of spin state alternation. Our studies of fluorescence-detected CISSS (FD-CISSS) revealed that absorption-based CISSS and FD-CISSS are super proportional with respect to the pyridine concentration: FD-CISSS features a higher sensitivity. Overall, our findings indicate a favored ligation of these nickel(II) complexes in the excited state in comparison to the ground state.

Molecular catalysts have been extensively studied for fundamental understanding of the catalytic mechanism of specific active sites for carbon dioxide (CO2) reduction, and nitrogen-coordinated tran...

Rashba spin-orbit coupling enables electric control of spin states, promising enormous advances from conventional charge-based computing. Until now, a general scheme or a descriptor to find an optimal system with isolated spin states with large tunable splitting is still lacking. Here, based on first-principles calculations, we explore the microscopic physicochemical mechanism responsible for the Rashba effect in 2D van der Waals heterobilayers. We find that the difference in the Born effective charge of atoms at the interface can be used as a single-layer descriptor to predict heteropairs with large Rashba splitting, thus reducing the scaling factor in materials search. Moreover, we discover that for most 2D materials, the routinely used Rashba parameter αR is not a good gauge of the effect's strength. From our general scheme, MoTe2|Tl2O and MoTe2|PtS2, with spin splitting above 120 meV, Rashba energy ER = 94 meV, and wavenumber difference 2k0 = 0.36 A-1 ("effective" αR > 1 eVA), emerge as the best candidates for spin transistors at room temperature.

Cerium (Ce) plays important roles in catalysis. Its position in the sixth period of the periodic table leads to spin-orbit coupling (SOC) and other open-shell effects that make the quantum mechanical calculation of cerium compounds challenging. In this work, we investigated the low-lying spin states of Ce+ and the bond energy of CeH+, both by multiconfigurational methods, in particular, SA-CASSCF, MC-PDFT, CASPT2, XMS-PDFT, and XMS-CASPT2, and by single-configurational methods, namely, Hartree-Fock theory and unrestricted Kohn-Sham density functional theory with 34 choices of the exchange-correlation functional. We found that only CASPT2, XMS-CASPT2, and SA-CASSCF (among the five multiconfigurational methods) and GAM, HCTH, SOGGA11, and OreLYP (among the 35 single-configuration methods) successfully predict that the SOC-free ground spin state of Ce+ is a doublet state, and CASPT2 and GAM give the most accurate multireference and single-reference calculations, respectively, of the excitation energy of the first SOC-free excited state for Ce+. We calculated that the ground doublet state of Ce+ is an intra-atomic hyper-open-shell state. We calculated the spin-orbit energy (ESO) of Ce+ by the five multiconfigurational methods and found that ESO calculated by CASPT2 is the closest to the experimental value. Taking advantage of the availability of an experimental D0 for CeH+ as a way to provide a unique test of theory, we showed that all the multiconfigurational methods overestimate D0 by at least 246 meV (5.7 kcal/mol), and only three functionals, namely, SOGGA, MN15, and GAM, have an error of D0 that is less than 200 meV (5 kcal/mol).

We propose an entanglement-creation scheme in a multi-atom ensemble trapped in an optical cavity, named entanglement amplification, converting unentangled states into entangled states and amplifying less-entangled ones to maximally entangled Greenberger-Horne-Zeilinger (GHZ) states whose fidelity is logarithmically dependent on the atom number and robust against common experimental noises. The scheme starts with a multi-atom ensemble initialized in a coherent spin state. By shifting the energy of a particular Dicke state, we break the Hilbert space of the ensemble into two isolated subspaces to tear the coherent spin state into two components so that entanglement is introduced. After that, we utilize the isolated subspaces to further enhance the entanglement by coherently separating the two components. By single-particle Rabi drivings on atoms in a high-finesse optical cavity illuminated by a single-frequency light, 2000-atom GHZ states can be created with a fidelity above 80% in an experimentally achievable system, making resources of ensembles at Heisenberg limit practically available for quantum metrology.

The ability of cobalt to take, depending on the temperature, pressure, and doping, various charge and spin states in oxide compounds periodically becomes the topic of scientific controversy and is a frequent cause of ambiguity in the interpretation of experimental results. In this review, we will discuss cobaltites, i.e., oxide compounds of cobalt, in which cobalt is in an oxidation state (charge state) of 3+. In these compounds, Co3+ ions can take the following spin configurations: high-spin, low-spin, and intermediate-spin configurations. The conditions for the formation of various spin states are given on the basis of the Tanabe–Sugano diagrams. It is shown how X-ray spectral methods, such as X-ray photoelectron spectroscopy, X-ray emission spectroscopy, X-ray absorption spectroscopy, and X-ray magnetic dichroism, can be used to study cobaltites. By using Co L2,3 X-ray absorption spectra that have a rich structure, one can determine the charge and spin states of cobalt ions. These spectra can be reproduced by atom-like multiplet calculations that involve many electrons and use the energy splitting of atomic orbitals by the ligand field as a free parameter. Absorption K spectra of oxygen are of a band nature, i.e., these spectra can be used, by mixing the 3d states of cobalt with the 2p states of oxygen, to estimate the spin state of cobalt ions and to analyze cobaltite phases after external influences. It is shown that the spin states of cobalt ions can be determined from Co Kβ X‑ray emission spectra (electronic transition $$3p \to 1s$$ ) that are sensitive to the spin state of 3d electrons because of the strong exchange interaction between the 3p hole and 3d orbitals in the final state of the emission process. A classic example of cobaltites with a low-spin configuration of cobalt ions is lithium cobaltite LiCoO2 that is a well-known material for power source cathodes. The nature of holes in defective cobaltites of the LixCoO2 (x < 1) type is considered. It is shown that holes arising from defects in the lithium sublattice are of an oxygen nature. In cobaltite LaCoO3 that also contains trivalent cobalt ions, a transition from a low-spin state to a high-spin state occurs at temperatures above 90 K. The feasibility of an intermediate-spin state in this compound is also considered. The results of X-ray spectral studies of double substitution perovskites Ln1 – xAxCo1 – yMyO3 (Ln is a lanthanide, A is Ca or Sr, and M is a transition element) are given, and changes in the charge states of cobalt ions upon doping of perovskites are shown. The results of experimental determination of spin states in octahedrons and pyramids of cobaltites LnBaCo2O6 – δ ( $$0 \leqslant \delta \leqslant 1$$ ) at temperatures below and above the temperature of the metal-insulator transition are systematized. Methods for determining spin states on the basis of X-ray spectral data are discussed. It is shown in the last section of the article how the charge state and concentration of cobalt ions in doped layered cobaltites LnBaCo4O7 can be determined using X-ray absorption spectroscopy. In these compounds, cobalt ions are in tetrahedral positions and, consequently, trivalent cobalt ions should be exclusively in the high-spin state.

We combine old and new quantum field theoretic arguments to show that any theory of stable or metastable higher spin particles can be coupled to gravity only when the gravity sector has a stringy structure. Metastable higher spin particles, free or interacting, cannot couple to gravity while preserving causality unless there exist higher spin states in the gravitational sector much below the Planck scale $M_{\rm pl}$. We obtain an upper bound on the mass $\Lambda_{\rm gr}$ of the lightest higher spin particle in the gravity sector in terms of quantities in the non-gravitational sector. We invoke the CKSZ uniqueness theorem to argue that any weakly coupled UV completion of such a theory must have a gravity sector containing infinite towers of asymptotically parallel, equispaced, and linear Regge trajectories. Consequently, gravitational four-point scattering amplitudes must coincide with the closed string four-point amplitude for $s,t\gg1$, identifying $\Lambda_{\rm gr}$ as the string scale. Our bound also implies that all metastable higher spin particles in 4d with masses $m\ll \Lambda_{\rm gr}$ must satisfy a weak gravity condition., Comment: 37 pages + appendices, multiple figures

The Monte Carlo method was used to calculate the relative dispersions of the magnetization Rm, susceptibility Rχ, and heat capacity RC for a weakly diluted impurity Potts model with the number of spin states q = 4. It is shown that the introduction of disorder in the form of nonmagnetic impurities into the two-dimensional Potts model with q = 4 on square lattice leads to nonzero values for Rm, Rχ, and RC at the critical point.

Mononuclear and dinuclear iron complexes are found as key intermediates in many synthetic and biocatalytic reactions, since many of these species are transient and have high catalytic abilities. However, there is still demanding and challenging to theoretical study on structures, bonding, magnetic interactions and reactivity of iron species. Here, we have discussed a detailed computational study on Fe(III/IV/V)–O/O2 and Fe(IV)–μ-O/O2–Fe(IV) species using a dispersion-corrected (B3LYP-D2) density functional method. By computing all the possible spin states for these species, we have predicted the ground state and structure-function relationships in their ground states and analyzed the bonding aspects of these species on employing MO analysis. We have also discussed the shifting of iron centers out of the plane and magnetic coupling between iron and iron/oxygen centers. A computed significant spin density on the oxygen can be a witness for reactivity during the C–H and O–H bond activation. Our DFT studies are also in general agreement with the available experimental data.

Reversible water molecule-induced spin state inter-conversion for the mononuclear cobalt(II) complex [Co(terpy)2]I2·2H2O (1, terpy = 2,2′:6′,2′′-terpyridine) is reported along with its co-crystalli...

The spin state of antibonding orbital (eg) occupancy in LaCoO3 is recognized as a descriptor for its oxygen electrocatalysis. However, the Co(III) cation in typical LaCoO3 (LCO) favors low spin state, which is mediocre for absorbing oxygen-containing groups involved in oxygen evolution reaction (OER) and oxygen reduction reaction (ORR), thus hindering its further development in electrocatalysis. Herein, both experimental and theoretical results reveal the enhancement of bifunctional electrocatalytic activity in LaCoO3 by N doping. More specifically, electron energy loss spectroscopy and superconducting quantum interference devices magnetic analysis demonstrate that the Co(III) cation in N-doped LaCoO3 (LCON) achieves a moderate eg occupancy (≈1) compared with its low spin state in LaCO3. First-principle calculation results reveal that N dopants play a bifunctional role of tuning the spin-state transition of Co(III) cations and increasing the electrical conductivity of LCO. Thus, the optimized LCON exhibits an OER overpotential of 1.69 V at the current density of 50 mA/cm2 (1.94 V for pristine LCO) and yields an ORR limiting current density of 5.78 mA/cm2 (4.01 mA/cm2 for pristine LCO), which offers a new strategy to simultaneously modulate the magnetic and electronic structures of LCO to further enhance its electrocatalytic activity.

Relativistic effects are quite large for the actinide 5f and 6d open shells, and in the present study we present combinatorial enumeration of $$\upomega {{-}} \upomega $$ states of all 14 actinide (lanthanide) dimers using multinomial symmetric function (S-function) techniques. The techniques presented here enumerate all possible $$\upomega {{-}} \upomega $$ states that arise from relativistic 2-component molecular spinors composed of the 7s, 6d 5f, and possibly 7p shells of the actinide dimers Th2 through Lr2. The combinatorial enumerations techniques reveal that that for Americium dimer (Am2) there are 20,058,300 S-function terms of which only 616,227 terms satisfy the Pauli exclusion principle yielding 401,166,110 $$\upomega {{-}} \upomega $$ states (142.6 MB of output), all of which arise from primarily the 7s/6d/5f shells of Am. Explicit tables are constructed for the relativistic $$\upomega {{-}} \upomega $$ states for Th2 to Am2 with several restrictions imposed on the levels of excitations primarily to reduce the table sizes, and through the electron–hole equivalence $$\upomega {{-}} \upomega $$ states of the remaining dimers of the actinide row are enumerated. The computational and mathematical techniques also enumerate the $$\upomega {{-}} \upomega $$ states of Ce2 to Eu2 and by electron–hole equivalence Gd2 to Tm2, although spin–orbit splittings are smaller for lanthanides. A unique feature of the present combinatorial technique is that it facilitates any number of orbitals and any number of open shells including the possibility of 14 singly-occupied orbitals for actinide and lanthanide dimers, and thus providing for a technique to enumerate $$\upomega {{-}} \upomega $$ states arising from both very high spin open-shell states as well as low spin states exhaustively.

Three new alkyl chain substituted complexes [Fe(H2Bpz2)2(Cn-bipy)] (pz = pyrazolyl, Cn-bipy = bipyridine alkyl chain diester, n = 3 (3), 4 (4) and 5 (5)) show versatile spin state switching behaviour with different “tail” lengths as revealed by structural and magnetic analyses. The most striking phenomenon is observed for 5 which undergoes an abrupt spin transition accompanied by thermal hysteresis of ca. 10 K, which is attributed to crystal packing effects derived from the competition between π⋯π and C–H⋯O interactions. Interestingly, each of the complexes exhibits similar gradual and complete spin crossover in methanol solution with a transition temperature around 249 K, as deduced from temperature-dependent UV-vis spectroscopy. This highlights the differences between the solid state (ligand field; crystal packing) and solution (ligand field; solvation) effects on spin crossover. This work demonstrates that the length of the complex's alkyl chain substituents on the complex can have a large impact on the transition temperature and profile of solid state spin crossover, offering a potential path to the fabrication of soft matter spin crossover materials.

The spin states of three earlier described cobalt(II) clathrochelates as films on the quartz supports are studied for the first time. The magnetochemical study shows that the temperature-induced spin transition observed previously in the crystalline samples is retained in the films, which makes it possible to consider this class of coordination compounds with high chemical and thermal stability as promising components for molecular spintronic devices.

Controlling the spin states of freedom represents a significant challenge for the next-generation optoelectronic and spintronic devices. Chiral metal-halide semiconductors (MHS) have recently emerged as an important class of materials for spin-dependent photonic and electronic applications. In this Minireview, we first discussed the chemical and structural diversity of chiral MHS, highlighting the chirality formation mechanism. We then provided our current understanding on the spin-sensitive photophysical and transport process with a focus on how chirality enables the spin selectivity in chiral MHS. We summarized recent progress on the experimental demonstration of spin control in various photonic and spintronic devices. Finally, we discussed ongoing challenges and opportunities associated with chiral MHS.

Construction of metal–organic polyhedral clusters is promising and challenging in science due to their highly symmetric structures and potential application to molecular devices. In this work, three neutral nanocages of {[Fe(Tp)(CN)3]24[M(H2O)2]6[M(L)(H2O)]12}·xH2O (1-Fe, 2-Ni, and 3-Mn for M = Fe, Ni, Mn and x = 6, 2, 4, respectively; Tp = hydrotris(pyrazolyl)borate and L = pyridine-4-carboxylate) were prepared through the assembly of [Fe(Tp)(CN)3]− with FeII, NiII, or MnII ions and pyridine-4-carboxaldehyde, which was oxidized to pyridine-4-carboxylic acid during the reactions. Single crystal structure analyses revealed that each cage has the same core structure of an Archimedean polyhedra, the pseudo-rhombicuboctahedron. Elemental analyses and magnetic and spectroscopic measurements were performed to determine the oxidation and spin states of the composite metal ions, demonstrating that their electron configurations can be altered by changing the metal ions and deprotonating the auxiliary ligands. In addition, magnetic studies indicated that the metal ions were ferromagnetically coupled within the cage structure. These clusters exhibited magnetocaloric effects (MCEs) with the entropy changes of 11.55 J kg−1 K−1 for 1-Fe, 5.84 J kg−1 K−1 for 2-Ni, and 19.84 J kg−1 K−1 for 3-Mn at 3 K and 8.5 T, and 3-Mn is among the family of high-performance 3d-metal-based magnetic coolants.

The synthesis of six 2,6-di(pyrazol-1-yl)pyridine derivatives bearing dithiolane or carboxylic acid tether groups is described: [2,6-di(pyrazol-1-yl)pyrid-4-yl]methyl (R)-lipoate (L1), 2-[(2,6-di(pyrazol-1-yl)pyridine)-4-carboxamido]ethyl (R)-lipoate (L2), 2-[(2,6-di(pyrazol-1-yl)pyridine)-4-carboxy]ethyl (R)-lipoate (L3), N-([2,6-di(pyrazol-1-yl)pyrid-4-ylsulfanyl]-2-aminoethyl (R)-lipoamide (L4), 2-[(2,6-di(pyrazol-1-yl)pyridine)-4-carboxamido]acetic acid (L5) and 2-[(2,6-di(pyrazol-1-yl)pyridine)-4-carboxamido]propionic acid (L6). The iron(ii) perchlorate complexes of all the new ligands exhibit gradual thermal spin-crossover (SCO) in the solid state above room temperature, except L4 whose complex remains predominantly high-spin. Crystalline [Fe(L6)2][ClO4]2·2MeCN contains three unique cation sites which alternate within hydrogen-bonded chains, and undergo gradual SCO at different temperatures upon warming. The SCO midpoint temperature (T1/2) of the complexes in CD3CN solution ranges between 208-274 K, depending on the functional group linking the tether groups to the pyridyl ring. This could be useful for predicting how these complexes might behave when deposited on gold or silica surfaces.

Spin crossover in iron(II) and iron(III) complexes continues to receive much attention for the construction of molecular devices due to the presence of functionalities arising from their spin state switching behavior. Notably, some such compounds are associated with a light-induced excited spin-state trapping (LIESST) effect, which is responsible for the optical switching of their spin states. However, as opposed to iron(II) complexes, reports of iron(III) complexes that exhibit a LIESST effect are somewhat limited. This review presents an overview of the reported examples of SCO iron(III) systems that display LIESST effects.

Influence of the chemical pressure (x) in single crystals of FexMn1 – xS (0.12 ≤ x ≤ 0.29) on the spin state of iron ions was studied by Mossbauer spectroscopy in the temperature range from 4.2 to 300 K. Peculiarities of formation of the paramagnetic and antiferromagnetic phases of solid solutions were found. Substitution of Fe2+ cations in the high-spin state for Mn2+ was found to occur in FexMn1 – xS as x changes. A decrease in the distance between the ions in FexMn1 – xS induces changes in the state of the Fe2+ ions in the samples with x = 0.25 and 0.29. The asymmetry parameter of the electric field gradient (EFG) tensor and the angle between the directions of the magnetic moment and the principal axis of the electric field gradient were found to change in the magnetically ordered phase at 4.2 K; the angle between the magnetic moment and the electric field gradient axis changes from 21° in the sample with x = 0.12 to 33° when x = 0.29.

Here we report a surface morphology-induced spin state control in ultrathin films of a spin-crossover (SCO) material. The surface microstructure of film domains exhibited selectivity, to stabilize the SCO-active high-spin (HS) or SCO-inactive high-spin (HS2) states. To date, the latter has only been confirmed in the bulk counterpart at gigapascal pressure.

Examination of the stable (110) surface of γ-alumina reveals that there are three different types of sites available to host a single Fe atom. With the carefully calibrated density functional approach (M12-L/SV), three types of Fe single sites on the (110) surface of γ-alumina have been investigated under the periodic boundary conditions. The most stable Fe replacement site on the (110) surface of γ-alumina has been found to be represented by the tri-coordinated FeI position with the quartet spin state. The replacement of Al by Fe atoms at the Al site leads to charge redistributions of the neighboring O atoms. However, sublayer charge distribution is less affected. A significant contribution of p orbitals of the O atoms in the surface phase to the LUMO has been found for the tri-coordinated FeI substitution on the (110) surface. The corresponding oxygen atoms (OA and OA1) have been activated due to the existence of FeI in their neighborhood. The loosened neighboring AlIII–OA bonds match this activation. This activation of O suggests the existence of an important source of the reactive O during the Fe catalytic oxidation of CO processes.

Organic radicals are an emerging class of luminophores possessing multiplet spin states and potentially showing spin-luminescence correlated properties. We investigated the mechanism of recently reported magnetic field sensitivity in the emission of a photostable luminescent radical, (3,5-dichloro-4-pyridyl)bis(2,4,6-trichlorophenyl)methyl radical (PyBTM) doped into host αH-PyBTM molecular crystals. The magnetic field (0–14 T), temperature (4.2–20 K), and the doping concentration (0.1, 4, 10, and 22 wt%) dependence on the time-resolved emission were examined by measuring emission decays of the monomer and excimer. Quantum mechanical simulations on the decay curves disclosed the role of the magnetic field; it dominantly affects the spin sublevel population of radical dimers in the ground states. This situation is distinctly different from that in conventional closed-shell luminophores, where the magnetic field modulates their excited-state spin multiplicity. Namely, the spin degree of freedom of ground-state open-shell molecules is a new key for achieving magnetic-field-controlled molecular photofunctions., We investigated the mechanism of the magnetic field effect (MFE) on the emission of a luminescent radical doped into host crystals. It was revealed that the spin sublevel population of radical dimers in the ground states is the key that governs the MFE.

High entropy oxides (HEOs) are single phase solid solutions consisting of five or more elements in equiatomic or near-equiatomic proportions incorporated into the cationic sub-lattice(s). The uniqueness of the HEOs lies in their extreme chemical complexity enveloped in a single crystallographic structure, which in many cases results in novel functionalities. From the local structure perspective, HEOs consist of an unusually large number of different metal–oxygen–metal couples. Consequently, magnetic correlations in HEOs that inherently depend on the coordination geometry, valence, spin state and type of the metal cations that are hybridized with the bridging oxygen, are naturally affected by an extreme diversity of neighboring ionic configurations. In these conditions, a complex magneto-electronic free-energy landscape in HEOs can be expected, potentially leading to stabilization of unconventional spin-electronic states. This Frontier article provides an overview of the unique magnetic features stemming from the extreme chemical disorder in HEOs along with the possible opportunities for further research and exploration of potential functionalities.

Paramagnetic single-molecule magnets (SMMs) interacting with the ferromagnetic electrodes of a magnetic tunnel junction (MTJ) produce a new system. The properties and future scope of new systems differ dramatically from the properties of isolated molecules and ferromagnets. However, it is unknown how far deep in the ferromagnetic electrode the impact of the paramagnetic molecule and ferromagnet interactions can travel for various levels of molecular spin states. Our prior experimental studies showed two types of paramagnetic SMMs, the hexanuclear Mn6 and octanuclear Fe–Ni molecular complexes, covalently bonded to ferromagnets produced unprecedented strong antiferromagnetic coupling between two ferromagnets at room temperature leading to a number of intriguing observations (P. Tyagi, et al., Org. Electron., 2019, 64, 188–194. P. Tyagi, et al., RSC Adv., 2020, 10, (22), 13006–13015). This paper reports a Monte Carlo Simulations (MCS) study focusing on the impact of the molecular spin state on a cross junction shaped MTJ based molecular spintronics device (MTJMSD). Our MCS study focused on the Heisenberg model of MTJMSD and investigated the impact of various molecular coupling strengths, thermal energy, and molecular spin states. To gauge the impact of the molecular spin state on the region of ferromagnetic electrodes, we examined the spatial distribution of molecule-ferromagnet correlated phases. Our MCS study shows that under a strong coupling regime, the molecular spin state should be ∼30% of the ferromagnetic electrode's atomic spins to create long-range correlated phases.

A low spin state and diamagnetic CoIII complex 1 possessing pyrrolopyrrolizine ligands formed with dicyanovinylene-bis-(meso-aryl)dipyrrin was synthesized via the thermally activated metalation with CoCl2 and isolated via column chromatography. The nuclear magnetic resonance of complex 1 revealed diamagnetism, thereby confirming the structure of the octahedral CoIII-complex of strong-field ligands. The resulting molecular structure of 1 was elucidated by the X-ray diffraction analysis. An arrangement of two pyrrolizine-ligands for the metal chelation was found in the AB–BA order, which was distinct from the case observed during the formation of bis-NiII-expanded porphyrinoids.

In this work, we present a spin-crossover (SCO) complex molecular formulation [Fe(Ln)2](BF4)2 in an electrochemical single couple solution. A Seebeck voltage arises when an electrochemical single couple solution is subjected to a temperature difference, resulting in a single couple reaction at either terminal of the electrochemical cell. The ultrahigh Seebeck coefficients were obtained due to a number of molecular optimisation strategies. The [Fe(L16)2](BF4)2 complex demonstrated a maximum Seebeck coefficient of 8.67 mV K−1, achieved through a six-pronged approach to maximise entropy during the transition from low spin (LS) to high spin (HS) through: (i) a change in spin state, (ii) a change in physical liquid crystalline state, (iii) the spin Seebeck effect, (iv) the kosmotropic and chaotropic effect, (v) the fastener effect and (vi) thermal heat absorbance. A reduction of the Seebeck coefficient to 1.68 mV K−1 during the HS–LS transition at higher temperatures is related to the single spin state transition entropy change. In summary, this paper presents a systematic study to identify the contributing factors in the production of a sensor with an ultrahigh Seebeck coefficient for energy harvesting through the optimisation of its molecular entropy elements.

We benchmark the accuracy of quantum-chemical methods, including wave function theory methods [coupled cluster theory at the CCSD(T) level, multiconfigurational perturbation-theory (CASPT2, NEVPT2) and internally contracted multireference configuration interaction (MRCI)] and 30 density functional theory (DFT) approximations, in reproducing the spin-state splittings of metallocenes. The reference values of the electronic energy differences are derived from the experimental spin-crossover enthalpy for manganocene and the spectral data of singlet-triplet transitions for ruthenocene, ferrocene, and cobaltocenium. For ferrocene and cobaltocenium we revise the previous experimental interpretations regarding the lowest triplet energy; our argument is based on the comparison with the lowest singlet excitation energy and herein reported, carefully determined absorption spectrum of ferrocene. When deriving vertical energies from the experimental band maxima, we go beyond the routine vertical energy approximation by introducing vibronic corrections based on simulated vibrational envelopes. The benchmarking result confirms the high accuracy of the CCSD(T) method (in particular, for UCCSD(T) based on Hartree-Fock orbitals we find for our dataset: maximum error 0.12 eV, weighted mean absolute error 0.07 eV, weighted mean signed error 0.01 eV). The high accuracy of the single-reference method is corroborated by the analysis of a multiconfigurational character of the complete active space wave function for the triplet state of ferrocene. On the DFT side, our results confirm the non-universality problem with approximate functionals. The present study is an important step toward establishing an extensive and representative benchmark set of experiment-derived spin-state energetics for transition metal complexes.

Nickel transition-metal catalysts are important materials which are widely used in (de)hydrogenation reactions. Typical NiII catalysts adopt a square planar geometry and a low-spin state owing to their d8 electronic configuration. Here, we describe a mechanistic investigation of a novel octahedral NiII catalyst with a paramagnetic nature catalysing the α-alkylation of amides. Both non-bifunctional and bifunctional pathways were considered. In addition, we clarified the superiority of the high-spin state by comparing the geometries, valence electronic configurations, and rate-limiting energy barriers of the high- and low-spin states. Our results indicate that the novel octahedral nickel catalyst favours the bifunctional pathway and tends to maintain a high-spin state throughout the reaction due to the N-arm ligand. This computational study suggests that the spin state has the potential to influence the catalyst structure and reaction mechanism. Furthermore, these findings present novel insights for the design of NiII catalysts with high-spin states.

Cobalt oxyhydroxide (CoOOH) has attracted great attention in electrochemical water splitting. However, the mechanism behind its catalytic performance and how to improve its activity are still under debate. In the work, we propose that strain engineering is an effective and simple way to achieve the purpose. Based on density functional theory (DFT), we investigate the effects of strain engineering on the electronic structure and catalytic performance of two-dimensional (2D) CoOOH and the underlying mechanism of the oxygen evolution reaction (OER). We find that strain engineering is effective to tailor the electronic configuration of Co3+ ions in CoOOH, which can be transferred from low spin (LS: t62ge0g) to high spin (HS: t42ge2g) at a tension of 9%. Importantly, we show that LS CoOOH is a poor OER catalyst, because it is ineffective for O2 release with a large energy (1.35 eV). However, HS CoOOH is much more active in the OER because of smaller O2 release energy (0.03 eV) and more effective O–O bond coupling (1.21 eV) in the intramolecular oxygen coupling mechanism. The overpotential for LS CoOOH is 0.66 V according to the hydroxide ion attack mechanism, while the direct intramolecular coupling is hard to occur. HS CoOOH shows low overpotentials, 0.32 and 0.5 V, for the intramolecular coupling and hydroxide ion attack, respectively, which are comparable to those of the best OER catalysts (0.25 to 0.4 V). Our work demonstrates that the spin state transition of Co3+ ions tuned by strain engineering is an effective way to improve the OER activity of 2D CoOOH.

Half-metallic ferromagnetic materials have attracted a lot of attention due to their probable technological applications in spintronics. In this respect, doping plays a crucial role in tailoring or controlling the physical properties of the system. Herein, the impact of both hole and electron doping on the structural, electronic and magnetic properties of the recent high pressure synthesized non-magnetic insulator Ba2CaMoO6 double perovskite oxide are investigated by replacing one of the Mo ions with Nb and Tc. The structural and mechanical stability of the undoped/doped materials are analyzed by calculating the formation energies and stiffness tensors, respectively, which confirm the system's stability. Interestingly, our results revealed that Nb- and Tc-doped systems display an electronic transition from insulating to p- and n-type half-metallic ferromagnetic states, respectively. The most striking feature of the present study is that oxygen ions become spin-polarized, with a magnetic moment of ∼0.12 μB per atom, and are mainly responsible for conductivity in the Nb-doped system. However, the admixture of Tc 4d non-degenerate orbitals are primarily contributing to the metallicity in the Tc-doped structure, with a moment of ∼0.59 μB. It is also found that Nb and Tc ions remain in the 5+ and 7+ states with electronic configurations of t22g↑t22g↓e0g↑e0g↓ and t32g↑t22g↓e0g↑e0g↓, with spin states of S = 0 and S = 1/2 in the individual doped systems, respectively. Hence, the present work proposes that a doping strategy with a suitable candidate could be beneficial to tune the physical properties of the materials for their potential utilization in advanced spin-based devices.

Singlet fission duplicates triplet excitons for improving light harvesting efficiency. The presence of the interaction between electronic and nuclear degrees of freedom complicates the interpretation of correlated triplet pairs. We report a quantum chemistry study on the significance and subtleties of multistate and multimode pathways in forming triplet pair states of the pentacene dimer through a six-state vibronic-coupling Hamiltonian derived from many-electron adiabatic wavefunctions of an ab initio density matrix renormalization group. The resulting spin values of the singlet manifolds on each pentacene center are computed, and the varying spin nature can be distinguished clearly with respect to dimer stacking and vibronic progression. Our monomer spin assignments reveal the coexistence of both lower-lying weak and higher-lying strong charge transfer states which interact vibronically with the triplet pair state, providing important implications for its generation and separation occurring in vibronic regions. This work conveys the importance of the many-electron process requiring close low-lying singlet manifolds to determine the subtle fission details, and represents an important step for understanding vibronically resolved spin states and conversions underlying efficient singlet fission., Singlet fission in pentacene necessitates the vibronic progression of weak and strong charge-transfer states with correlated triplet pairs.

Heterostructures composed of dissimilar oxides with different properties offer opportunities to develop emergent devices with desired functionalities. A key feature of oxide heterostructures is interface electronics and orbital reconstructions. Here, we combined infinite-layered SrCuO2 and perovskite SrRuO3 into heterostructures. A rare high spin state as large as 3.0 μB f.u-1 and an increase in Curie temperature by 12 K are achieved in an ultrathin SrRuO3 film capped by a SrCuO2 layer. Atomic-scale lattice imaging shows the uniform CuO2-plane-to-RuO5-pyramid connection at the interface, where the regularly arranged RuO5 pyramids were elongated along the out-of-plane direction. As revealed by theoretical calculations and spectral analysis, these features finally result in an abnormally high spin state of the interfacial Ru ions with highly polarized eg orbitals. The present work demonstrates that oxygen coordination engineering at the infinite-layer/perovskite oxide interface is a promising approach towards advanced oxide electronics.

Self-assembly and characterisation of a supramolecular trigonal bipyramidal iron cage containing an [FeIII(μ2-F)6(FeII)3]3+ star motif at its core is reported. The complex can be formed in a one step reaction using an heterotopic ligand that supports site-specific incorporation of iron in three distinct electronic configurations: low-spin FeII, high-spin FeII and high-spin FeIII, with iron(II) tetrafluoroborate as the source of the bridging fluorides. Formation of a μ2-F bridged mixed-valence FeII-FeIII star is unprecedented. The peripheral high-spin FeII centres of the mixed-valence tetranuclear star incorporated in the iron cage are highly anisotropic and engage in F-mediated antiferromagnetic exchange with the central FeIII ion.

Detailed experimental and comprehensive theoretical analysis of singlet–triplet conversion in molecular hydrogen dissolved in a solution together with organometallic complexes used in experiments with parahydrogen (the H2 molecule in its nuclear singlet spin state) is reported. We demonstrate that this conversion, which gives rise to formation of orthohydrogen (the H2 molecule in its nuclear triplet spin state), is a remarkably efficient process that strongly reduces the resulting NMR (nuclear magnetic resonance) signal enhancement, here of 15N nuclei polarized at high fields using suitable NMR pulse sequences. We make use of a simple improvement of traditional pulse sequences, utilizing a single pulse on the proton channel that gives rise to an additional strong increase of the signal. Furthermore, analysis of the enhancement as a function of the pulse length allows one to estimate the actual population of the spin states of H2. We are also able to demonstrate that the spin conversion process in H2 is strongly affected by the concentration of 15N nuclei. This observation allows us to explain the dependence of the 15N signal enhancement on the abundance of 15N isotopes.

The synthesis of quality single crystals is central to materials chemistry for optical, magnetic, and electronic device applications. The present work reports on the synthesis of single crystals of iron-triazole coordination polymer [Fe(Htrz)2(trz)](BF4) where (Htrz) = 1H-1,2,4-triazole. Crystals of size as long as 80 μm can be achived by controlling the temperature, precursor concentration, and solvent type. It is found that its thermal spin crossover depends largely on the crystal size. Fine crystals are ideal for depositing a thin film that exhibits redox activity. The largest crystals allow reliable electrical conductance measurements that reveal two different activation energies at the low spin state and the high spin state, which are one order of magnitude smaller than the electronic gaps calculated based on density functional theory. The synthetic route sought in the present study can be applied to other coordination polymers and related materials and provides the basis for their applications.

Three iron(II) complexes, [Fe(L1)2(NCS)2(MeOH)2] (1), [Fe(L1)2(NCSe)2(MeOH)2] (2), and [Fe(L2)2(NCS)2]n (3) (L1 = 2,5-dipyridyl-3,4-ethylenedioxythiophene and L2 = 2,5-diethynylpyridinyl-3,4-ethylenedioxythiophene), have been synthesized using redox-active luminescent ethylenedioxythiophene (EDOT)-based ligands, and characterized by variable temperature single-crystal X-ray diffraction, (photo)magnetic, optical reflectivity, and spectroscopy studies. Magneto-structural investigations revealed that 1 and 2 are mononuclear with a FeN4O2 octahedral coordination geometry and remain in a high-spin (HS) (S = 2) state in a temperature range of 2–280 K. Interestingly, a 2D coordination network structure with FeN6 surrounding each iron center was observed for 3, which exhibits reversible thermo-induced spin-state switching between the paramagnetic high-spin (HS) (S = 2) and diamagnetic low-spin (LS) (S = 0) states at around 105 K (T1/2). Furthermore, optical reflectivity and photomagnetic measurements at low temperature confirmed that 3 shows reversible ON/OFF switching between the photoinduced excited paramagnetic HS metastable state and diamagnetic LS state under light irradiation (ON mode using red light and OFF mode using green light). Finally, the photoinduced excited HS state can be reversibly relaxed back to the diamagnetic ground LS state by heating the system at ca. 88 K (TLIESST = 88 K) (light-induced excited spin state trapping (LIESST) effect). Furthermore, 3 also showed an exciting and unique 18 K wide light-induced thermal hysteresis (LITH) effect above liquid nitrogen temperature (100 K). DFT and CASSCF level theoretical calculations were utilized to better understand the magneto-structural correlations of these complexes.

Controlling the energetics of spin crossover (SCO) in Fe(II)-polypyridine complexes is critical for designing new multifunctional materials or tuning the excited-state lifetimes of iron-based photosensitizers. It is well established that the Fe–N “breathing” mode is important for intersystem crossing from the singlet to the quintet state, but this does not preclude other, less obvious, structural distortions from affecting SCO. Previous work has shown that halogenation at the 6 and 6′′ positions of tpy (tpy = 2,2′;6′,2′′-terpyridine) in [Fe(tpy)2]2+ dramatically increased the lifetime of the excited MLCT state and also had a large impact on the ground state spin-state energetics. To gain insight into the origins of these effects, we used density functional theory calculations to explore how halogenation impacts spin-state energetics and molecular structure in this system. Based on previous work we focused on the ligand “rocking” motion associated with SCO in [Fe(tpy)2]2+ by constructing one-dimensional potential energy surfaces (PESs) along the tpy rocking angle for various spin states. It was found that halogenation has a clear and predictable impact on ligand rocking and spin-state energetics. The rocking is correlated to numerous other geometrical distortions, all of which likely affect the reorganization energies for spin-state changes. We have quantified trends in reorganization energy and also driving force for various spin-state changes and used them to interpret the experimentally measured excited-state lifetimes.

The study of various oxidation states of chromium with Sargassum sp. is of particular interest since hexavalent chromium is reduced to trivalent chromium in an aqueous solution. In this study, a systematic density functional theory (DFT) calculations were performed to study the interactions of transition metal chromium ion with different oxidation states and spin states with the Sargassum sp. decorated with carboxylate (acetate) at the wB97XD/6-311++ G(d,p) level of theory. The structures and binding energies of chromium metal-carboxylate complexes at various oxidation states and spin states in gas phase were examined. The coordination strength of Cr(VI) with the acetate ligand was predominantly the strongest compared to the other oxidation states. Vibrational frequency analysis, for the homoleptic monomers of tris [CrIII(AC)3]0 and [CrVI(AC)3]3+ complexes, illustrate good harmony with the experimental and theoretical calculated frequencies. Using the time-dependent DFT (TD-DFT) at the level of CAM-B3LYP/6-311++G(d,p), the vertical excitation energies were obtained. The stabilization energies derived using the second order perturbation theory, Eij(2), of NBO analysis confirmed the greater charge transfer for the observed trends in the metal binding. The calculated binding energies (ΔE) and interactions energies SEij(2) favor the formation of [CrVI(AC)3]3+ complexes. The findings of this study identify efficient electronic factors as major contributors to the metal binding affinities, with promising possibilities for the design of metal-ligand complexes and sensing of the metal ions.

Supramolecular tessellation represents a newly emerging powerful tool for constructing crystalline and quasicrystalline structural aesthetics with molecular polygons/planigons. In turn, expanding such 2-periodic tessellation as tectonic layer to 3-periodic architecture of frameworks, promises the sublimation from visual beauty for pure appreciation to sophisticated performance of porous materials for real application, enabling us to build macroscopic behavior at the molecular scale. With the above foresight, we introduce herein a new discovery that integrating supramolecular tessellation and pillared-layer strategy assembles supramolecular frameworks (SFs). The tectonic layers are based on rhombille tessellation of hydrogen-bondings between FeII molecular building blocks and interstitial water molecules, showing a rare kagome dual (kgd) net. Under this strategy, we first observed that a new zlg 3D topology was born by pillaring with kgd layer. These SFs offer potential channel/voids for guests’ respiration, inducing a reversible allosteric transformation from ligand substitution. The transformation alters significantly the spin state which was quantified by 57Fe Mossbauer spectroscopy, NMR, magnetic dilution and DFT calculations. These compounds show magnetic and chromatic bistability (see TOC), providing a broad scope towards multifuctional frameworks via multifarious supramolecular tessellation.