Ab initio investigation of the geometrical behavior in solution and electronic structure of the anion complexes [bis(1,3-dithiole-2-thione-4,5-dithiolate)M], for M = Bi(III), Sb(III), and Zn(II)

CONTEXT

1,3-Dithiole-2-thione-4,5-dithiolate (dmit) ligands are known for their conductive and optical properties. Dmit compounds have been assessed for use in sensor devices, information storage, spintronics, and optical material applications. Associations with various metallic centers endow dmit complexes with magnetic, optical, conductive, and antioxidant properties. Optical doping can facilitate the fabrication of magnetic conductor materials from ground-state nonmagnetic cations. While most studied complexes involve transition-metal centers due to their diverse chemistry, compounds with representative elements are less explored in the literature. This study investigated the structural and electronic properties of bisdmit complexes with representative Bi(III), Sb(III), and Zn(II) cations. AIMD calculations revealed two new geometries for Bi(III) and Zn(II) complexes, diverging from the isolated geometry typically used in quantum chemical calculations. The coordination of acetonitrile molecules to the cationic centers of the complexes resulted in unstable structures, while the dimerization of the complexes was stable. SA-CASSCF/NEVPT2 calculations were applied to the structures of the isolated complexes and stable dimers, confirming the multireference character of the electronic structure of the three systems and the multiconfigurational character of the Bi(III) complex. The electronic spectra simulated by the STEOM-DLPNO-CCSD calculations accurately reproduced the experimental UV‒Vis spectra indicating the participation of the isolated Bi(III) dmit complex and its dimeric form in solution.

METHODOLOGY

AIMD calculations of the dmit salts were conducted using the GFN2-xTB method with 60 explicit acetonitrile molecules as the solvent at 300 K for a total simulation time of 50.0 ps, with printing intervals of 0.5 fs. The final geometries were optimized employing the PBEh-3c compound method, incorporating implicit conductor-like polarizable continuum model (CPCM) solvation for acetonitrile. Local energy decomposition (LED) analysis at the DLPNO-CCSD(T)/Def2-TZVP level of theory was utilized to investigate the stability of the complex geometries identified by AIMD. The electronic structures of the complexes were assessed using the SA-CASSCF/NEVPT2/Def2-TZVP method to confirm the multiconfigurational and multireference nature of their electronic structures. Electronic spectra were analyzed using the STEOM-DLPNO-CCSD/Def2-TZVP method, with CPCM used to simulate an acetonitrile medium.

Step-by-Step Electrocrystallization Processes to Make Multiblock Magnetic Molecular Heterostructures

Assembling conductive or magnetic heterostructures by bulk inorganic materials is important for making functional electronic or spintronic devices, such as semiconductive p-doped and n-doped silicon for P-N junction diodes, alternating ferromagnetic and nonmagnetic conductive layers used in giant magnetoresistance (GMR). Nonetheless, there have been few demonstrations of conductive or magnetic heterostructures made by discrete molecules. It is of fundamental interest to prepare and investigate heterostructures based on molecular conductors or molecular magnets, such as single-molecule magnets (SMMs). Herein, we demonstrate the fabrication of a series of molecular heterostructures composed of (TTF)₂M(pdms)₂ (TTF = tetrathiafulvalene, M = Co(II), Zn(II), Ni(II), H₂pdms = 1,2-bis(methanesulfonamido)benzene) multiple building blocks through a well-controlled step-by-step electrocrystallization growth process, where the Co(pdms)₂, Ni(pdms)₂, and Zn(pdms)₂ anionic complex is a SMM, paramagnetic, and diamagnetic molecule, respectively. Magnetic and SMM properties of the heterostructures were characterized and compared to the parentage (TTF)₂Co(pdms)₂ complex. This study presents the first methodology for creating molecule-based magnetic heterostructural systems by electrocrystallization.

Proton-electron-coupled functionalities of conductivity, magnetism, and optical properties in molecular crystals

Proton-electron-coupled reactions, specifically proton-coupled electron transfer (PCET), in biological and chemical processes have been extensively investigated for use in a wide variety of applications, including energy conversion and storage. However, the exploration of the functionalities of the conductivity, magnetism, and dielectrics by proton-electron coupling in molecular materials is challenging. Dynamic and static proton-electron-coupled functionalities are to be expected. This feature article highlights the recent progress in the development of functionalities of dynamic proton-electron coupling in molecular materials. Herein, single-unit conductivity by self-doping, quantum spin liquid state coupled with quantum fluctuation of protons, switching of conductivity and magnetism triggered by the disorder-order transition of deuterons, and their external responses under pressure and in the presence of an electric field are introduced. In addition, as for the functionalities of proton-d/π-electron coupling in metal dithiolene complexes, magnetic switching with multiple PCET and vapochromism induced by electron transfer through hydrogen-bond (H-bond) formation is introduced experimentally and theoretically. We also outlined the basic and applied issues and potential challenges for development of proton-electron-coupled molecular materials, functionalities, and devices.

Synthesis, Crystal Structures and Magnetic Properties of Trinuclear {Ni2Ln} (LnIII = Dy, Ho) and {Ni2Y} Complexes with Schiff Base Ligands

The reaction of the Schiff base ligand o-OH-C6H4-CH=N-C(CH2OH)3, H4L, with Ni(O2CMe)2∙4H2O and lanthanide nitrate salts in a 4:2:1 ratio lead to the formation of the trinuclear complexes [Ni2Ln(H3L)4(O2CMe)2](NO3) (Ln = Dy (1), Ho (2), and Y (3)) which crystallize in the non-centrosymmetric space group Pna21. The complex cation consists of the three metal ions in an almost linear arrangement. The {Ni2Ln} moieties are bridged through two deprotonated Ophenolato groups from two different ligands. Each terminal NiII ion is bound to two ligands through their Ophenolato, the Nimino atoms and one of the protonated Oalkoxo groups in a distorted octahedral. The central lanthanide ion is coordinated to four Ophenolato oxygen from the four ligands, and four Ocarboxylato atoms from two acetates which are bound in the bidentate chelate mode, and the coordination polyhedron is biaugmented trigonal prism, which probably results in a non-centrosymmetric arrangement of the complexes in the lattice. The magnetic properties of 1–3 were studied and showed that 1 exhibits field induced slow magnetic relaxation.

Tunable magnetic anisotropy in luminescent cyanido-bridged {Dy2Pt3} molecules incorporating heteroligand PtIV linkers

The interest in the generation of photoluminescence in lanthanide(III) single-molecule magnets (SMMs) is driven by valuable magneto-optical correlations as well as perspectives toward magnetic switching of emission and opto-magnetic devices linking SMMs with optical thermometry. In the pursuit of enhanced magnetic anisotropy and optical features, the key role is played by suitable ligands attached to the 4f metal ion. In this context, cyanido complexes of d-block metal ions, serving as expanded metalloligands, are promising. We report two novel discrete coordination systems serving as emissive SMMs, {[Dy^III(H₂O)₃(tmpo)₃]₂[Pt^IVBr₂(CN)₄]₃}·2H₂O (1) and {[Dy^III(H₂O)(tmpo)₄]₂[Pt^IVBr₂(CN)₄]₃}·2CH₃CN (2) (tmpo = trimethylphosphine oxide), obtained by combining Dy^III complexes with uncommon dibromotetracyanidoplatinate(IV) ions, [Pt^IVBr₂(CN)₄]^2-. They are built of analogous Z-shaped cyanido-bridged {Dy₂Pt₃} molecules but differ in the coordination number of Dy^III (C.N. = 8 in 1, C.N. = 7 in 2) and the number of coordinated tmpo ligands (three in 1, four in 2) which is related to the applied solvents. As a result, both compounds reveal Dy^III-centred slow magnetic relaxation but only 1 shows SMM character at zero dc field, while 2 is a field-induced SMM. The relaxation dynamics in both systems is governed by the Raman relaxation mechanism. These effects were analysed using ac magnetic data and the results of the ab initio calculations with the support of magneto-optical correlations based on low-temperature high-resolution emission spectra. Our findings indicate that heteroligand halogeno-cyanido Pt^IV complexes are promising precursors for emissive SMMs with the further potential of sensitivity to external stimuli that may be related to the lability of the axially positioned halogeno ligands.

Self-Healing Metallacycle-Cored Supramolecular Polymers Based on a Metal-Salen Complex Constructed by Orthogonal Metal Coordination and Host-Guest Interaction with Amino Acid Sensing

A platinum(II) metallacycle-cored supramolecular network based on a metal-salen complex was successfully constructed by two orthogonal noncovalent interactions (host-guest interactions and metal coordination interactions). The obtained metallo-supramolecular polymer could further form gels when the concentration of metallacycle 1 was 160.0 mM. This gel exhibited multiple stimuli-responsive gel-sol phase transitions under different stimuli, such as temperature, competitive guests, etc. Moreover, it exhibited good self-healing properties and could be used as a turn-off sensor for thiol-containing amino acids.

4f-π Molecular Hybrid Exhibiting Rich Conductive Phases and Slow Relaxation of Magnetization

Cooperation between single-molecule magnets and electrical conductivity holds promise for preparing high-density magnetic devices; however, there are only a few reports so far. Here we report a 4f-π-based molecular hybrid, k-(ET)₅Dy(NCS)₇(KCl)_0.5 (1) (ET = bis(ethylenedithio)tetrathiafulvalene, NCS^- = thiocyanate), which undergoes slow relaxation of the magnetization and electrical conductivity. Unlike common ET-based conductive salts, K⁺ ions were intercalated into ET layers and coordinated with ET radicals. We found that the ET charges were sensitive to temperature, resulting in rich conductive phases at 75-300 K. In particular, the upturn in conductivity with a clear hysteresis loop was explained by the formation of partially oxidized states with charges close to 0.5+, which accounts for a metallic state. From the results of electronic structure calculations, the hole concentration increased to 125 K, which is consistent with a partially oxidized state upon cooling. The weak antiferromagnetic interactions accompanied by a dual magnetic relaxation process below 4 K are closely associated with the weak 4f-π interactions.

Single Mn Atom Doping in Chiral Sensitive Assembled Gold Clusters to Molecular Magnet

Chiral stirred optical and magnetic properties, through the doping of assembled ultrasmall metal clusters (AMCs), are promising discernment to rivet the molecule-like quantum devices. Here, the single manganese (Mn) atom doping and assembly of the gold cluster (Au₈), leading to the chirality driven magnetism, has been achieved through a ligand-mediated growth. The X-ray absorption near edge structure and electron paramagnetic resonance studies corroborate the tetrahedral coordinated local structure of Mn dopant in the Au host. The optical and vibrational circular dichroic analysis affirms the modulation of chirality (negative to positive) in the presence of the Mn. A distinct ferromagnetic hysteresis loop at 300 K shows Mn ridden chiral sensitive ferromagnetism in contrary to the ligand influenced superparamagnetic undoped AMCs. The spin-polarized density functional theory level of calculations reveal the partial overlapping of spin-up and -down density of states in the doped AMCs, attributing to the ferromagnetic nature as like a molecular magnet suitable for the opto-spintronics application.

New Radical Cation Salts Based on BDH-TTP Donor: Two Stable Molecular Metals with a Magnetic [ReF6]2− Anion and a Semiconductor with a [ReO4]− Anion

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.

Emergence of Metallic Conduction and Cobalt(II)-Based Single-Molecule Magnetism in the Same Temperature Range

Single-molecule magnets exhibit magnetic bistabililties at the molecular level, making them promising for molecule-based spintronics due to high magnetic densities. The incorporation of SMM behavior and electrical conductivity in one compound is rare because these two physical properties often do not operate in the same temperature range, which further hinders their use in practical applications. Here we present an organic-inorganic molecular hybrid, β″-(BEDO-TTF)₃[Co(pdms)₂]·(MeCN)(H₂O)₂ (BO3) (BEDO-TTF = bis(ethylenedioxy)tetrathiafulvalene and H₂pdms = 1,2-bis(methanesulfonamido)benzene), which manifests both metallic conduction (electrical conductivity up to 1000 S cm^-1 at 12 K under 2.0 gigapascal pressure) and SMM behavior in the temperature range 12-26 K for the first time.

Pseudo-tetrahedral vs. pseudo-octahedral ErIII single molecule magnets and the disruptive role of coordinated TEMPO radical

Tetrahedral Er^III complexes are potential candidates for high-performance single molecule magnets (SMMs).

Simultaneous manifestation of metallic conductivity and single-molecule magnetism in a layered molecule-based compound

Single-molecule magnets (SMMs) show superparamagnetic behaviour below blocking temperature at the molecular scale, so they exhibit large magnetic density compared to the conventional magnets. Combining SMMs and molecular conductors in one compound will bring about new physical phenomena, however, the synergetic effects between them still remain unexplored. Here we present a layered molecule-based compound, β′′-(BEDO-TTF)₄ [Co(pdms)₂]·3H₂O (BO4), (BEDO-TTF (BO) and H₂pdms are bis(ethylenedioxy)tetrathiafulvalene and 1,2-bis(methanesulfonamido)benzene, respectively), which was synthesized by using an electrochemical approach and studied by using crystal X-ray diffraction. This compound simultaneously exhibited metallic conductivity and SMM behaviour up to 11 K for the first time. The highest electrical conductivity was 400–650 S cm⁻¹ at 6.5 K, which is the highest among those reported so far for conducting SMM materials. Furthermore, antiferromagnetic ordering occurred below 6.5 K, along with a decrease in conductivity, and the angle-independent negative magnetoresistance suggested an effective electron correlation between the conducting BO and Co(pdms)₂ SMM layers (d–π interactions). The strong magnetic anisotropy and two-dimensional conducting plane play key roles in the low-temperature antiferromagnetic semiconducting state. BO4 is the first compound exhibiting antiferromagnetic ordering among SMMs mediated by π-electrons, demonstrating the synergetic effects between SMMs and molecular conductors.

A metallic single-molecule magnet was synthesised demonstrating simultaneous metallic conduction and excellent SMM properties at the same temperature range for the first time, with potential applications in molecule-based quantum spintronics.

Enhancing magnetic hardness by sonication assisted synthesis of heterometallic carbonato spin-glass Na[Ni(H2O)4Ru2(CO3)4]·3H2O

Control of magnetic performances of molecular magnets is essential but few efforts have been documented. A green and efficient sonication assisted synthesis of a new heterometallic diruthenium(ii,iii) carbonate, Na[Ni(H2O)4Ru2(CO3)4]·3H2O (1), was carried out by self-assembling in aqueous solution. Compound 1 exhibits spin-glass behavior below ∼5.0 K, and a systematic investigation of the ultrasonic irradiation influence on the powder samples reveals that their coercivity increases from 50 Oe to 743 Oe with the control of ultrasonic power under appropriate conditions.

Humidity-A Powerful Tool to Customize the Physical Properties of Molecular Magnets

Since the dawn of the century, people have been fascinated by the mysterious force that draws two pieces of lodestone (magnetite, Fe₃ O₄ ) to each other as well as by property of stilbite (natural zeolite, NaCa₄ [Si₂₇ Al₉ O₇₂ ]⋅28 H₂ O) to generate huge amounts of steam by rapidly heating the material. Nowadays, we know the first effect is addressed by magnetic attraction whereas the second one is related to the reversible sorption/desorption of water from humid air inside porous materials. For a long time, it was thought that these two, at first glance, were disjunctive properties that cannot be combined into one material. Nevertheless, the scientists have once again proved that there are no impossible things. Based on the discovery of the first molecular magnets, the idea to combine magnetic properties with other functionalities such as porosity gained great consideration by scientists from different research fields. Very soon, we witnessed numerous reports of novel multifunctional materials among which we can distinguish humidity-responsive magnets. In this manuscript, the most outstanding results for such systems working at normal temperature and pressure (NTP) will be presented to motivate in-depth research on this topic.

Dehydration-Hydration Switching of Single-Molecule Magnet Behavior and Visible Photoluminescence in a Cyanido-Bridged DyIIICoIII Framework

Microporous magnets compose a class of multifunctional molecule-based materials where desolvation-driven structural transformation leads to the switching of magnetic properties. Herein, we present a special type of microporous magnet where a dehydration-hydration process within a bimetal coordination framework results in the switching of emissive Dy^III single-molecule magnets (SMMs). We report a three-dimensional (3-D) cyanido-bridged coordination polymer, {[Dy^III(H₂O)₂][Co^III(CN)₆]}·2.2H₂O (1), and its dehydrated form of {Dy^III[Co^III(CN)₆]} (2), which was obtained through a reversible single-crystal-to-single-crystal transformation. Both phases are composed of paramagnetic Dy^III centers alternately arranged with diamagnetic hexacyanidocobaltates(III). The hydrated phase contains eight-coordinated [Dy^III(μ-NC)₆(H₂O)₂]^3- complexes of a square antiprism geometry, while the dehydrated form contains six-coordinated [Dy^III(μ-NC)₆]^3- moieties of a trigonal prism geometry. This change in coordination geometry results in the generation of Dy^III single-molecule magnets in 2, whereas slow magnetic relaxation effect is not observed for Dy^III sites in 1. The D_4d-to-D_3h symmetry change of Dy^III complexes produces also the shift of photoluminescent color from nearly white to deep yellow thanks to the modulation of emission bands of f-f electronic transitions. A combined approach utilizing dc magnetic data and low-temperature emission spectra confirmed an axial crystal field of trigonal prismatic Dy^III complexes in 2, which produces an Orbach type of slow magnetic relaxation. Therefore, we present a unique route to the efficient switching of SMM behavior and photoluminescence of Dy^III complexes embedded in a 3-D cyanido-bridged framework.

Humidity-Induced Switching between Two Magnetic and Structural Phases in a CoII -[WV (CN)8 ] Molecular Magnet

The self-assembly of cobalt(II) with purine and octacyanidotungstate(V) results in the formation of the three-dimensional Co₃ [W(CN)₈ ]₂ (purine)₂ ⋅8.5H₂ O (1) coordination polymer. This compound exhibits humidity-induced variation of the number of water molecules of crystallisation leading to a reversible structural phase transition and the alternation of the long-range ferromagnetic ordering temperature from T_C =29 K for the pristine assembly (1) to T_C =49 K for the sample stored in a low-humidity atmosphere (1-deh). This phenomenon can be attributed to a reversible change in the hydrogen-bonding network resulting in the modification of the local geometries of cobalt(II) as well as the cyanido bridges.

Ligand mixed-valence and electrical conductivity in coordination complexes containing a redox-active phenalenol-substituted ligand

A new redox-active hydrazone ligand bearing a phenalenol group is described (phpl), which produces neutral six-coordinate Fe and Co complexes (1 & 2) with the ligands identified in different oxidation states; an open-shell anion radical and closed-shell dianion. An intense and very low-energy intervalence charge transfer (IVCT) band is identified in solid-state and in solution in the complexes. Single crystals of 1 are semiconducting (at 300 K, σ = 3.05 × 10^-4 S cm^-1 with E_a = 245 meV).

Effect of coordination anion substitutions on relaxation dynamics of defect dicubane Zn2Dy2 tetranuclear clusters

We showcase the coordination anion substitution effect on the relaxation dynamics of defect dicubane Zn₂Dy₂ tetranuclear clusters.

Impact of fluoride for hydroxide substitution on the magnetic properties of a Co-based single-ion magnet imbedded in the barium apatite crystal lattice

The atomic group O–Co–O persists in the apatite channel and retains a high energy barrier for magnetization reversal.

Exploration of SMM behavior of Ln2 complexes derived from thianaphthene-2-carboxylic acid

Observations were made of field-induced SMM property of a dysprosium-based dinuclear complex derived from thianaphthene-2-carboxylic acid ligand.