Search Results (13)

Single crystals of pseudorotaxanes, [(FcCH₂NH₂CH₂Ar)(DB24C8)][PF₆] (DB24C8 = dibenzo[24]crown-8, Fc = Fe(C₅H₄)(C₅H₅), Ar = -C₆H₃-3,4-Cl₂, -C₆H₃-3,4-F₂, -C₆H₄-4-F, -C₆H₄-4-Cl, -C₆H₄-4-Br, -C₆H₃-3-F-4-Me, -C₆H₄-4-I) and [(FcCH₂NH₂CH₂C₆H₄-4-Me)(DB24C8)][Ni(dmit)₂] (dmit = 1,3-dithiole-2,4,5-dithiolate), were obtained from solutions containing DB24C8 and ferrocenylmethyl(arylmethyl)ammonium. X-ray crystallographic analyses of the pseudorotaxanes revealed that the aryl ring of the axle moiety and the catechol ring of the macrocyclic component were at close centroid distances and parallel or tilted orientation. The structures with parallel aromatic rings showed correlation of the distances between the centroids to Hammett substituent constants of the aryl groups. Full article

A molecular Mott insulator β′-EtMe₃Sb[Pd(dmit)₂]₂ is a quantum spin liquid candidate. In 2010, it was reported that thermal conductivity of β′-EtMe₃Sb[Pd(dmit)₂]₂ is characterized by its large value and gapless behavior (a finite temperature-linear term). In 2019, however, two other research groups reported opposite data (much smaller value and a vanishingly small temperature-linear term) and the discrepancy in the thermal conductivity measurement data emerges as a serious problem concerning the ground state of the quantum spin liquid. Recently, the cooling rate was proposed to be an origin of the discrepancy. We examined effects of the cooling rate on electrical resistivity, low-temperature crystal structure, and ¹³C-NMR measurements and could not find any significant cooling rate dependence. Full article

Colorimetric chemosensors are widely employed for in-field analysis to detect transition metal ions in real-time with the naked eye. Colorimetric chemosensors have attracted considerable attention because they can conveniently provide quantitative and qualitative information at a low cost. However, the development of colorimetric chemosensors for multiple-ion sensing where metal cations coexist has been limited. For this reason, we developed a new type of transition metal ion sensing material by selectively replacing functional groups on (diphosphine)Pt(dmit) molecules. The terminal groups of the diphosphine ligand were successfully substituted by the cyclohexyl groups, increasing the electron density of the thione moiety. Due to the electron donation ability of the cyclohexyl terminal groups, the proposed chemosensing material was able to selectively detect the mixture of Hg²⁺, Cu²⁺, and Ag⁺ in the presence of many types of interfering cations. To gain insight into the binding mechanisms between the metal ions and the developed (dchpe)Pt(dmit) molecule, density functional theory calculations were also performed. Full article

In this study, crystals of the hybrid layered structure, combined with Fe(III) Spin-Crossover (SCO) complexes with metal-dithiolate anionic radicals, and the precursors with nitrate and iodine counterions, are obtained and characterized. [Fe(III)(3-OMe-Sal₂trien)][Ni(dmit)₂] (1), [Fe(III)(3-OMe-Sal₂trien)]NO₃·H₂O (2), [Fe(III)(3-OMe-Sal₂trien)]I (3) (3-OMe-Sal₂trien = hexadentate N₄O₂ Schiff base is the product of the condensation of triethylenetetramine with 3-methoxysalicylaldehyde; H₂dmit = 2-thioxo-1,3-dithiole-4,5-dithiol). Bulk SCO transition was not achieved in the range 2.0–350 K for all three compounds. Alternatively, the hybrid system (1) exhibited irreversible segregation into the spatial fractions of Low-Spin (LS) and High-Spin (HS) phases of the ferric moiety, induced by thermal cycling. Fractioning was studied using both SQUID and EPR methods. Magnetic properties of the LS and HS phases were analyzed in the framework of cooperative interactions with anionic sublattice: Anion radical layers Ni(dmit)₂ (1), and H-bonded chains with NO₃ and I (2,3). LS phase of (1) exhibited unusual quasi-two-dimensional conductivity related to the Arrhenius mechanism in the anion radical layers, ρ_||c = 2 × 10⁵ Ohm·cm and ρ_⊥c = 7 × 10² Ohm·cm at 293 K. Ground spin state of the insulating HS phase was distinctive by ferromagnetically coupled spin pairs of HS Fe³⁺, S = 5/2, and metal-dithiolate radicals, S = 1/2. Full article

Hg²⁺ ions can accumulate in the natural environment and in organisms, where they cause damage to the central nervous system. Therefore, the detection of Hg²⁺ ions is essential for monitoring environmental contamination and human health. Herein, we demonstrate a simple method for tuning chemosensor signal ratios that significantly increased chemosensor selectivity for Hg²⁺ detection. Selectivity tuning was accomplished for chemosensors of the type (diphosphine)Pt(dmit), bearing the two different terminal groups 1,2-bis(diphenylphosphino)ethane (dppe) and 1,2-bis[bis(pentafluorophenyl)phosphino]ethane) (dfppe) due to the modulation of specific intermolecular interactions between the dmit ligand and Hg²⁺ ion. The structure exhibited a large pseudo-Stokes shift, which was advantageous for the internal reference signal and for eliminating potential artifacts. Straightforward chain-end manipulation enabled the tuning of chemosensor properties without additional chemical alterations. Based on these findings, we propose a new platform for improving the selectivity and sensitivity of colorimetric cation sensors. The results of this study will facilitate the designing of organic materials whose certain properties can be enhanced through precise control of the materials’ chemical hybridization by simple functional end-group manipulation. Full article

Metal dithiolene complexes—M(dmit)₂—are key building blocks for magnetic, conducting, and optical molecular materials, with singular electronic structures resulting from the mixing of the metal and dmit ligand orbitals. Their use in the design of magnetic and conducting materials is linked to the control of the unpaired electrons and their localized/delocalized nature. It has been recently found that UV–Vis light can control the spin distribution of some [Cu(dmit)₂]⁻² salts in a direct and reversible way. In this work, we study the optical response of these salts and the origin of the differences observed in the EPR spectra under UV–Vis irradiation by means of wave function-based quantum chemistry methods. The low-lying states of the complex have been characterized and the electronic transitions with a non-negligible oscillator strength have been identified. The population of the corresponding excited states promoted by the UV–Vis absorption produces significant changes in the spin distribution, and could explain the changes observed in the system upon illumination. The interaction between neighbor [Cu(dmit)₂]⁻² complexes is weakly ferromagnetic, consistent with the relative orientation of the magnetic orbitals and the crystal packing, but in disagreement with previous assignments. Our results put in evidence the complex electronic structure of the [Cu(dmit)₂]⁻² radical and the relevance of a multideterminantal approach for an adequate analysis of their properties. Full article

Hybrid ion-pair crystals involving hexadentate [Fe(III)(3-OMesal₂-trien)]⁺ spin-crossover (SCO) cationic complexes and anionic gold complexes [Au(dmit)₂]⁻ (1) (dmit = 4,5-dithiolato-1,3-dithiole-2-thione) and [Au(dddt)₂]⁻ (2) (dddt = 5,6-dihydro-1,4-dithiin-2,3-dithiolate) were synthesized and studied by single-crystal X-ray diffraction, P-XRD, and SQUID magnetometry. Our study shows that both complexes have similar 1:1 stoichiometry but different symmetry and crystal packing. Complex 1 has a rigid structure in which the SCO cations are engaged in strong π-interplay with molecular surrounding and does not show SCO transition while 2 demonstrates a reversible transition at T_sco = 118 K in a much “softer”, hydrogen-bonded structure. A new structural indicator of spin state in [Fe(sal₂-trien)]⁺ complexes based on conformational analysis has been proposed. Aging and thermocycling ruined the SCO transition increasing the residual HS fraction from 14 to 41%. Magnetic response of 1 is explained by the AFM coupled dimers S = 5/2 with J₁ = −0.18 cm⁻¹. Residual high-spin fraction of 2, apart from a contribution of the weak dimers with J₁₂ = J₃₄ = −0.29 cm⁻¹, is characterized by a stronger interdimer coupling of J₂₃ = −1.69 cm⁻¹, which is discussed in terms of possible involvement of neutral radicals [Au(dddt)₂]. Full article

In an isostructural series of anion radical salts β′-(Me_4-xEt_xZ)[Pd(dmit)₂]₂ (Z = P, As, Sb; x = 0, 1, 2), [Pd(dmit)₂]₂⁻ units form a two-dimensional Mott insulator layer with a quasi-isosceles triangular lattice. The anisotropy of the triangular lattice is characterized by a ratio of interdimer transfer integrals, t′/t. The crystal structures of EtMe₃Sb, Me₄Sb, Me₄As, and Et₂Me₂As salts were determined in the range of 5–295 K by the single crystal X-ray diffraction technique. Interdimer transfer integrals, Fermi surface, and band structures at low temperatures were calculated by the tight binding method and the first-principles density-functional theory (DFT) method based on experimentally obtained crystal structures. Interdimer transfer integrals increased with lowering temperature. At 5 K, the ratio t′/t decreased by about 15% from the room temperature value in every salt. The relationship between the transfer integrals and interdimer S⋯S distances indicated that the change of the t′/t value with temperature was due to a thermal contraction, rather than the arch-shaped molecular distortion of the Pd(dmit)₂ molecule associated with the cation dependence of t′/t. Full article

Photosensitive dyes often induce charge transfer (CT) between adjacent chemical species and themselves under irradiation of appropriate wavelengths. Because of the reversibility and selectivity of such CT, it is considered to be interesting to utilize such dyes as optically controllable trigger components for conduction and magnetism in the photoexcited states of organic materials. Based on this idea, such a type of new salts, i.e., γ- and δ-DiCC[Ni(dmit)₂] in addition to DiCC₂[Ni(dmit)₂]₃ have been prepared, characterized and their physical and structural properties have been examined both under dark and irradiated conditions (dmit²⁻ = 1,3-dithiole-2-thione-4,5-dithiolate, DiCC⁺ = 3,3′-Dihexyloxacarbocyanine monocation). Among them, under UV (254–450 nm) irradiation, δ-DiCC[Ni(dmit)₂] exhibited photoconductivity being six times as high as its dark conductivity at room temperature. The electron spin resonance (ESR) spectra have demonstrated that there are photoexcited spins on both DiCC and [Ni(dmit)₂] species as a result of the CT transition between them, serving as localized spins (DiCC) and carriers ([Ni(dmit)₂]), respectively. The results obtained in this work have indicated that the strategy mentioned above is effective in developing organic photoresponsive semiconductors with paramagnetism. Full article

We have prepared two dmit-based salts with a stable organic radical-substituted ammonium cation, (PO-CONH-C₂H₄N(CH₃)₃)[Ni(dmit)₂]₂·CH₃CN and (PO-CONH-C₂H₄N(CH₃)₃)[Pd(dmit)₂]₂ where PO is 2,2,5,5-Tetramethyl-3-pyrrolin-1-oxyl and dmit is 2-Thioxo-1,3-dithiol-4,5-dithiolate. The salts are not isostructural but have similar structural features in the anion and cation packing arrangements. The acceptor layers of both salts consist of tetramers, which gather to form 2D conducting layers. Magnetic susceptibility measurements indicate that the Ni salt is a Mott insulator and the Pd salt is a band insulator, which has been confirmed by band structure calculations. The cationic layers of both salts have a previously unreported polar structure, in which the cation dipoles order as ➚➘➚➘ along the acceptors stacking direction to provide dipole moments. The dipole moments of nearest neighbor cation layers are inverted in both salts, indicating no net dipole moments for the whole crystals. The magnetic network of the [Ni(dmit)₂] layer of the Ni salt is two-dimensional so that the magnetic susceptibility would be expected to obey the 1D or 2D Heisenberg model that has a broad maximum around T ≈ θ. However, the magnetic susceptibility after subtraction of the contribution from the PO radical has no broad maximum. Instead, it shows Curie–Weiss behavior with C = 0.378 emu·K/mol and θ = −35.8 K. The magnetic susceptibility of the Pd salt obeys a Curie–Weiss model with C = 0.329 emu·K·mol⁻¹ and θ = −0.88 K. Full article

Electrical and magnetic properties are dominated by the (de)localization and the anisotropy in the distribution of unpaired electrons in solids. In molecular materials, these properties have been indirectly controlled through crystal structures using various chemical modifications to affect molecular structures and arrangements. In the molecular crystals, since the energy band structures can be semi-quantitatively known using band calculations and solid state spectra, one can anticipate the (de)localization of unpaired electrons in particular bands/levels, as well as interactions with other electrons. Thus, direct control of anisotropy and localization of unpaired electrons by locating them in selected energy bands/levels would realize more efficient control of electrical and magnetic properties. In this work, it has been found that the unpaired electrons on Cu(II)-complex anions can be optically controlled to behave as anisotropically-delocalized electrons (under dark) or isotropically-localized electrons like free electrons (under UV), the latter of which has hardly been observed in the ground states of Cu(II)-complexes by any chemical modifications. Although the compounds examined in this work did not switch between conductors and magnets, these findings indicate that optical excitation in the [Cu(dmit)₂]²⁻ salts should be an effective method to control spin distribution and anisotropy. Full article

Strongly electron-lattice- and electron-electron-correlated molecular crystals, such as charge transfer (CT) complexes, are often sensitive to external stimuli, e.g., photoexcitation, due to the cooperative or competitive correlation of various interactions present in the crystals. These crystals are thus productive targets for studying photoinduced phase transitions (PIPTs). Recent advancements in research on the PIPT of CT complexes, especially Et₂Me₂Sb[Pd(dmit)₂]₂ and (EDO-TTF)₂PF₆, are reviewed in this report. The former exhibits a photoinduced insulator-to-insulator phase transition with clearly assigned spectral change. We demonstrate how to find the dynamics of PIPT using this system. The latter exhibits a photoinduced hidden state as an initial PIPT process. Wide energy ranged time-resolved spectroscopy can probe many kinds of photo-absorption processes, i.e., intra-molecular and inter-molecular electron excitations and intramolecular and electron-molecular vibrations. The photoinduced spectral changes in these photo-absorption processes reveal various aspects of the dynamics of PIPT, including electronic structural changes, lattice structural changes, and molecular deformations. The complexities of the dynamics of the latter system were revealed by our measurements. Full article

An isostructural series of anion radical salts, β'-(Et_xMe_4−xZ)[Pd(dmit)₂]₂ (x = 0–2, Z = P, As, Sb), with a quasi-triangular lattice comprising the dimer unit [Pd(dmit)₂]₂⁻ belong to a strongly correlated electron system with geometrical frustration. Intra and interdimer transfer integrals between the frontier molecular orbitals, which characterize the strength of electron correlation and degree of frustration, can be tuned by selection of the counter cation. We have systematically analyzed the crystal structure with X-ray diffraction method and intermolecular transfer integrals using extended Hückel molecular orbital calculations based on structural data. The variation in the cation affects the unit cell in a manner equivalent to an anisotropic pressure. Increasing the covalent radius of the central atom Z and the number of ethyl groups (x) in the cation leads to slight arching of the Pd(dmit)₂ molecule. This arch-shaped distortion of the Pd(dmit)₂ molecule modifies the interdimer transfer integrals in formation of the regular triangular dimer lattice. On the other hand, the intradimer transfer integral, which is correlated with the effective on-site Coulomb interaction of the dimer, is weakly dependent on the type of cation. Full article