Redox-triggered reversible modulation of intense near-infrared and visible absorption using a paddlewheel-type diruthenium(III) complex.

A new paddlewheel-type diruthenium complex with 2-amino-3-(trifluoromethyl)pyridine (amtfmp) [Ru2(amtfmp)4Cl2] ([1]), which shows intense and characteristic near-infrared (NIR) and visible absorption, has been developed and structurally characterized by single crystal X-ray diffraction (SCXRD) analyses. This complex exhibits reversible and dramatic NIR and visible electrochromic behavior from deep-blue ([1]) to pink ([1]-) due to the ON-OFF switching of its characteristic ligand-to-metal charge transfer (LMCT) and d-d absorption bands in response to an external voltage or chemical reagent such as decamethylcobaltocene (CoCp*2). The one-electron reduced species of [1], i.e., [CoCp*2][1], was successfully isolated and fully characterized via SCXRD, the temperature dependence of the magnetic susceptibility, and mass spectroscopy, proving that this electrochromic behavior occurs without significant structural reorganization of [1].

Large-Amplitude Thermal Vibration-Coupled Valence Tautomeric Transition Observed in a Conductive One-Dimensional Rhodium-Dioxolene Complex.

The exploration of dynamic molecular crystals is a fascinating theme for materials scientists owing to their fundamental science and potential application to molecular devices. Herein, a one-dimensional (1D) rhodium-dioxolene complex is reported that exhibits drastic changes in properties with the phase transition. X-ray photoelectron spectroscopy (XPS) revealed that the room-temperature (RT) phase is in a mixed-valence state, and therefore, the drastic changes originate from the mixed-valence state appearing in the RT phase. Another notable feature is that the mean square displacements of the rhodium atoms along the 1D chain dramatically increased in the RT phase, indicating a large-amplitude vibration of the Rh-Rh bonds. From these results, a possible mechanism for the appearance of the mixed-valence state in the RT phase was proposed based on the thermal electron transfer from the 1D d-band to the semiquinonato π* orbital coupled with the large-amplitude vibration of the Rh-Rh bonds.

Detailed magnetic analysis and successful deep-neural-network-based conformational prediction for [VO(dmso)5][BPh4]2.

Pentakis(dimethylsulfoxide-κO)oxidovanadium(iv) bis(tetraphenylborate), [VO(dmso)5][BPh4]2 (dmso: dimethylsulfoxide), was synthesized, and its pseudo-C 4 VO6 coordination geometry was revealed by a single-crystal X-ray method. A novel equation set was obtained for magnetic susceptibility and magnetization of the d1 complexes, considering the axial distortion and the spin-orbit coupling for the 2D free-ion term. The equation set enabled magnetic simulation for significantly symmetry-lowered d1 complexes to obtain the anisotropic g-values and also the excitation energies. In addition, conformational prediction was conducted, using the enumeration results on the basis of the group theory. The dominant conformers were predicted on the basis of the density functional theory (DFT) method, and especially, the conformer in the crystal was successfully predicted by a deep neural network method.

Paddlewheel-type diruthenium(iii,iii) tetrakis(2-aminopyridinate) complexes with NIR absorption features: combined experimental and theoretical study.

The reactions of [Ru2(O2CCH3)4Cl] with 2-aminopyridine (Hamp) and 2-amino-4-methylpyridine (Hammp) afforded two novel Ru2 complexes, [Ru2(amp)4Cl2] (1) and [Ru2(ammp)4Cl2] (2), respectively. Single crystal X-ray diffraction analyses revealed that 1 and 2 adopted typical paddlewheel-type structures, where the Ru2 units are coordinated with four aminopyridinate ligands with a cis-2:2 arrangement at the equatorial positions and two chloride ligands at the axial positions. The stabilities of 1 and 2 were supported by unrestricted density functional theory (uDFT) calculations. The zero-point energies of the three structural isomers (trans-2:2, 3:1, and 4:0 arrangements) of 1 and 2 were less stable than those of the respective cis-2:2 arrangements. Temperature-dependences of the magnetic susceptibility measurements and uDFT calculations showed that the oxidation and spin states of the Ru2 units in 1 and 2 were commonly Ru26+ and triplet states, respectively. Cyclic voltammetry showed that 1 and 2 underwent one-electron reduction processes, i.e., 1/1- and 2/2-, at redox potentials (E1/2) of -0.08 and -0.18 V vs. SCE, respectively. These results agreed well with the DFT-calculated E1/2 values of 1 (-0.08 V vs. SCE) and 2 (-0.18 V vs. SCE) and were theoretically attributed to Ru2-centred (δ*(Ru2)) redoxes. Moreover, 1 and 2 showed unique near-infrared absorption bands at approximately 1200-1500 nm, which were theoretically attributed to the ligand-to-metal charge transfer (LMCT) with π(amp or ammp) →δ*(Ru2) transition characteristics.

Proton Order-Disorder Phenomena in a Hydrogen-Bonded Rhodium-η(5)-Semiquinone Complex: A Possible Dielectric Response Mechanism.

A newly synthesized one-dimensional (1D) hydrogen-bonded (H-bonded) rhodium(II)-η(5)-semiquinone complex, [Cp*Rh(η(5)-p-HSQ-Me4)]PF6 ([1]PF6; Cp* = 1,2,3,4,5-pentamethylcyclopentadienyl; HSQ = semiquinone) exhibits a paraelectric-antiferroelectric second-order phase transition at 237.1 K. Neutron and X-ray crystal structure analyses reveal that the H-bonded proton is disordered over two sites in the room-temperature (RT) phase. The phase transition would arise from this proton disorder together with rotation or libration of the Cp* ring and PF6(-) ion. The relative permittivity εb' along the H-bonded chains reaches relatively high values (ca., 130) in the RT phase. The temperature dependence of (13)C CP/MAS NMR spectra demonstrates that the proton is dynamically disordered in the RT phase and that the proton exchange has already occurred in the low-temperature (LT) phase. Rate constants for the proton exchange are estimated to be 10(-4)-10(-6) s in the temperature range of 240-270 K. DFT calculations predict that the protonation/deprotonation of [1](+) leads to interesting hapticity changes of the semiquinone ligand accompanied by reduction/oxidation by the π-bonded rhodium fragment, producing the stable η(6)-hydroquinone complex, [Cp*Rh(3+)(η(6)-p-H2Q-Me4)](2+) ([2](2+)), and η(4)-benzoquinone complex, [Cp*Rh(+)(η(4)-p-BQ-Me4)] ([3]), respectively. Possible mechanisms leading to the dielectric response are discussed on the basis of the migration of the protonic solitons comprising of [2](2+) and [3], which would be generated in the H-bonded chain.

Multifunctional one-dimensional rhodium(I)-semiquinonato complex: substituent effects on crystal structures and solid-state properties.

Two new one-dimensional (1D) rhodium(I)-semiquinonato complexes formulated as [Rh(3,6-DBSQ-4,5-PDO)(CO)2]∞ (4; 3,6-DBSQ-4,5-PDO(•-) = 3,6-di-tert-butyl-4,5-(1,3-propanedioxy)-1,2-benzosemiquinonato) and [Rh(3,6-DBSQ-4,5-(N,N'-DEN))(CO)2]∞ (5; 3,6-DBSQ-4,5-(N,N'-DEN)(•-) = 3,6-di-tert-butyl-4,5-(N,N'-diethylenediamine)-1,2-benzosemiquinonato) were synthesized to explore the nature of the unusual structural phase transition and magnetic and conductive properties recently reported for [Rh(3,6-DBSQ-4,5-(MeO)2)(CO)2]∞ (3; 3,6-DBSQ-4,5-(MeO)2(•-) = 3,6-di-tert-butyl-4,5-dimethoxy-1,2-benzosemiquinonato). Their crystal structures and magnetic and conductive properties were investigated. Compounds 4 and 5 comprise neutral 1D chains of complex molecules stacked in a staggered arrangement with fairly short average Rh-Rh distances of 3.06 Å for 4 and 3.10 Å for 5. These distances are similar to those for 3 (3.09 Å); however, the molecules of 5 are strongly dimerized in the 1D chain. Compound 4 undergoes a first-order phase transition at Ttrs = 229.1 K, and its magnetic properties drastically change from antiferromagnetic coupling in the room-temperature (RT) phase to strong ferromagnetic coupling in the low-temperature (LT) phase. In addition, compound 4 exhibits a long-range ordering of net magnetic moments originating from the imperfect cancellation of antiferromagnetically coupled spins between the ferromagnetic 1D chains at TN = 10.9 K. Furthermore, this compound exhibits an interesting crossover from a semiconductor with a small activation energy (Ea = 31 meV) in the RT phase to a semiconductor with a large activation energy (Ea = 199 meV) in the LT phase. These behaviors are commonly observed for 3. Alternating current susceptibility measurements of 4, however, revealed a frequency-dependent phenomenon below 5.2 K, which was not observed for 3, thus indicating a slow spin relaxation process that possibly arises from the movements of domain walls. In contrast, compound 5, which possesses a strongly dimerized structure in its 1D chain, shows no sign of strong ferromagnetic interactions and is an insulator, with a resistivity greater than 7 × 10(7) Ω cm.

Bistable multifunctionality and switchable strong ferromagnetic-to-antiferromagnetic coupling in a one-dimensional rhodium(I)-semiquinonato complex.

We present a comprehensive study of the synthesis, heat capacity, crystal structures, UV-vis-NIR and mid-IR spectra, DFT calculations, and magnetic and electrical properties of a one-dimensional (1D) rhodium(I)-semiquinonato complex, [Rh(3,6-DBSQ-4,5-(MeO)2)(CO)2]∞ (3), where 3,6-DBSQ-4,5-(MeO)2(•-) represents 3,6-di-tert-butyl-4,5-dimethoxy-1,2-benzosemiquinonato radical anion. The compound 3 comprises neutral 1D chains of complex molecules stacked in a staggered arrangement with short Rh-Rh distances of 3.0796(4) and 3.1045(4) Å at 226 K and exhibits unprecedented bistable multifunctionality with respect to its magnetic and conductive properties in the temperature range of 228-207 K. The observed bistability results from the thermal hysteresis across a first-order phase transition, and the transition accompanies the exchange of the interchain C-H···O hydrogen-bond partners between the semiquinonato ligands. The strong overlaps of the complex molecules lead to unusually strong ferromagnetic interactions in the low-temperature (LT) phase. Furthermore, the magnetic interactions in the 1D chain drastically change from strongly ferromagnetic in the LT phase to antiferromagnetic in the room-temperature (RT) phase with hysteresis. In addition, the compound 3 exhibits long-range antiferromagnetic ordering between the ferromagnetic chains and spontaneous magnetization because of spin canting (canted antiferromagnetism) at a transition temperature T(N) of 14.2 K. The electrical conductivity of 3 at 300 K is 4.8 × 10(-4) S cm(-1), which is relatively high despite Rh not being in a mixed-valence state. The temperature dependence of electrical resistivity also exhibits a clear hysteresis across the first-order phase transition. Furthermore, the ferromagnetic LT phase can be easily stabilized up to RT by the application of a relatively weak applied pressure of 1.4 kbar, which reflects the bistable characteristics and demonstrates the simultaneous control of multifunctionality through external perturbation.

On the nature of the multiple ground states of the MMX mixed-valence chain compound, [Pt(II/III)2(n-PenCS2)4I]∞.

We present a comprehensive study of the temperature dependence of the crystal structure using single-crystal X-ray diffraction and diffuse scattering, and electrical transport and magnetic properties as well as some optical properties at room temperature to elucidate the origin and the form of multiple ground states demonstrated in a previous study of the heat-capacity of the MMX chain compound, [Pt(II/III)(2)(n-PenCS(2))(4)I](∞). The present results confirm the presence of the two phase transitions, one reversible of first order at 207 K and the other nonreversible monotropic at 324 K, separating the low temperature (LT), room temperature (RT), and high temperature (HT) phases. The unit cell displays a 3-fold periodicity of -Pt-Pt-I- in the RT and HT phases because of the structural disorder which is exhibited by the dithiocarboxylato groups and the n-pentyl groups belonging to the central diplatinum unit. In addition, for the HT-phase all the dimers show this disorder. This compound undergoes a metal-semiconductor transition at T(M-S) = 235 K. The presence of diffuse streaks corresponding to 2-fold -Pt-Pt-I- periodicity in the HT and RT phases indicates dynamic valence ordering of the type -Pt(2+)-Pt(2+)-I(-)-Pt(3+)-Pt(3+)-I(-)-or-Pt(2+)-Pt(3+)-I(-)-Pt(3+)-Pt(2+)-I(-)-. For the LT-phase the diffuse scattering is condensed into clear Bragg diffraction peaks while keeping the 3-fold periodicity. This fact suggests further localization through dimerization of charges and spins confirming the diamagnetic state in the magnetic susceptibility and the low electrical conduction below 207 K. The present results are further discussed in relation to those of previous studies on the homologues, [Pt(II/III)(2)(RCS(2))(4)I](∞), R = methyl, ethyl, n-propyl, and n-butyl.

Syntheses, structures and solid-state properties of MMX mixed-valence chains, [Ni(II/III)2(RCS2)4I]infinity (R = Et, n-Pr and n-Bu): evidence of a spin-Peierls transition.

The partial oxidation of [Ni(II/II)(2)(RCS(2))(4)] (R = Et (1), n-Pr (2), and n-Bu (3)) with iodine affords the MMX chain compounds [Ni(II/III)(2)(RCS(2))(4)I](infinity) (R = Et (4), n-Pr (5), and n-Bu (6)), respectively. The crystal structures of 4-6 consist of neutral one-dimensional (1-D) chains with a repeating -Ni-Ni-I- unit. The room-temperature (RT) structure of 4 indicates a charge-polarization (CP) state {-Ni((2.5-delta)+)-Ni((2.5+delta)+)-I(-)-Ni((2.5-delta)+)-Ni((2.5+delta)+)-I(-)- (delta << 0.5)} close to an averaged valence state judged by the Ni-I distances. In contrast, 5 and 6 exhibit a 3-fold periodicity of a -Ni-Ni-I- unit due to the disorder of the dithiocarboxylato ligands. Compounds 4-6 show typical semiconducting behavior and exhibit an intense sharp absorption band centered at 5400 cm(-1), which is attributed to a Mott-Hubbard gap due to a relatively large on-site Coulomb repulsion energy U of the nickel atoms. The high-temperature magnetic susceptibilities of 4-6 can be described by a 1-D Heisenberg antiferromagnetic chain model with |J|/k(B) ranging from 898(2) to 939(3) K. Compounds 4 and 5 undergo a spin-Peierls (SP) transition at relatively high T(sp) = 47 and 36 K, respectively, which are accompanied by superlattice reflections corresponding to a 2-fold -Ni-Ni-I- period below T(sp). By determining the superstructure of 4 at 26 K, we conclude that the valence-ordered state changes from the CP in the RT phase to the alternate charge-polarization (ACP) state of -Ni((2.5-delta)+)-Ni((2.5+delta)+)-I(-)-Ni((2.5+delta)+)-Ni((2.5-delta)+)-I(-)- in the SP phase. Such a spin-Peierls transition could not be observed for 6.

Constructing highly conducting metal-metal bonded solids by electrocrystallization of [Pt(II)2(RCS2)4] (RCS2(-) = dithiocarboxylato, R = methyl or ethyl).

Partially oxidized one-dimensional (1D) Pt-Pt chain compounds [Pt2(MeCS2)4]4ClO4.5PhCN (1) and [Pt2(EtCS2)4]5(ClO4)2 (2) were synthesized by electrocrystallization of diplatinum(II,II) complexes from different solvents. 1 and 2 consist of 1D Pt-Pt chains of stacked Pt-Pt dimers with short interdimer S...S contacts. Depending on the number of ClO4- per dimer and their positions, 1 forms a regular stack of Pt-Pt dimers, whereas 2 forms pentamer of dimers in the 1D chain. 1 exhibits high electrical conductivity (4.2-8.0 S cm-1) at 300 K and metallic behavior above 125 K. 2 is a semiconductor. 1 exhibits almost temperature independent magnetic susceptibility (ca. 1.1 x 10-4 emu mol-1) which is attributed to Pauli paramagnetism, whereas the spin degree of freedom in 2 has been lost. Although the basic structures are closely related, they exhibited different solid-state properties that depend on the valence state of the platinum atoms and the periodicity within the 1D chain.

Alkyl group as entropy reservoir in an MMX chain complex, Pt2(n-PenCS2)4I.

Heat capacity of halogen-bridged one-dimensional binuclear metal complex (so-called MMX chain) having four n-pentyl groups, Pt2(n-PenCS2)4I, was measured by adiabatic calorimetry. A first-order phase transition was observed at 207.4 K when measurement was made after cooling from room temperature. The enthalpy and entropy of transition were determined to be 10.19 kJ mol(-1) and 49.1 J K(-1) mol(-1), respectively. A monotropic phase transition was observed at 324 K on heating, and the entropy of transition was essentially null. The sample once heated above 324 K never returned to the initial phase at room temperature and underwent a higher-order phase transition at 173 K and a first-order phase transition at 220.5 K. The enthalpy and entropy of the first-order phase transition were estimated to be 11.6 kJ mol(-1) and 52.4 J K(-1) mol(-1), respectively. The magnitude of the entropy gain at the phase transition from the initial room-temperature phase to the high-temperature phase at 324 K shows that in Pt2(n-PenCS2)4I a large amount of entropy reserved in alkyl chain is transferred to dithiocarboxylato groups upon the phase transition, as in the cases of Pt2(n-PrCS2)4I and Pt2(n-BuCS2)4I.