Xuan-Rong Chen

A facile route for preparation of monodisperse nanoparticles of one-dimensional Fe(II)-4-amino-1,2,4-triazole coordination polymers with hysteretic spin-crossover near room temperature

Spin-crossover (SCO) occurring in a transition metal complex is the switchable process between two spin states in response to external perturbations such as changes in temperature, pressure or photoexcitation. Such a material has potential applications in switching devices. In this study, we designed a one-dimensional spin-crossover polymer, with a formula of [Fe(NH2-Trz)3](doe)2 where NH2-Trz = 4-amino-1,2,4-triazole and doe = sodium dodecyl sulfonate, and fabricated its monodisperse nanoparticles using a facile precipitation route. The nanoparticles aggregate from plate-shaped nanocrystals and their size dimensions fall in the range of 200–300 nm. The SCO polymer undergoes a thermal reversible spin transition near room temperature which is important for practical applications. The spin transition shows ca. 13 K hysteretic loops and is associated with a color change. The SCO polymer nanoparticles were pressed under ca. 8 MPa static pressure to give a good transparent disc with a thickness of ca. 1 mm; such a disc displays a pink-violet color at ambient temperature and a yellowish color above 45 °C. This SCO material has potential applications in the field of thermochromic devices.

Influence of the molecular structures of dithiolate ligands on crystal packing modes and magnetic properties in salts (Bz-Et3N)[Ni(dmit)x(mnt)2−x] (x = 0–2)

Nickel-bis-dithiolene salts, (Bz-Et3N)[Ni(dmit)x(mnt)2−x] (x = 0–2 for 1–3 and mnt2− = maleonitriledithiolate, dmit2− = 2-thioxo-1,3-dithiole-4,5-dithiolate), have been prepared and characterized. These three salts exhibit distinct anion packing structures and magnetic properties. [Ni(mnt)2]− anions, in which the mnt2− ligand has a reduced number of sulfur atoms, form one-dimensional anion stacks in 1. Conversely, [Ni(dmit)2]− anions, in which the dmit2− ligand contains extended SR groups, give rise to a layered structure in 2; the anion layer is composed of co-facial [Ni(dmit)2]− dimers, which are interconnected through short lateral-to-lateral S⋯S and head-to-tail S⋯S contacts. The heteroleptic [Ni(dmit)(mnt)]− anions show one-dimensional anion stacking in 3. Charge-assisted H-bonds are formed between the CN groups of the mnt2− ligands and the H atoms of the cations in 1 and 3 and between the terminal S atoms of the dmit2− ligands and the H atoms of the cations in 2. Both 1 and 3 show antiferromagnetic chain behavior. Within the respective magnetic chains, there are much stronger antiferromagnetic interactions in 3 than in 1, and salt 2 shows antiferromagnetic dimer behavior.

Phase Transition, Dielectrics, Single-Ion Conductance, and Thermochromic Luminescence of a Inorganic–Organic Hybrid of [Triethylpropylammonium][PbI3]

In this study, we used the facile solvent evaporation method to achieve the inorganic-organic hybrid crystals of [triethylpropylammonium][PbI3], which have been characterized by elemental analysis, IR spectroscopy, thermogravimetric analysis, and differential scanning calorimetry as well as single-crystal X-ray structure analysis. The hybrid solid crystallizes in the monoclinic space group P21/c at room temperature and is composed of one-dimensional [PbI3]∞ chains, where the neighboring PbI6 coordination octahedra connect together via the face-sharing mode and the organic cations fall in the spaces between [PbI3]∞ chains. The hybrid exhibits a dielectric phase transition with a critical temperature of ca. 432 K, dielectric relaxation at frequencies below 107 Hz, and single-ion conducting behavior, the conductivity of which increases rapidly from 9.43 × 10-10 S cm-1 at 383 K to 4.47 × 10-5 S cm-1 at 473 K. The variable-temperature single-crystal and powder X-ray diffraction analyses revealed that the dielectric phase transition is related to the disorder-to-order transformation of cations in the lattice. The electric modulus and impedance spectral analyses further disclosed that the dielectric relaxation arises from the ionic displacement polarization and molecular dipole orientation of cations. The single-ion conductance is due to the migration of cations that fall in the spaces of rigid inorganic [PbI3]∞ chains. The phase transition gives rise to this hybrid showing switchable ion-conducting nature around the critical temperature of the phase transition. Besides the fascinating functionalities mentioned above, the hybrid also exhibits a thermochromic luminescence feature originating from the electron transition between the valence and conduction bands of the inorganic [PbI3]∞ chain.

Two magnetic phase transitions, driven by symmetry breaking and isostructural phase transitions, in a nickel-bis-dithiolene spin system

A one-dimensional (1-D) magnetic chain compound, [(CD3)2CN-Py][Ni(mnt)2], where (CD3)2CN-Py+ = 1-(propan-d6-2-ylideneamino)pyridinium and mnt2− = maleonitriledithiolate, was synthesized and characterized. This compound undergoes two structural phase transitions, at around 267 K and 325 K. The three phases are sequentially labeled as α (below 267 K), β (between 267 and 325 K) and γ (above 325 K). The [Ni(mnt)2]− anions form irregular stacks, with two values of neighboring Ni⋯Ni distances. The cations align in a straight and regular arrangement along the crystallographic a-axis direction in the β phase. The asymmetric unit switches from one anion–cation pair to two anion–cation pairs in the transition from the β to the α phase. This leads to a doubling of the crystallographic axis length, parallel to the anion stack. It also results in the irregular anion stack showing three non-equivalent neighboring Ni⋯Ni distances, as well as making the straight cation arrangement irregular. The β and γ phases are isostructural and exhibit quite similar packing structures. The anion stack shrinks a little with increasing temperature, with all crystallographic axes showing small reduction from the β to γ phase. The two observed magnetic phase transitions are driven by these various structural phase transitions. A thermal hysteresis loop, with a separation of ∼8 K, appears in the transition between the β and α phases. However, this is absent in the transition between the β and γ phases. A dielectric anomaly appears across the phase transition between the β and γ phases but not between the β and α phases.