Hydrogen‐Bonded Polyrotaxane Cation Structure in Nickel Dithiolate Anion Radical Salts: Ferromagnetic and Semiconducting Behavior Associated with Structural Phase Transition

Abstract

The pseudo‐polyrotaxane structure of [(H‐bpy+)‐ (DB‐24‐crown‐8)]∞ (H‐bpy+ = monoprotonated 4,4‐bipyridinium; DB‐24‐crown‐8 = dibenzo‐24‐crown‐8) has been incorporated into the anion radical salt [Ni(dmit)2]− (dmit2− = 1,3‐dithiole‐2‐thione‐4,5‐dithiolate). (H‐bpy+)(DB‐24‐crown‐8)[Ni(dmit)2]− crystallized as two polymorphs, crystals 1 and 2. Crystal 1 was found to have a lower density and looser packing structure in which H‐bpy+ forms a one‐dimensional hydrogen‐bonding chain that passes though the crown ether ring of DB‐24‐crown‐8. DB‐24‐crown‐8 adopts a U‐shaped conformation in which two phenylene rings sandwich one of the pyridyl rings of H‐bpy+ to stabilize the structure. The [Ni(dmit)2]− anions are arranged in a layer parallel to the (10) plane with uniform side‐by‐side interactions. A structural phase transition was observed at 235 K, accompanied by ordering of the polyrotaxane structure. In crystal 1, at 173 K, H‐bpy+ is twisted around the central C−C bond, which perturbs the arrangement of [Ni(dmit)2]− through short C−H⋅⋅⋅S contacts. As a result, the semiconducting behavior, with an activation energy of 0.21 eV, becomes insulating below 235 K. The crystal exhibits ferromagnetic interactions because of the weak side‐by‐side interactions between [Ni(dmit)2]− anions. Crystal 2 has a similar pseudo‐polyrotaxane structure but showed no phase transition. This suggests that the looser crystal packing in crystal 1 induces the structural change of the pseudo‐polyrotaxane, perturbing the electron system of [Ni(dmit)2]−.

Uniaxial negative thermal expansion induced by molecular rotation in a one-dimensional supramolecular assembly with associated peculiar magnetic behavior

“…Previous studies have reported that [24]crown-8 derivatives can include heteroaromatic cations within their cavities. [26][27][28][29] We previously reported the salt (H-bpy + )(DB [24]crown-8)[Ni(dmit) 2 ] À (H-bpy + = monoprotonated 4,4 0 -bipyridine), 30 in which one of the pyridyl rings of H-bpy + is completely included in the DB [24]crown-8 cavity, sandwiched between its phenylene rings. The H-bpy + molecules form one-dimensional (1D) hydrogen-bonded chains and act as pseudo-polyrotaxanes, where one of the two pyridyl rings rotates.…”

Switchable Dielectric Phase Transition with Drastic Symmetry Breaking in a Sn(IV)-Based Perovskite-Type Halide Semiconductor

“…Switchable stimuli-responsive materials, showing compelling richness in terms of potential applications in the fields of data storage, signal processing and sensing, data communication, and optical technologies, have become a popular direction of modern material research. − The switching behaviors tuned by externally induced stimuli, such as light, temperature, electric field, and pressure, have brought great impetus for the exploration of dielectric, piezoelectric, pyroelectric, and ferroelectric properties. − Among them, the dielectric property manifests collective behavior of polarizable bound charges. The degree of polarizability is described by the real part ε′ of the dielectric constant, ε = ε′ – i ε″, where ε″ is the imaginary part. − The ε′ of the switchable dielectric material displays an obvious anomaly between high and low dielectric states around T c , which are mainly due to the dynamic or motional transformations between disordered and ordered states and the displacement in molecules or ions. − Such changes usually accompany with the structural phase transition and often provoke symmetry breaking with the temperature decreasing. − Consequently, it is an effective way to find novel responsive switchable compounds composed of temperature-sensitive flexible components to enrich the family of dielectric materials and promote the process of application in smart devices.…”

Insight into the Properties of Heteroleptic Metal Dithiolenes: Multistimuli Responsive Luminescence, Chromism, and Nonlinear Optics

“…Analytical results are in accordance with the formula n- n-Bu 4 N[Pd((R)-α-MBAdto)(quinoxdt)] (5). Na (9.2 mg, 0.4 mmol) was added to 15 mL of MeOH; the resulting solution was added dropwise to a stirred suspension of [1,3]dithiolo [5,6][1,4]dithiino [2,3-b]quinoxalin-2-one (59.1 mg, 0.18 mmol) in 50 mL of 50% MeOH/50% CHCl 3 . The mixture was stirred for 30 min at room temperature to give a reddish brown dithiolate solution.…”

“…The interest in metal dithiolene chemistry in basic science , and in various fields of materials chemistry − has been fueled by the growing attention to heteroleptic derivatives with potential application in dye-sensitized solar cells − or in second-order nonlinear optics (NLO). , By well-established engineering, these complexes can be obtained as planar and low-energy-gap molecules consisting of a π-acceptor (A) and a π-donor (D) ligand connected by a d 8 metal in a square-planar coordination, where the metal acts as a suitable π-bridge for the D–A charge transfer (CT) transition. Several other classes of complexes, where a d 8 metal (mostly platinum) connects a variety of suitably engineered D–A ligands, are of interest for their NLO and photoemissive properties as well as in photocatalysis .…”