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Subtle integration of rotatable polar components into dielectric crystals can contribute significantly to adjustable switching temperatures ( T s ) and dielectric relaxation behaviors. Currently, one of the biggest challenges lies in the design of optimal polar components with moderate motion resistance in a crystalline system. In this work, we demonstrate that under refrigerator conditions, rotatable hydrogen-bonded one-dimensional (1D) cationic chains, {[C 2 H 6 N 5 ] + } n (C 2 H 6 N 5 = 3,5-diamino-1,2,4-triazolinium), and two-dimensional (2D) anionic layers, {[(H 2 O) 2 ·SO 4 ] 2- } n , can be generated in an organic salt, 3 ([C 2 H 6 N 5 ] 2 ·[(H 2 O) 2 ·SO 4 ]). Compared with the nonhydrated precursor, 2 ([C 2 H 7 N 5 ]·[SO 4 ]), the rotation of these 1D and 2D ionic species triggers a reversible phase transition and dielectric switching in 3. In addition, the significantly sluggish rotation of the 1D cationic chains from parallel to unparallel stacking and the counter-clockwise rotation of the 2D anionic layers, compared with their reverse processes, induce a frequency-dependent dielectric response with a more highly adjustable heating T s ↑ than the cooling T s ↓. More importantly, 3 possesses excellent self-recovery ability attributed to the highly dynamic character of the hydrogen-bonded ionic species. The strategy here can provide a fairly good model for designing dielectric crystals with desired rotatable polar components.

Combining the fascinating advantages of ultrathin two-dimensional (2D) nanosheets with the nanostructuration of spin-crossover (SCO) materials represents an attractive target of controlled fabrication of SCO nano-objects at the device level. Here, we demonstrate that through facile-operating ultrasonic force-assisted liquid exfoliation technology the three-dimensional (3D) van der Waals SCO bulk precursor {[Fe(1,3-bpp) 2 (NCS) 2 ] 2 (1, 1,3-bpp = 1,3-di(4-pyridyl)-propane)} can be exfoliated into single-layered 2D nanosheets (NS-1). As a consequence, the magnetism has been tuned from complete paramagnetic (bulk precursors) to SCO transition at around 250 K (2D nanosheets). In addition, the metal-to-ligand charge transition (MLCT), the intraligand π-π* transition and the color display also have been altered both in colloidal suspension and in the solid state. These dramatic changes of physical-chemical properties at different forms and states can be attributed to the efficient cooperativity derived from the interlayer van der Waals interactions within the curly or vertically stacked 2D building blocks.

Through a facile-operating ultrasonic force-assisted liquid exfoliation technology, the single-layered two-dimensional (2D) [Co(CNS) 2 (pyz) 2 ] n (pyz = pyrazine) nanosheets, with a thickness of sub-1.0 nm, have been prepared from the bulk precursors. The atomically thickness and the presence of abundant sulfur atoms with high electronegativity arrayed on the double surfaces of the sheets are making this kind of 2D MOF (metal-organic framework) nanosheets highly sensitive to intermolecular interactions. As a result, it can be well dispersed in all kinds of solvents to give a stable colloidal suspension that can be maintained for at least one month, accompanied by significant solvatochromic behavior and various optical properties, which thus have shown the potential to be practically applicated as in situ visual test paper for solvent identification and solvent polarity measurements. More importantly, combined with a smartphone, this kind of 2D-MOF nanosheets can be developed into in situ visual test paper to identify isomers and determine the polarity of mixed solvents quantitatively and qualitatively, suggesting the promising application of a portable, economical, and in situ visual test strategy in real world.

Bidirectional photoswitching of molecular materials under ambient condition is of significant importance. Herein, we present for the first time that a core-shell UCNP-SCO nanosphere (UCNP = upconversion nanophosphor, SCO = spin crossover), which was composed of a UCNP core (NaYF 4 : 20 mol % Yb 3+ , 1 mol % Er 3+ ) and an SCO iron(II) shell ([Fe(H 2 Bpz) 2 (bipy-COOH)], H 2 Bpz = dihydrobis(1-pyrazolyl)borate, bipy-COOH = 4,4'-dicarboxy-2,2'-bipyridine), can be reversibly photoswitched between the high-spin and low-spin states at room temperature in the solid state, via alternating irradiation with near-infrared (λ = 980 nm) and ultraviolet (λ = 310 nm) light. What's more, this reversible spin-state switching was accompanied by a variation of fluorescent spectrum and dielectric constants. The strategy here, that is, integrating the SCO iron(II) complex into a UCNP-SCO nanosphere for molecular photoswitching, may open a new area in the development of photocontrolled molecular devices.

A thermal-induced dielectric switching has been realized in two ion-pair crystal [C 2 H 6 N 5 ] + ·[H 2 PO 4 ] - (1, C 2 H 6 N 5 = 3,5-diamino-1,2,4-triazolinium) through single-crystal-to-single-crystal phase transition (SCSC-PT). Upon cooling from room temperature, the 1D cation stripes that are composed of [C 2 H 5 N 5 ] + cations have undergone a 90° sharp rotation around the c axis, accompanied by the transition of crystal stacking from loose unparallel (dynamic state) to compression parallel (static state) and reorientation of dipoles on the [C 2 H 5 N 5 ] + cation, which thus resulted in high dielectric state to low dielectric state transformation. While on the warming run, the reverse process was rather sluggish, resulting in a reversible dielectric switching with ultralarge (about 40K wide) hysteresis loop near room temperature. It is thought that the large-sized polar cation stripes have a predominant influence on the switching properties of 1.

The organometallic cation 1 (Fe(bipy-NH 2 ) 3 2+ , bipy-NH 2 = 4,4'-diamino-2,2'-bipyridine), which was constructed in situ in solution, can bind CO 2 from air effectively with a stoichiometric ratio of 1:4 (1/CO 2 ), through the formation of "H-bonded CO 2 " species: [CO 2 -OH-CO 2 ] - and [CO 2 -CO 2 -OH] - . These two species, along with the captured individual CO 2 molecules, connected 1 into a novel 3D (three-dimensional) architecture, that was crystal 1·2(OH - )·4(CO 2 ). The adsorption isotherms, recycling investigations, and the heat capacity of 1 have been investigated; the results revealed that the organometallic cation 1 can be recycled at least 10 times for the real-world CO 2 capture applications. The strategies presented here may provide new hints for the development of new alkanolamine-related absorbents or technologies for CO 2 capture and sequestration.

In the title compound, C(9)H(6)FNO(2), all the non-H atoms are approximately coplanar, the carb-oxy O atoms deviating by 0.0809 and -0.1279 Å from the indole plane. In the crystal, O-H⋯O hydrogen bonds link the mol-ecules into dimers which are linked via N-H⋯O hydrogen bonds and π-π inter-actions [centroid-centroid distance = 3.680 (2) Å].

In the title compound, C(11)H(10)N(2), the carbonitrile group is twisted away from the indole plane [C(cy)-C(me)-C(ar)-C(ar) = 66.6 (2)°; cy = cyanide, me = methyl-ene and ar = aromatic]. In the crystal, N-H⋯N hydrogen bonds link the mol-ecules into C(7) chains propagating in the [001] direction.

In the title compound, C(9)H(6)ClNO, the Cl atom deviates by 0.142 (1) Å from the quinoline ring mean plane (r.m.s. deviation = 0.013 Å). In the crystal, N-H⋯O hydrogen bonds link the mol-ecules into [010] C(4) chains. Aromatic π-π stacking inter-actions [shortest centroid⋯centroid distance = 3.685 (3) Å] are also observed.

In the title compound, C(9)H(6)ClNO(2), the carboxyl group is twisted from the indole ring system by 9.00 (8)°. In the crystal, inversion dimers linked by pairs of O-H⋯O hydrogen bonds generate R(2) (2)(8) loops and N-H⋯O hydrogen bonds link the dimers into (001) sheets. Aromatic π-π stacking inter-actions [centroid-centroid distance = 3.7185 (12) A °] are also observed.

In the title compound, C(11)H(10)N(2)O, the cyanide group is twisted away from the indole-ring plane [C(cy)-C(me)-C(ar)-C(ar) = 70.7 (2)°; cy = cyanide, me = methyl-ene, ar = aromatic], whereas the meth-oxy C atom is almost coplanar with the ring system [displacement = 0.014 (5) Å]. In the crystal, N-H⋯N hydrogen bonds link the mol-ecules into C(7) chains propagating in [100].

The title compound, C(16)H(13)N, is essentially planar [maximum deviation from the least-squares plane = 0.081 (3) Å], with a dihedral angle of 1.65 (13)° between the planes of the indole and benzene rings. In the crystal, there are no significant inter-molecular π-π inter-actions [minimum ring centroid-centroid separation = 4.217 (5) Å].

In the crystal structure of the title compound, C(8)H(5)NO(6), both carboxyl groups are involved in inter-molecular centrosymmetric cyclic O-H⋯O hydrogen-bonding associations, which give a zigzag chain structure extending along (2[Formula: see text]1). Weak π-π stacking inter-actions are also present [minimum ring centroid separation = 3.893 (4) Å].

In the title compound, C(17)H(12)N(2), the inter-planar angle between the indole mean plane [max.deviation 0.030 (1) Å] and the phenyl ring is 24.32 (7)°. In the crystal, inter-molecular N-H⋯N C hydrogen bonds form zigzag chains in the a-axis direction augmented by weak C-H⋯N C contacts.

The title compound, C(10)H(7)ClN(2), contains two approximately planar mol-ecules, A and B (r.m.s. deviations = 0.039 and 0.064 Å, respectively) in the asymmetric unit. In the crystal, N-H⋯N hydrogen bonds link the mol-ecules into C(7) chains of alternating A and B mol-ecules propagating along the a-axis direction. The crystal used for the data collection was found to be a racemic twin.

In the title compound, C(10)H(7)ClN(2), the carbonitrile group is twisted away from the plane of the indole ring system [C(cy)-C(me)-C(ar)-C(ar) = -44.7 (8)°; cy = cyanide, me = methyl-ene and ar = aromatic]. In the crystal, N-H⋯N hydrogen bonds link the mol-ecules into C(7) chains propagating in [010]. Aromatic π-π stacking inter-actions [minimum centroid-centroid separation = 3.663 (3) Å] are also observed.

In the title compound, C(11)H(10)N(2)O, the O atom and the C atom of the methyl-ene group deviate only slightly [0.029 (3) and 0.055 (3) Å, respectively] from the approximately planar ring system (r.m.s. deviation = 0.013 Å). In the crystal, N-H⋯O hydrogen bonds link the mol-ecules into zigzag chains running along the b axis.

In the title compound, C(9)H(6)FNO(2), the carboxyl group is twisted slightly away from the indole-ring plane [dihedral angle = 7.39 (10)°]. In the crystal, carboxyl inversion dimers linked by pairs of O-H⋯O hydrogen bonds generate R(2) (2)(8) loops and N-H⋯O hydrogen bonds connect the dimers into (10[Formula: see text]) sheets.

In the crystal structure of the title compound, C(5)H(5)NO(3), all the non-H atoms are approximately coplanar: the carb-oxy O atoms deviating by 0.013 (2) and -0.075 (2) Å from the isoxazole ring plane. In the crystal, the molecules form inversion dimers linked by pairs of O-H⋯O hydrogen bonds and the dimers stack via π-π inter-actions [centroid-centroid distance = 3.234 (2) Å].

All non-H atoms of the title compound, C(7)H(7)NO(2), are nearly coplaner, the r.m.s. deviation being 0.0087 Å. In the crystal, the partially overlapped arrangement and the face-to-face distance of 3.466 (17) Å between parallel pyridine rings of neighboring mol-ecules indicates the existence of π-π stacking. Inter-molecular O-H⋯N hydrogen bonding and weak C-H⋯O hydrogen bonding are present in the crystal structure.

In the title compound, [CoCl(2)(C(13)H(20)N(4))]·H(2)O, the Co(II) atom lies on a mirror plane and is four-coordinated by two N atoms of the imidazole ligand and two Cl atoms in a distorted tetra-hedral arrangement. The water mol-ecule participates in the formation of hydrogen bonds, resulting in a three dimensional network involving the Cl atoms and the NH groups. The terminal C atom of the ethyl group is disordered over two sites of equal occupancy.

In the title compound, [Ni(NO(3))(C(13)H(20)N(4))(2)]NO(3), the Ni(II) ion shows a distorted octa-hedral geometry formed by four N atoms from two bis-(2-ethyl-5-methyl-1H-imidazol-4-yl)methane ligands and two O atoms from a chelating nitrate anion. Three ethyl groups in the complex cation and the O atoms of the uncoordinated nitrate anion are disordered over two sets of positions [occupancy ratios of 0.52 (3):0.48 (3) and 0.63 (3):0.37 (3), respectively]. In the crystal, inter-molecular N-H⋯O hydrogen bonds connect the complex cations into a zigzag chain along [010] and further N-H⋯O hydrogen bonds between the chains and the uncoordinated nitrate anions lead to layers parallel to (100).

In the title compound, [Cu(C(2)O(4))(C(13)H(20)N(4))(H(2)O)]·2H(2)O, the Cu(II) atom exhibits a distorted square-pyramidal geometry with the two N atoms of the imidazole ligand and the two O atoms of the oxalate ligand forming the basal plane, while the O atom of the coordinated water mol-ecule is in an apical position. The Cu(II) atom is shifted 0.232 (2) Å out of the basal plane toward the water mol-ecule. The asymmetric unit is completed by two solvent water mol-ecules. These water mol-ecules participate in the formation of an intricate three-dimensionnal network of hydrogen bonds involving the coordinated water mol-ecule and the NH groups.