Remodeling the Electronic Structure of Metallic Nickel and Ruthenium via Alloying in a Molecular Template for Sustainable Hydrogen Evolution.

The reasonably constructed high-performance electrocatalyst is crucial to achieve sustainable electrocatalytic water splitting. Alloying is a prospective approach to effectively boost the activity of metal electrocatalysts. However, it is a difficult subject for the controllable synthesis of small alloying nanostructures with high dispersion and robustness, preventing further application of alloy catalysts. Herein, we propose a well-defined molecular template to fabricate a highly dispersed NiRu alloy with ultrasmall size. The catalyst presents superior alkaline hydrogen evolution reaction (HER) performance featuring an overpotential as low as 20.6 ± 0.9 mV at 10 mA·cm-2. Particularly, it can work steadily for long periods of time at industrial-grade current densities of 0.5 and 1.0 A·cm-2 merely demanding low overpotentials of 65.7 ± 2.1 and 127.3 ± 4.3 mV, respectively. Spectral experiments and theoretical calculations revealed that alloying can change the d-band center of both Ni and Ru by remodeling the electron distribution and then optimizing the adsorption of intermediates to decrease the water dissociation energy barrier. Our research not only demonstrates the tremendous potential of molecular templates in architecting highly active ultrafine nanoalloy but also deepens the understanding of water electrolysis mechanism on alloy catalysts.

A confinement-regulated (H3C-NH3)+ ion as a smallest dual-wheel rotator showing bisected rotation dynamics.

On the basis of variable-temperature single-crystal X-ray diffraction, rotational energy barrier analysis, variable-temperature/frequency dielectric response, and molecular dynamics simulations, here we report a new crystalline supramolecular rotor (CH3NH3)(18-crown-6)[CuCl3], in which the (H3C-NH3)+ ion functions as a smallest dual-wheel rotator showing bisected rotation dynamics, while the host 18-crown-6 macrocycle behaves as a stator that is not strictly stationary. This study also provides a helpful insight into the dynamics of ubiquitous -CH3/-NH3 groups confined in organic or organic-inorganic hybrid solids.

Molecular rotators anchored on a rod-like anionic coordination polymer adhered by charge-assisted hydrogen bonds.

On the basis of variable-temperature single-crystal X-ray diffraction, variable-temperature/frequency dielectric analysis, variable-temperature solid-state nuclear magnetic resonance spectroscopy, and molecular dynamics simulations, here we present a new model of crystalline supramolecular rotor (i-PrNHMe2)[CdBr3], where a conformationally flexible near-spherical (i-PrNHMe2)+ cation functions as a rotator and a rod-like anionic coordination polymer {[CdBr3]-}∞ acts as the stator, and the adhesion of them is realized by charge-assisted hydrogen bonds.

Optimizing the Spatial Density of Single Co Sites via Molecular Spacing for Facilitating Sustainable Water Oxidation.

Advances in single-atom (-site) catalysts (SACs) provide a new solution of atomic economy and accuracy for designing efficient electrocatalysts. In addition to a precise local coordination environment, controllable spatial active structure and tolerance under harsh operating conditions remain great challenges in the development of SACs. Here, we show a series of molecule-spaced SACs (msSACs) using different acid anhydrides to regulate the spatial density of discrete metal phthalocyanines with single Co sites, which significantly improve the effective active-site numbers and mass transfer, enabling one of the msSACs connected by pyromellitic dianhydride to exhibit an outstanding mass activity of (1.63 ± 0.01) × 105 A·g-1 and TOFbulk of 27.66 ± 1.59 s-1 at 1.58 V (vs RHE) and long-term durability at an ultrahigh current density of 2.0 A·cm-2 under industrial conditions for oxygen evolution reaction. This study demonstrates that the accessible spatial density of single atom sites can be another important parameter to enhance the overall performance of catalysts.

Temperature-Tuned Variable Confined Space for Modulating Dipolar Polarization of a Disc-Shaped Ammonium Ion.

Free accessible confined space and loose interaction are crucial for most solid-state ionic motions. Here, by using a near-spherical anion and a disc-shaped ammonium as two distinct but rigid building blocks, we report a new ionic crystal, (HMIm)3[La(NO3)6] (HMIm = 1-methyl-1H-imidazol-3-ium), in which the different confined spaces of three (HMIm)+ ions are fine-tuned over a broad temperature range. This effect can be utilized to modulate the dipolar polarization across a wide temperature/frequency range. Additionally, small-scale substitution of (HMIm)+ by its isomer of almost identical shape/size affords molecular solid solutions, which can further tune the dipolar polarization by varying the doping ratio. It is revealed that the differences in dipole moment and hydrogen bond rather than that of shape/size lead to a distorted crystalline environment for these solid solutions. Overall, we provide an exceptional model for understanding and regulating the dipole motion of polar aromatic molecules/ions in a crystalline environment.

Molecule-Enhanced Electrocatalysis of Sustainable Oxygen Evolution Using Organoselenium Functionalized Metal-Organic Nanosheets.

Remolding the reactivity of metal active sites is critical to facilitate renewable electricity-powered water electrolysis. Doping heteroatoms, such as Se, into a metal crystal lattice has been considered an effective approach, yet usually suffers from loss of functional heteroatoms during harsh electrocatalytic conditions, thus leading to the gradual inactivation of the catalysts. Here, we report a new heteroatom-containing molecule-enhanced strategy toward sustainable oxygen evolution improvement. An organoselenium ligand, bis(3,5-dimethyl-1H-pyrazol-4-yl)selenide containing robust C-Se-C covalent bonds equipped in the precatalyst of ultrathin metal-organic nanosheets Co-SeMON, is revealed to significantly enhance the catalytic mass activity of the cobalt site by 25 times, as well as extend the catalyst operation time in alkaline conditions by 1 or 2 orders of magnitude compared with these reported metal selenides. A combination of various in situ/ex situ spectroscopic techniques, ab initio molecular dynamics, and density functional theory calculations unveiled the organoselenium intensified mechanism, in which the nonclassical bonding of Se to O-containing intermediates endows adsorption-energy regulation beyond the conventional scaling relationship. Our results showcase the great potential of molecule-enhanced catalysts for highly efficient and economical water oxidation.

Insights into the Molecular Dynamics of Quasi-Spherical (Chloromethyl)triethylammonium Confined in a Weakly Bound Ionic Cocrystal.

Here, we report a weakly bound ionic cocrystal, (Et3NCH2Cl)2[ZnCl4], which undergoes a reversible structural phase transition owing to the switched molecular dynamics of the quasi-spherical (Et3NCH2Cl)+ cation from static to dynamic. Interestingly, a unique rolling and moving mechanism is uncovered for such a cation in the high-temperature phase, where its two methylene groups exhibit different kinetic energy barriers. This study provides a meaningful insight into the solid-state molecular dynamics of large-size quasi-spherical molecules that contain both a rigid core and flexible shell.

Solid solutions of flexible host-guest supramolecules for tuning molecular motion and phase transitions.

By utilizing a supramolecular complex rather than an individual molecule as a deformable and elastic substitutional component, we put forward a solid-solution strategy and demonstrate an example of how two related yet non-isostructural crystalline host-guest compounds can form molecular solid solutions. Interestingly, such a strategy can effectively and continuously modulate the molecular motion and phase transition in them, as revealed by the variable-temperature/frequency dielectric responses.

Electrochemically Controlled Synthesis of Ultrathin Nickel Hydroxide Nanosheets for Electrocatalytic Oxygen Evolution.

The development of oxygen evolution reaction (OER) catalysts with high activity and high stability through convenient and economical methods is greatly important for the promotion of hydrogen energy based on electrolysis technology. Herein, by using an unconventional high electrodeposition potential, novel petal-like clusters constructed by cross-linking ultrathin nickel hydroxide nanosheets were controllably synthesized on nickel foam (or copper foam or carbon cloth) and the effect of electrodeposition conditions on their OER performance was carefully explored. Due to the abundant catalytically active sites, promoting electron conduction/mass transmission from the specific micro-nano structure, as well as the ultrasmall thickness of ∼3.0 nm, the optimized α-Ni(OH)2/NF self-supporting electrode exhibits excellent electrocatalytic performance for OER, merely requiring low overpotentials of 192 and 240 mV to yield current densities of 10 and 100 mA cm-2 in 1.0 M KOH, respectively, which surpassed those of all of the reported nickel hydroxide/oxides and the benchmark RuO2. Moreover, α-Ni(OH)2/NF can drive the high-current density (500-1000 mA cm-2) OER at low overpotentials, meeting the requirements of potential industrial applications.

Molecule-based nonlinear optical switch with highly tunable on-off temperature using a dual solid solution approach.

Nonlinear optical switches that reversibly convert between on/off states by thermal stimuli are promising for applications in the fields of photoelectronics and photonics. Currently one main drawback for practical application lies in the control of their switch temperature, especially for the temperature range near room temperature. By mixed melting treatment, here we describe an alloy-like nonlinear optical switch with tunable switch temperature via a dual solid solution approach within the coordination polymer system. We initially prepare a coordination polymer (i-PrNHMe2)[Cd(SCN)3], which functions as a high-contrast thermoresponsive nonlinear optical switch originating from a phase transition at around 328 K. Furthermore, by taking advantage of a synergistic dual solid solution effect, the melt mixing of it with its analogue (MeNHEt2)[Cd(SCN)3], which features an unequal anionic chain templated by an isomeric ammonium, can afford coordination polymer solid solutions with switch temperatures that are tunable in a range of 273-328 K merely by varying the component ratio.

Molecular Dynamics, Phase Transition and Frequency-Tuned Dielectric Switch of an Ionic Co-Crystal.

Dielectric switches that can be converted between high and low dielectric states by thermal stimuli have attracted much interest owing to their many potential applications. Currently one main drawback for practical application lies in the non-tunability of their switch temperatures (TS ). We report here an ionic co-crystal (Me3 NH)4 [Ni(NCS)6 ] that contains a multiply rotatable Me3 NH+ ion and a solely rotatable one due to a more spacious supramolecular cage for the former one. This compound undergoes an isostructural order-disorder phase transition and it can function as a frequency-tuned dielectric switch with highly adjustable TS , which is further revealed by the variable-temperature structure analyses and molecular dynamics simulations. In addition, the distinct arrangements and molecular dynamics of two coexisting Me3 NH+ ions confined in different lattice spaces as well as the notable offset effect on the promoting/hindering of dipolar reorientation after dielectric transition provide a rarely observed but fairly good model for understanding and modulating the dipole motion in crystalline environment.

Matching of Host-Guest Symmetry/Orientation and Molecular Dynamics in Two Double Perovskite-Like Azido Coordination Polymers.

Two new double perovskite-like azido coordination polymers with trimethylammonium as the guest cation, namely, (Me3NH)2[CrNa(N3)6] and (Me3NH)2[CrK(N3)6], have been prepared. The molecular dynamics for both compounds are investigated and are clearly uncovered by the first-principles molecular dynamics simulation and the significant dielectric relaxation. Structural analyses of these compounds in combination with their analogue (Me3NH)[Mn(N3)3] reveal that the guest trimethylammonium has flexible structural adaptability, especially with a variety of disordered distributions, to match the different symmetries of varied metal-azido frameworks. Interestingly, the replacement of the divalent metal ion by mixed monovalent/trivalent metal ions can change the symmetry, shape, and charge distribution of the host cage unit; thus it may influence and regulate the arrangement of the guest inclusion and its molecular dynamics as well as the structural phase transition.

Crystalline Supramolecular Gyroscope with a Water Molecule as an Ultrasmall Polar Rotator Modulated by Charge-Assisted Hydrogen Bonds.

A new strategy for the construction of crystalline molecular rotors is presented. The combination of a conformation-modifiable macrocyclic host and two cooperative guests affords one supramolecular gyroscope-like compound, (t-BuNH3)(18-crown-6)[ZnCl3(H2O)], in which the coordinated water molecule functions as an ultrasmall polar rotator, revealed by its significant dielectric relaxation and the molecular dynamics simulations. In addition, such a compound can reversibly undergo a polar-to-polar phase transition triggered by the changed conformation of the 18-crown-6 host, leading to a switchable on/off rotation of water molecule, well controlled by strength and direction of charge-assisted hydrogen bonds.

Plastic Crystals with Polar Halochromate Anion: Thermosensitive Dielectrics Based upon Plastic Transition and Dipole Rotation.

Plastic crystals functioning with rotatable components offer new opportunities in areas such as modern optoelectronic materials. Here, by taking advantage of controllable rotation of the polar component within the ion-pair plastic-crystal system, we present two such crystals, namely, (Et4N)(CrO3X) (X = Cl or Br), which are unusual examples exhibiting two-staged thermosensitive dielectric responses above room temperature. The frequency-dependent response in the first stage is due to the structural phase transitions, whereas that in the second stage is induced by dynamic rotation of the polar halochromate anions in their NaCl-type plastic-crystal phases. The intrinsic mechanisms were also explicated by molecular dynamics simulations, providing a direct insight into the dynamic characteristics of these two compounds. These studies show that ionic plastic crystals functioning with polar groups are an attractive candidate as sensitive thermoresponsive dielectric materials.

3D chiral and 2D achiral cobalt(ii) compounds constructed from a 4-(benzimidazole-1-yl)benzoic ligand exhibiting field-induced single-ion-magnet-type slow magnetic relaxation.

Organizing magnetically isolated 3d transition metal ions, which behave as single-ion magnet (SIM) units, in a coordination network is a promising approach to design novel single-molecule magnets (SMMs). Herein 3D chiral and 2D achiral cobalt(ii) coordination compounds based on single metal nodes with a 4-(benzimidazole-1-yl)benzoic acid (Hbmzbc) ligand, namely, [Co(bmzbc)2(1,2-etdio)]n () (1,2-etdio = 1,2-ethanediol) and [Co(bmzbc)2(Hbmzbc)]n (), have been synthesized and structurally characterized. The 3D chiral structure with 2-fold interpenetrating qtz topological nets consisting of totally achiral components was obtained via spontaneous resolution, while the achiral structure is a 2D (4,4) net. In both structures, individual cobalt(ii) ions are spatially well separated by the long organic ligands in the well-defined networks. Magnetic measurements on and showed field-induced slow magnetic relaxation resulting from single-ion anisotropy of the individual Co(ii) ions. Analysis of the dynamic ac susceptibilities with the Arrhenius law afforded an anisotropy energy barrier of 16.8(3) and 31.3(2) K under a 2 kOe static magnetic field for and , respectively. The distinct coordination environments of the Co(ii) ions in and lead to the different anisotropic energy barriers.

Anion Effects on Lanthanide(III) Tetrazole-1-acetate Dinuclear Complexes Showing Slow Magnetic Relaxation and Photofluorescent Emission.

Three types of lanthanide complexes based on the tetrazole-1-acetic acid ligand and the 2,2'-bipyridine coligand were prepared and characterized by single-crystal X-ray diffraction, IR spectroscopy, and elemental analyses; the formulas of these complexes are [Ln2(1-tza)4(NO3)2(2,2'-bipy)2] (Ln = Sm (1), Eu (2), Gd (3), Tb (4), Dy (5)), [Dy2(1-tza)4Cl2(2,2'-bipy)2] (6), and [Yb2(1-tza)4(NO3)2(2,2'-bipy)2] (7) (1-tza = tetrazole-1-acetate and 2,2'-bipy = 2,2'-bipyridine). They are dinuclear complexes possessing similar structures but different lanthanide(III) ion coordination geometries because of the distinction of peripheral anions (such as NO3(-) and Cl(-)) and the effect of lanthanide contraction. The variable-temperature magnetic susceptibilities of 1-6 were measured. Both Dy(III) complexes (5 and 6) display field-induced single-molecule magnet behaviors. Ab initio calculations revealed that the Dy(III) complex 6 possesses a more anisotropic Dy(III) ion in comparison to that in 5. The room-temperature photoluminescence spectra of Sm(III) (1), Eu(III) (2), Tb(III) (4), and Dy(III) (5 and 6) complexes exhibit strong characteristic emissions in the visible region, whereas the Yb(III) (7) complex shows near-infrared (NIR) luminescence.

Insight into the molecular dynamics of guest cations confined in deformable azido coordination frameworks.

The molecular dynamics of encapsulated cations within perovskite-like coordination polymers [(CH3)3NH][M(N3)3] (M = Mn, Cd) are investigated, which are well controlled by the confined space of a deformable azido framework. The Mn-based compound provides a rare example that features an unvaried/varied rotational energy barrier during its two different structural phase transitions.

Switchable guest molecular dynamics in a perovskite-like coordination polymer toward sensitive thermoresponsive dielectric materials.

A new perovskite-like coordination polymer [(CH3)2NH2][Cd(N3)3] is reported which undergoes a reversible ferroelastic phase transition. This transition is due to varied modes of motion of the [(CH3)2NH2](+) guest accompanied by a synergistic deformation of the [Cd(N3)3](-) framework. The unusual two-staged switchable dielectric relaxation reveals the molecular dynamics of the polar cation guest, which are well controlled by the variable confined space of the host framework. As the material switches from the ferroelastic phase to the paraelastic phase, a remarkable increase of the rotational energy barrier is detected. As a result, upon heating at low temperature, this compound shows a notable change from a low to a high dielectric state in the ferroelastic phase. This thermoresponsive host-guest system may serve as a model compound for the development of sensitive thermoresponsive dielectric materials and may be key to understanding and modulating molecular/ionic dynamics of guest molecules in confined space.

An amine-functionalized metal-organic framework as a sensing platform for DNA detection.

An amine-functionalized metal-organic framework (MOF) has been employed as an effective fluorescent sensing platform for DNA detection and is capable of distinguishing complementary and mismatched target sequences with high sensitivity and selectivity.

Restraining the motion of a ligand for modulating the structural phase transition in two isomorphic polar coordination polymers.

A structural phase transition induced by ligand motion was found in a new polar coordination polymer: [Cu(NCS)2(4-APy)2]n (4-APy = 4-aminopyridine). Restraining such motion in an isomorphic compound [Cu(NCS)2(4-MeAPy)2]n (4-MeAPy = 4-methylaminopyridine) results in distinct phase transition behaviour. These findings provide a new clue for modulating phase transition behaviour in known materials.