Two-dimensional Hydrogen-bonded Network Research Articles

Proton Conduction in Chiral Molecular Assemblies of Azolium-Camphorsulfonate Salts.

Chiral molecular assemblies have attracted considerable attention because of their interesting physical properties, such as spin-selective electron transport. Cation-anion salts of three azolium cations, imidazolium (HIm+), triazolium (HTrz+), and thiazolium (HThz+), in combination with a chiral camphorsulfonate (1S-CS-) and their racemic compounds (rac-CS-) were prepared and compared in terms of phase transitions, crystal structures, dynamics of constituent molecules, dielectric responses, and proton conductivities. The cation-anion crystals containing HIm+ showed no significant difference in proton conductivity between the homochiral and racemic crystals, whereas the HTrz+-containing crystals showed higher proton conductivity and lower activation energy in the homochiral form than in the racemic form. A two-dimensional hydrogen-bonding network consisting of HTrz+ and -SO3- groups and similar in-plane rotational motion was observed in both crystals; however, the HTrz+ cation in the homochiral crystal exhibited the rotational motion modulated with translational motion, whereas the HTrz+ cation in the racemic crystal exhibited almost steady in-plane rotational motion. The different motional degrees of freedom were confirmed by crystal structure analyses and temperature- and frequency-dependent dielectric constants. In contrast, steady in-plane rotational motion with the thermally activated fluctuating motion of CS- was observed both in homochiral and racemic crystals containing HIm+, which averaged the motional space of protons resulting in similar dielectric responses and proton conductivities. The control of motional degrees of freedom in homochiral crystals affects the proton conductivity and is useful for the design of molecular proton conductors.

Elucidating the water-anatase TiO2(101) interface structure using infrared signatures and molecular dynamics.

The structure and dynamics of water on solid surfaces critically affect the chemistry of materials in ambient and aqueous environments. Here, we investigate the hydrogen bonding network of water adsorbed on the majority (101) surface of anatase TiO2, a widely used photocatalyst, using polarization- and azimuth-resolved infrared spectroscopy combined with neural network potential molecular dynamics simulations. Our results show that one monolayer of water saturates the undercoordinated titanium (Ti5c) sites, forming one-dimensional chains of molecule hydrogen bonded to surface undercoordinated bridging oxygen (O2c) atoms. As the coverage increases, water adsorption on O2c sites leads to significant restructuring of the water monolayer and the formation of a two-dimensional hydrogen bond network characterized by tightly bound pairs of water molecules on adjacent Ti5c and O2c sites. This structural motif likely persists at ambient conditions, influencing the reactions occurring there. The results reported here provide critical details of the structure of the water-anatase (101) interface that were previously hypothesized but unconfirmed experimentally.

Hydrogen-bonded nickel(II)-organosulfonate framework: Thermal expansion behavior, proton conduction, and magnetic properties

Metalo Hydrogen-bonded organic frameworks are emerging supramolecular platforms for designing functional molecular materials. Herein, we reported the supramolecular structure, thermal, magnetic, and proton conduction properties of a hydrogen-bonded nickel(II)-organosulfonate framework, [Ni(H2O)6][NPS]2 (NiHOF, HNPS = naphthalene-2-sulphonic acid). Single-crystal X-ray diffraction studies reveal a two-dimensional hydrogen-bonded network sustained by multiple and charge-assisted OH···O H bonds between hexaaquanickel(II) cations and organosulfonate anions. Additionally, continuous ca. 0.47 × 0.70 nm2 windows were formed within the framework. The thermal stability of the NiHOF was confirmed by thermal gravimetric analysis and variable temperature single-crystal and powder X-ray diffraction patterns. N2 sorption isotherms suggest an ultramicroporous supramolecular framework of NiHOF with permanent porosity. The anisotropic positive thermal expansion behavior of NiHOF was evidenced by the dynamic crystallography experiments. Magnetic measurements indicate easy-axis magnetic anisotropy (D = -10.5 cm−1) of the NiHOF while no slow magnetic relaxation behavior. Electrochemical impedance spectroscopy indicates the temperature and humidity dependence of conductivities of NiHOF. At 50 °C and 70% relative humidity, the conductivity is 1.13 × 10−4 S·cm−1, revealing a supramolecular proton conductor of NiHOF. This work provides a potential way for designing novel thermal, magnetic, and electrical molecular materials through the supramolecular assembly of inorganic and organosulfonate synthons.

Anisotropic and Finite Effects on Intermolecular Vibration and Relaxation Dynamics: Low-Frequency Raman Spectroscopy of Water Film and Droplet on Graphene by Molecular Dynamics Simulations.

The structural and dynamical properties of water can be greatly altered by the anisotropic interfacial environment. Here, we study the intermolecular vibration and relaxation dynamics of a water film and a water droplet on a graphene surface based on low-frequency Raman spectra calculated from molecular dynamics simulations. The calculated Raman spectra of the interfacial water systems show a weakened libration peak and an enhanced intermolecular hydrogen bond (HB) stretching peak compared to the spectrum of bulk water, which are attributed to softened orientation motion. We also find that the collective polarizability relaxation in the droplet is much slower than that in the film and bulk, which is completely different from the collective dipole relaxation. The slow relaxation is due to a positive correlation between the induced polarizabilities of distinct molecules caused by the global and anisotropic structural fluctuations of the water droplet. Furthermore, we find that the two-dimensional HB network by the orientation-ordered interfacial water molecules leads to different intermolecular vibration dynamics between the parallel and perpendicular components. The present theoretical study demonstrates that low-frequency Raman spectroscopy can reveal the anisotropic and finite effects on the intermolecular dynamics of the water film and droplet.

Supramolecular Organization in Salts of Riluzole with Dihydroxybenzoic Acids—The Key Role of the Mutual Arrangement of OH Groups

Intermolecular interactions, in particular hydrogen bonds, play a key role in crystal engineering. The ability to form hydrogen bonds of various types and strengths causes competition between supramolecular synthons in pharmaceutical multicomponent crystals. In this work, we investigate the influence of positional isomerism on the packing arrangements and the network of hydrogen bonds in multicomponent crystals of the drug riluzole with hydroxyl derivatives of salicylic acid. The supramolecular organization of the riluzole salt containing 2,6-dihydroxybenzoic acid differs from that of the solid forms with 2,4- and 2,5-dihydroxybenzoic acids. Because the second OH group is not at position 6 in the latter crystals, intermolecular charge-assisted hydrogen bonds are formed. According to periodic DFT calculations, the enthalpy of these H-bonds exceeds 30 kJ·mol-1. The positional isomerism appears to have little effect on the enthalpy of the primary supramolecular synthon (65-70 kJ·mol-1), but it does result in the formation of a two-dimensional network of hydrogen bonds and an increase in the overall lattice energy. According to the results of the present study, 2,6-dihydroxybenzoic acid can be treated as a promising counterion for the design of pharmaceutical multicomponent crystals.

Anisotropy and Hybrid Heterosurface-Modulated Two-Dimensional Hydrogen Bond Network of Water

We report the structure and dynamics of layered water structure near a bilayer heterosurface using classical molecular dynamics simulations and network graph theory. The heterosurfaces of our choice are technologically essential and well-studied hexagonal boron nitride (h-BN) and graphitic carbon nitride (g-C3N4). Starting with the water density distribution profile, we have studied different hydrogen bondings (HBs) associated with distance and angle distributions and correlated them with the HB count, followed by the investigations of dynamic properties. We realize the oddity while corresponding to the tetrahedral order parameter (TOP), HB donor/acceptor count, and HB lifetime. A quantitative gap is observed between the TOP and HB counts, and we perceive another structural factor playing a significant role. We observe a 2D sheetlike arrangement of hydrogen-bonded water molecules, namely, 2D-HB, in the interfacial layer instead of 3D tetrahedral arrangements. 2D-HB qualitatively acts as a key descriptor of the hydrophobicity of the interface. The probability of higher TOP among the interfacial layer water molecules is less for h-BN compared to g-C3N4. However, the per-water HBs for both the heterosurfaces remain indistinguishable, implying the existence of another significant physical factor related to HB. Hence, 2D-HB serves as a deciding factor. In the case of h-BN, water molecules in the first layer form extended 2D sheets compared to the second and bulk, which is not a scenario for g-C3N4. Following the network graph theory, we calculated the temporal evolution of the maximum number of water molecules connected in a single network. The layer 1 water molecules have slower orientational dynamics, higher HB lifetime, and consequently slower translational diffusion than layer 2 and bulk water molecules. The experimental studies suggested that the contact angle of water on h-BN can vary from 61.4 to 85.8°, higher than that of g-C3N4, depending on the surface stacking, support material, and exposure to air, which effectively makes h-BN more hydrophobic compared to g-C3N4. The interfacial water molecules have a smaller HB lifetime and a faster diffusion coefficient than g-C3N4. The HB lifetime of water molecules in bulk is less than that in the interface, irrespective of the surface. A slower reorientation lifetime, that is, 2.69 ps, for g-C3N4 interfacial water molecules is observed versus 2.20 ps for h-BN. Our results agree with the experimental observations and can help to understand the hydrophobicity of other relevant materials.

Physicochemical aspects and comparative analysis of Voxelotor and its salt and cocrystal

Voxelotor (VOX) is a BCS (Biopharmaceutical classification system) Class II drug (poor solubility and high permeability) and is issued for the treatment of sickle cell disease. The VOX free base, VOX-HCl salt and succinic acid (VOX-SC) cocrystals were crystallized and their crystal structures were determined by the Single Crystal X-ray diffraction technique (SCXRD). Further, solid-state characterization techniques such as Nuclear magnetic resonance (NMR) and Fourier transform Infra-red spectroscopy(FT-IR) were carried out. In all three structures, the VOX molecules exhibit an intramolecular S(6)-motif formed by O-H⋅⋅⋅O hydrogen bond. In VOX free base, only weak C-H⋅⋅⋅O, C-H⋅⋅⋅π and π⋅⋅⋅π interactions were observed, which lead to the formation of two-dimensional hydrogen-bonded sheets. In VOX-HCl salt, N-H⋅⋅⋅Cl hydrogen bond along with the C-H⋅⋅⋅π and π⋅⋅⋅π interactions form a discrete dimeric unit. In VOX-SC cocrystal, the VOX and SC molecules were connected through N-H⋅⋅⋅O, O-H⋅⋅⋅O and C-H⋅⋅⋅O interactions and generate a two-dimensional hydrogen-bonded network. Thermal analysis of VOX-SC cocrystal resulted in melting points intermediate to that of API and coformer, while VOX-HCl salt yielded a higher melting point than the parent VOX. Both VOX-HCl and VOX-SC cocrystal showed better solubility compared to VOX free base. The stress analysis revealed that in VOX-SC cocrystal, no physical transformations of solid-phase was observed. Enhancement in solubility and stability was observed in the obtained VOX-SC cocrystal in comparison to the free base.

Low-temperature phase transition and high-pressure phase stability of 1H-pyrazole-1-carboxamidine nitrate

The phase transition observed in a temperature-dependent experiment at 174 K is unachievable under high-pressure conditions. Negative thermal expansion for phase (II) and negative compressibility for phase (I) were observed. A new salt of 1H-pyrazole-1-carboxamidine, (HPyCA)NO3, for guanylation reaction was obtained in a crystalline form. The compound crystallizes in monoclinic space group P21/c and a phase transition at 174 K to triclinic modification P 1 was found. An unusual increase of the unit-cell volume was observed just after transition. Although the volume decreases upon cooling, it remains higher down to 160 K in comparison to the unit-cell volume of phase (I). The mechanism of the phase transition is connected with a minor movement of the nitrate anions. The triclinic phase was unreachable at room-temperature high-pressure conditions up to 1.27 GPa. On further compression, delamination of the crystal was observed. Phase (I) exhibits negative linear compressibility, whereas abnormal behaviour of the b unit-cell parameter upon cooling was observed, indicating negative thermal linear expansion. The unusual nature of the compound is associated with the two-dimensional hydrogen-bonding network, which is less susceptible to deformation than stacking interactions connecting the layers of hydrogen bonds. Infrared spectroscopy and differential scanning calorimetry measurements were used to investigate the changes of intermolecular interactions during the phase transition.

Interplay between Local Structure and Nuclear Dynamics in Tungstic Acid: A Neutron Scattering Study

We provide an exhaustive characterization of structural properties and nuclear dynamics in tungstic acid (WO3·H2O). To this end, we employ neutron and X-ray diffraction (ND and XRD) combined with inelastic neutron scattering (INS) and neutron Compton scattering (NCS) experiments, and we corroborate the analysis with extensive ab initio modeling. The first step in our analysis is the elucidation of the crystal structure based on the refinement of low-temperature powder ND data, extending the knowledge gained from XRD analysis of a mineral specimen of tungstite. These results are confronted with low-temperature INS experiments and zero-temperature phonon calculations. The analysis reveals an inconsistency in the definition of the structure of confined water with respect to crystallographic data, also showing a concomitant failure of the phonon calculations due to a strongly anharmonic confining potential. Extending the computational route toward ab initio MD (AIMD) simulations allows us to probe different structural configurations and provides an improved description of the vibrational dynamics as compared to high-resolution INS experiments, nevertheless, requiring the use of effective classical temperatures. The analysis of both INS and the NCS data reveals a remarkable similarity to the nuclear dynamics earlier reported for water confined in single-wall carbon nanotubes (SWNT), which has been qualitatively described as a new phase of ice. Our analysis reveals a strong two-dimensional hydrogen-bonding network, similar to the shell model for water in SWNT. The reported NCS data show narrowing of the hydrogen momentum distribution with respect to the reference ab initio calculations, indicating a great deal of conformational freedom due to spatial delocalization of protons in the ground state of the system, a clear signature of the quantum character of the nuclei.

Molecular Fingerprints of Hydrophobicity at Aqueous Interfaces from Theory and Vibrational Spectroscopies

Hydrophobicity/hydrophilicity of aqueous interfaces at the molecular level results from a subtle balance in the water–water and water–surface interactions. This is characterized here via density functional theory–molecular dynamics (DFT-MD) coupled with vibrational sum frequency generation (SFG) and THz-IR absorption spectroscopies. We show that water at the interface with a series of weakly interacting materials is organized into a two-dimensional hydrogen-bonded network (2D-HB-network), which is also found above some macroscopically hydrophilic silica and alumina surfaces. These results are rationalized through a descriptor that measures the number of “vertical” and “horizontal” hydrogen bonds formed by interfacial water, quantifying the competition between water–surface and water–water interactions. The 2D-HB-network is directly revealed by THz-IR absorption spectroscopy, while the competition of water–water and water–surface interactions is quantified from SFG markers. The combination of SFG and THz-IR spectroscopies is thus found to be a compelling tool to characterize the finest details of molecular hydrophobicity at aqueous interfaces.

Polymorphs of phenazine hexacyanoferrate(II) hydrate: supramolecular isomerism in a 2D hydrogen-bonded network.

The crystal structures of two polymorphs of a phenazine hexacyanoferrate(II) salt/cocrystal, with the formula (Hphen)3[H2Fe(CN)6][H3Fe(CN)6]·2(phen)·2H2O, are reported. The polymorphs are comprised of (Hphen)2[H2Fe(CN)6] trimers and (Hphen)[(phen)2(H2O)2][H3Fe(CN)6] hexamers connected into two-dimensional (2D) hydrogen-bonded networks through strong hydrogen bonds between the [H2Fe(CN)6]2- and [H3Fe(CN)6]- anions. The layers are further connected by hydrogen bonds, as well as through π-π stacking of phenazine moieties. Aside from the identical 2D hydrogen-bonded networks, the two polymorphs share phenazine stacks comprising both protonated and neutral phenazine molecules. On the other hand, the polymorphs differ in the conformation, placement and orientation of the hydrogen-bonded trimers and hexamers within the hydrogen-bonded networks, which leads to different packing of the hydrogen-bonded layers, as well as to different hydrogen bonding between the layers. Thus, aside from an exceptional number of symmetry-independent units (nine in total), these two polymorphs show how robust structural motifs, such as charge-assisted hydrogen bonding or π-stacking, allow for different arrangements of the supramolecular units, resulting in polymorphism.

Pressure induced topochemical polymerization of solid acrylamide facilitated by anisotropic response of the hydrogen bond network.

The pressure induced polymerization of molecular solids is an appealing route to obtain pure, crystalline polymers without the need for radical initiators. Here, we report a detailed density functional theory (DFT) study of the structural and chemical changes that occur in defect free solid acrylamide, a hydrogen bonded crystal, when it is subjected to hydrostatic pressures. While our calculations are able to reproduce experimentally measured pressure dependent spectroscopic features in the 0-20 GPa range, our atomistic analysis predicts polymerization in acrylamide at a pressure of ∼23 GPa at 0 K albeit through large enthalpy barriers. Interestingly, we find that the two-dimensional hydrogen bond network in acrylamide templates topochemical polymerization by aligning the atoms through an anisotropic response at low pressures. This results not only in conventional C-C, but also unusual C-O polymeric linkages, as well as a new hydrogen bonded framework, with both N-HO and C-HO bonds. Using a simple model for thermal effects, we also show that at 300 K, higher pressures significantly accelerate the transformation into polymers by lowering the barrier. Thus, application of pressure offers an alternative route for topochemical polymerization when higher temperatures are undesirable.

Quasi-One-Dimensional Free-Electron-Like States Selected by Intermolecular Hydrogen Bonds at the Glycine/Cu(100) Interface* *Supported by the National Natural Science Foundation of China (Grant Nos. 11622437, 11804247, 61674171, and 11974422), the Fundamental Research Funds for the Central Universities of China and the Research Funds of Renmin University of China (Grant Nos. 19XNQ025 and 19XNH066), and the Strategic Priority Research Program of Chinese

We carry out ab initio density functional theory calculations to study manipulation of electronic structures of self-assembled molecular nanostructures on metal surfaces by investigating the geometric and electronic properties of glycine molecules on Cu(100). It is shown that a glycine monolayer on Cu(100) forms a two-dimensional hydrogen-bonding network between the carboxyl and amino groups of glycine using a first principles atomistic calculation on the basis of a recently found structure. This network includes at least two hydrogen-bonding chains oriented roughly perpendicular to each other. Through molecule–metal electronic hybridization, these two chains selectively hybridized with the two isotropic degenerate Cu(100) surface states, leading to two anisotropic quasi-one-dimensional surface states. Electrons occupying these two states can near-freely move from a molecule to its adjacent molecules directly through the intermolecular hydrogen bonds, rather than mediated by the substrate. This results in the experimentally observed anisotropic free-electron-like behavior. Our results suggest that hydrogen-bonding chains are likely candidates for charge conductors.

A Facile Approach of Thin Film Coating Consisted of Hydrophobic Titanium Dioxide over Polypropylene Membrane for Membrane Distillation

In this work, the hydrophobic modification of TiO2 nanoparticles (HTiO2) was carried out by reacting with dodecylphosphonic acid (DDPA) and hexylamine solution. A facile approach of the self-assembly technique was used for the coating of hydrophobic HTiO2 layer over the microporous polypropylene (PP) membrane. The self-assembled layer was formed between the interface of trimesoyl chloride (TMC) (in hexane) and trimethylamine (in water) solutions. The high porosity for the coated membranes ascribed to the selfassembled trimesic acid (TMA) layer and its potential to generate open and loosely packed, two-dimensional hydrogen-bond networks on the membrane surface. The dispersion of HTiO2 was accomplished in the TMC in hexane leading hydrophobic and porous surfaces than the neat PP membrane. The initial average pore size of the PP membrane was reduced from 0.4 μm to 0.2 μm with a coating of 2.0 wt% of HTiO2. The new membranes showed high reliability, high rejection, and water flux during the real seawater desalination tested in direct contact membrane distillation (DCMD) configuration. The maximum transmembrane permeate flux of 45.4 kg/m2h with >98% salt rejection was obtained for the coating layer with 2.0 wt% HTiO2 at 80oC demonstrating the future potential application towards seawater desalination.

The first coordination compound of deprotonated 2-bromo-nicotinic acid: crystal structure of a dinuclear paddle-wheel copper(II) complex.

A copper(II) dimer with the deprotonated anion of 2-bromo-nicotinic acid (2-BrnicH), namely, tetrakis(μ-2-bromonicotinato-κ2 O:O')bis[aquacopper(-II)](Cu-Cu), [Cu2(H2O)2(C6H3BrNO2)4] or [Cu2(H2O)2(2-Brnic)4], (1), was prepared by the reaction of copper(II) chloride dihydrate and 2-bromo-nicotinic acid in water. The copper(II) ion in 1 has a distorted square-pyramidal coordination environment, achieved by four carboxyl-ate O atoms in the basal plane and the water mol-ecule in the apical position. The pair of symmetry-related copper(II) ions are connected into a centrosymmetric paddle-wheel dinuclear cluster [Cu⋯Cu = 2.6470 (11) Å] via four O,O'-bridging 2-bromo-nicotinate ligands in the syn-syn coordination mode. In the extended structure of 1, the cluster mol-ecules are assembled into an infinite two-dimensional hydrogen-bonded network lying parallel to the (001) plane via strong O-H⋯O and O-H⋯N hydrogen bonds, leading to the formation of various hydrogen-bond ring motifs: dimeric R 2 2(8) and R 2 2(16) loops and a tetra-meric R 4 4(16) loop. The Hirshfeld surface analysis was also performed in order to better illustrate the nature and abundance of the inter-molecular contacts in the structure of 1.

A Molybdenum Trioxide Hybrid Decorated by 3-(1,2,4-Triazol-4-yl)adamantane-1-carboxylic Acid: A Promising Reaction-Induced Self-Separating (RISS) Catalyst.

3-(1,2,4-Triazol-4-yl)adamantane-1-carboxylic acid (tradcH), a heterobifunctional organic ligand in which carboxylic acid and 1,2,4-triazole groups are united through a rigid 1,3-adamantanediyl spacer, was employed for the synthesis of a MoVI oxide organic hybrid. The ligand crystallized from water as tradcH·H2O (1), possessing a two-dimensional hydrogen-bonding network, and from ethanol as a cyclic molecular solvate with the composition (tradcH)3·2EtOH (2). Treatment of tradcH with MoO3 under hydrothermal conditions afforded a new Mo trioxide hybrid, [MoO3(tradcH)]·H2O (3), which was structurally characterized. In 3, the molybdenum atoms form a polymeric zigzag chain of {μ2-O-MoO2}n which is supported by double triazole bridges, while the carboxylic acid termini are left uncoordinated. The coordination environment of the Mo centers appears as distorted cis-{MoN2O4} octahedra. The hybrid exhibits high thermal stability (up to 270 °C) and was employed for a relatively broad scope of catalytic oxidation reactions in the liquid phase. Its catalytic behavior may be compared to a reversible mutation, featuring the best sides of homogeneous and heterogeneous catalysis. The original solid material converts into soluble active species, and the latter revert to the original material upon completion of the catalytic reaction, precipitating and allowing straightforward catalyst separation/reuse (like a heterogeneous catalyst). This catalyst was explored for a chemical reaction scope covering sulfoxidation, oxidative alcohol dehydrogenation, aldehyde oxidation, and olefin epoxidation, using hydrogen peroxide as an eco-friendly oxidant that gives water as a coproduct.

New Microbe Killers: Self-Assembled Silver(I) Coordination Polymers Driven by a Cagelike Aminophosphine.

New Ag(I) coordination polymers, formulated as [Ag(µ-PTAH)(NO3)2]n (1) and [Ag(µ-PTA)(NO2)]n (2), were self-assembled as light- and air-stable microcrystalline solids and fully characterized by NMR and IR spectroscopy, electrospray ionization mass spectrometry (ESI-MS(±), elemental analysis, powder (PXRD) and single-crystal X-ray diffraction. Their crystal structures reveal resembling 1D metal-ligand chains that are driven by the 1,3,5-triaza-7-phospaadamantane (PTA) linkers and supported by terminal nitrate or nitrite ligands; these chains were classified within a 2C1 topological type. Additionally, the structure of 1 features a 1D→2D network extension through intermolecular hydrogen bonds, forming a two-dimensional hydrogen-bonded network with fes topology. Furthermore, both products 1 and 2 exhibit remarkable antimicrobial activity against different human pathogen bacteria (S. aureus, E. coli, and P. aeruginosa) and yeast (C. albicans), which is significantly superior to the activity of silver(I) nitrate as a reference topical antimicrobial.

Effect of high pressure on the typical 2D hydrogen-bonded crystal azodicarbonamide

We have performed in situ Raman scattering and synchrotron angle-dispersive X-ray diffraction (ADXRD) investigations to explore high-pressure behaviors of azodicarbonamide (C2N4O2H4, ADC) to 21.6 and 23.8 GPa, respectively. ADC exhibits the representative two-dimensional (2D) hydrogen-bonded networks, and is the most hugely used foaming agent in industry both under ambient and high pressures. Careful identification of external modes and indexation of Bragg diffraction peaks under different pressures demonstrate ADC crystal remains the P21/c symmetry in this study. The bulk modulus (B0) and its pressure derivative (B0’) are determined to be 13.2(7) GPa and 8.2(2) by fitting the isothermal third Vinet equation of state (EOS). The conformation change of ADC molecule has been observed at 12.7 GPa. And this is evidenced by the splitting of skeleton atoms vibrations and the discontinuous evolutions with respect to hydrogen bond donor (NH) vibrations. First principle calculation reveals the observed confirmation change arises from the discontinuous variation of the torsion angel between H2NC=O and CN=NC skeleton groups. Hirshfeld surface analysis indicates that the extensive hydrogen bonds within 2D networks dominate the intermolecular close contacts even under high pressures. The intermolecular interaction energy calculation also implies that the energy between neighboring molecules in the 2D layer dominates the networks stability, whereas the energy between neighboring molecules in the second nearest adjacent layer is the primary factor for crystal instability. The cooperativity of the molecular flexibility and directional hydrogen bonds is responsible for structural stability under high pressures.

Crystal structure, vibrational and optic properties of 2-N-methylamino-3-methylpyridine N-oxide – Its X-ray and spectroscopic studies as well as DFT quantum chemical calculations

The crystal and molecular structure and physicochemical properties of 2-N-methylamino-3-methylpyridine N-oxide (MA3MPO) have been studied. MA3MPO was synthesized from 2-amino-3-methylpyridine by several steps to form colorless crystals suitable for crystallographic analysis. The data reveal that MA3MPO crystallizes in the monoclinic space group P21/n. The studied compound contains a nearly flat triply substituted pyridine skeleton whose structure is stabilized by an intramolecular N–H⋅⋅⋅O hydrogen bond. The N-oxide molecules are connected together by weak C–H⋯O hydrogen bonds, an acceptor of which is the oxygen atom from the N-oxide group. This leads to creation of two-dimensional network of hydrogen bonds. Its IR, Raman, UV–Vis and luminescence spectra have been measured and analyzed on the basis of DFT and NBO quantum chemical calculations in which the B3LYP/6-311++G(d,p) approach was applied. The distribution of the electron levels in the studied compound has been analyzed in terms of the possibility of its participation in the ligand-to-lanthanide ion energy transfer.

Stepwise Synthesis, Hydrogen-Bonded Supramolecular Structure, and Magnetic Property of a Co–Mn Heterodinuclear Complex

A cobalt(III)–manganese(II) heterometallic dinuclear complex, [MnII{CoIII(µ-Himn)3}Cl2(CH3OH)], was prepared by a metalloligand approach. X-ray crystallographic analysis indicated that the metalloligand [CoIII(Himn)3] underwent mer/fac geometrical isomerization upon coordination to a Mn ion. Owing to the non-coordinating N–H bonds in the [CoIII(Himn)3] moiety, the heterodinuclear complex exhibited hydrogen bond interactions with the Cl− ligand of the neighboring complex to construct two-dimensional hydrogen-bond networks. The bond distances around the Mn center and the χMT value at 300 K indicate that the Mn center is in a divalent state. The temperature dependence of the χMT product and field dependence of the magnetization showed the isotropic nature of the MnII center.