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Copper has been shown to be an important substrate for the growth of borophenes. Copper-boron binary clusters are ideal platforms to study the interactions between copper and boron, which may provide insight about the underlying growth mechanisms of borophene on copper substrates. Here we report a joint photoelectron spectroscopy and theoretical study on two copper-doped boron clusters, CuB7-and CuB8 Well resolved photoelectron spectra are obtained for the two clusters at different wavelengths and are used to understand the structures and bonding properties of the two CuBn- lusters. We find that CuB8 is a highly stable borozene complex, which possesses a half-sandwich structure with a Cu+ species interacting with the doubly aromatic Z8-B8²-borozene. The CuB7 - cluster is found to consist of a terminal copper atom bonded to a double-chain B7 motif, but it has a low-lying isomer composed of a half-sandwich structure with a Cu+ species interacting with an open-shell Z7-B7 2borozene. Both ionic and covalent interactions are found to be possible in the binary Cu-B clusters, resulting in different structures. [ABSTRACT FROM AUTHOR]

Hexamethylguanidinium bis(fluorosulfonyl)imide ([HMG][FSI]) has recently been shown to be a promising solid state organic ionic plastic crystal with potential application in advanced alkali metal batteries. This study provides a detailed exploration of the structural and dynamic behavior of [HMG][FSI] mixtures with the sodium salt NaFSI across the whole composition range from 0 to 100 mol%. All mixtures are solids at room temperature. A combination of differential scanning calorimetry (DSC), synchrotron X-ray diffraction (SXRD) and multinuclear solid state NMR spectroscopy is employed to identify a partial phase diagram. The 25 mol% NaFSI/75 mol% [HMG][FSI] composition presents as the eutectic composition with the eutectic transition temperature at 44 °C. Both DSC and SXRD strongly support the formation of a new compound near 50 mol% NaFSI. Interestingly, the 53 mol% NaFSI [HMG][FSI] composition was consistently found to display features of a pure compound whereas the 50 mol% materials always showed a second phase. Many of the compositions examined showed unusual metastable behaviour. Moreover, the ion dynamics as determined by NMR, indicate that the Na+ and FSI− anions are signifcantly more mobile than the HMG cation in the liquid state (including the metastable state) for these materials. [ABSTRACT FROM AUTHOR]

Developing chelators that strongly and selectively bind rare-earth elements (Sc, Y, La, and lanthanides) represents a longstanding fundamental challenge in inorganic chemistry. Solving these challenges is becoming more important because of increasing use of rare-earth elements in numerous technologies, ranging from paramagnets to luminescent materials. Within this context, we interrogated the complexation chemistry of the scandium(III) (Sc3+) trication with the hexadentate 1,4,7-triazacyclononane-1,4,7-triacetic acid (H3NOTA) chelator. This H3NOTA chelator is often regarded as an underperformer for complexing Sc3+. A common assumption is that metalation does not fully encapsulate Sc3+ within the NOTA3− macrocycle, leaving Sc3+ on the periphery of the chelate and susceptible to demetalation. Herein, we developed a synthetic approach that contradicted those assumptions. We confirmed that our procedure forced Sc3+ into the NOTA3− binding pocket by using single crystal X-ray diffraction to determine the Na[Sc(NOTA)(OOCCH3)] structure. Density functional theory (DFT) and 45Sc nuclear magnetic resonance (NMR) spectroscopy showed Sc3+ encapsulation was retained when the crystals were dissolved. Solution-phase and DFT studies revealed that [Sc(NOTA)(OOCCH3)]1− could accommodate an additional H2O capping ligand. Thermodynamic properties associated with the Sc-OOCCH3 and Sc-H2O capping ligand interactions demonstrated that these capping ligands occupied critical roles in stabilizing the [Sc(NOTA)] chelation complex. [ABSTRACT FROM AUTHOR]

The molecular tetravalent oxidation state for praseodymium is observed in solution via oxidation of the anionic trivalent precursor [K][Pr3+(NP(1,2-bis-tBu-diamidoethane)(NEt2))4] (1-Pr(NP*)) with AgI at −35 °C. The Pr4+ complex is characterized in solution via cyclic voltammetry, UV-vis-NIR electronic absorption spectroscopy, and EPR spectroscopy. Electrochemical analyses of [K][Ln3+(NP(1,2-bis-tBu-diamidoethane)(NEt2))4] (Ln = Nd and Dy) by cyclic voltammetry are reported and, in conjunction with theoretical modeling of electronic structure and oxidation potential, are indicative of principal ligand oxidations in contrast to the metal-centered oxidation observed for 1-Pr(NP*). The identification of a tetravalent praseodymium complex in in situ UV-vis and EPR experiments is further validated by theoretical modeling of the redox chemistry and the UV-vis spectrum. The latter study was performed by extended multistate pair-density functional theory (XMS-PDFT) and implicates a multiconfigurational ground state for the tetravalent praseodymium complex. [ABSTRACT FROM AUTHOR]

Using theoretical modeling to guide our approach, substituents were selected to improve the negative and positive potentials associated with a representative metal-based redox carrier, a phenyl spaced nickel bispicolinamide complex, [Ni(bpb)], 1. To broaden the cell potential, electron donating groups were selected and installed on the pyridyl moieties, [Ni(bpb-(NMe2)2)], 2, while electron withdrawing groups were incorporated on the phenyl linker, [Ni(bpb-R)] (R = –F, –CF3, and –NO2), 3–5. Our model predicts an increase of ∼300 mV and ∼500 mV for the first and second negative waves of Ni(bpb-NMe2), 2, and up to ∼330 mV and ∼210 mV increase to the first and second positive waves in 3–5. The modeled complexes were synthesized in good yields using a modification of the literature procedure. Due to limited solubility, the differential pulse voltammetry was measured on complexes 2–5 using a drop cast technique. Comparison of the observed and predicted potentials is discussed in acetonitrile (MeCN) and dimethylformamide (DMF) solvents. [ABSTRACT FROM AUTHOR]

Polymerized ionic liquids (PolyILs) are promising materials for applications in electrochemical devices spanning from fuel cells to capacitors and batteries. In principle, PolyILs have a competitive advantage over traditional electrolytes in being single ion conductors and thus enabling a transference number close to unity. Despite this perceived advantage, surprisingly low room temperature ionic conductivities measured in the lab raise an important fundamental question: how does the molecular structure mediate conductivity? In this work, wide-angle X-ray scattering (WAXS), vibrational sum frequency generation (vSFG), and density functional theory (DFT) calculations were used to study the bulk and interfacial structure of PolyILs, while broad band dielectric spectroscopy (BDS) was used to probe corresponding dynamics and conductive properties for a series of the PolyIL samples with tunable chemistries and structures. Our results reveal that the size of the mobile anions has a tremendous impact on chain packing in PolyILs that wasn’t addressed previously. Larger mobile ions tend to create a well-packed structure, while smaller ions frustrate chain packing. The magnitude of these changes and level of structural heterogeneity are shown to depend on the chemical functionality and flexibility of studied PolyILs. Furthermore, these experimental and computational results provide new insight into the correlation between conductivity and structure in PolyILs, suggesting that structural heterogeneity helps to reduce the activation energy for ionic conductivity in the glassy state. [ABSTRACT FROM AUTHOR]

Based on the idea of defect migration as the principal mechanism in the dielectric relaxation of ice Ih, the concept of low-temperature dynamic crossover was proposed. It is known that at high temperatures, the diffusion of Bjerrum and ionic defects is high and their movement may be considered to be independent. Simple switching between these two mechanisms leads to a dynamic crossover at ∼235 K. By introducing coupling between the Bjerrum and ionic defects, it is possible to describe the smooth bend in the relaxation time at low temperatures in ice Ih. However, because the mobility of Bjerrum orientation defects slows down at low temperatures, they may create blockages for proton hopping. The trapping of ionic defects by L-D defects for a long period of time leads to an increase in the relaxation time and causes a low-temperature crossover. This model was validated by experimental dielectric measurements using various temperature protocols. [ABSTRACT FROM AUTHOR]

Water is of fundamental importance for life. It plays a critical role in all biological systems. In phycocyanin, a pigment–protein complex, the hydration level influences its absorption spectrum. However, there is currently a gap in the understanding of how protein interfaces affect water's structure and properties. This work presents combined dielectric and calorimetric measurements of hydrated phycocyanin with different levels of hydration in a broad temperature interval. Based on the dielectric and calorimetric tests, it was shown that two types of water exist in the phycocyanin hydration shell. One is confined water localized inside the phycocyanin ring and the second is the water that is embedded in the protein structure and participates in the protein solvation. The water confined in the phycocyanin ring melts at the temperature 195 ± 3 K and plays a role in the solvation at higher temperatures. Moreover, the dynamics of all types of water was found to be effected by the presence of the ionic buffer. [ABSTRACT FROM AUTHOR]

A correlation between the long-range characteristics of the magnetic response of toroidal boron-based structures is given, involving the uncoordinated B16 cluster and the hypercoordinated [Co@B16]−/3− counterparts. It is found that the perfectly symmetrical doubly aromatic systems share common features, involving a continuous shielding region for the orientation-averaged response (isotropic), and a long-ranged shielding cone under a perpendicularly oriented applied field (Bextz). In contrast, the conflicting aromatic structure given by the slightly distorted species, exhibits an enhanced deshielding cone under Bextz, which dominates the isotropic character of the response. In addition, [Mn@B16]− and [Cu@B16]− clusters were evaluated, denoting the role of the coordinated metal atom in such property. This information is valuable to account for a global magnetic response driven by the bonding pattern acting in each respective compound, and for the possible characterization of intermolecular aggregates or extended structures via NMR experiments. [ABSTRACT FROM AUTHOR]

We discover unusual chemical bonding in a novel planar hyper-coordinate Ni2Ge free-standing 2D monolayer, and also in a nearly planar slightly buckled Ni2Si monolayer. This unusual bonding is revealed by Solid State Adaptive Natural Density Partitioning analysis. This analysis shows that a new type of 2c-2e Ni–Si σ and 3c-2e Ni–Ge–Ni σ bonds stabilize these 2D crystals. This is completely different from any previously known 2D crystals. Both of these free-standing monolayers are global minima in two-dimensional space. Although their exotic structure has unprecedented chemical bonding, they show extraordinary stability as single layers. The stabilities of these frameworks are confirmed by phonon dispersion calculations and ab initio molecular dynamics calculations. For Ni2Si, the framework was maintained during short 10 ps molecular dynamics annealing up to 1500 K, while Ni2Ge survived 10 ps runs up to 900 K. Both systems are predicted to be non-magnetic and metallic. As these new 2D crystals contain hypercoordinated Group 14 atoms, they are examples of a new class of 2D crystals with unconventional chemical bonding and potentially exciting new properties. Interestingly, we find that the stabilities of Ni2Si and Ni2Ge are much higher than that of silicene and germanene. Thus, this work provides a novel way to stabilize 2D sheets of Group 14 elements. [ABSTRACT FROM AUTHOR]

Group 13 elements are very rarely observed to catenate into linear chains and experimental observation of such species is challenging. Herein we report unique results obtained via combined photoelectron spectroscopy and ab initio studies of the Li2Al3H8− cluster that confirm the formation of an Al chain surrounded by hydrogen atoms in a very particular manner. Comprehensive searches for the most stable structure of the Li2Al3H8− cluster have shown that the global minimum isomer I possesses a geometric structure, which resembles the structure of propane, similar to the experimentally known Zintl-phase Cs10H[Ga3H8]3 compound featuring the propane-like [Ga3H8]3− polyanions. Theoretical simulations of the photoelectron spectrum have demonstrated the presence of only one isomer (isomer I) in the molecular beam. Chemical bonding analysis of the Li2Al3H8− cluster has revealed two classical Al–Al σ bonds constituting the propane-like kernel. [ABSTRACT FROM AUTHOR]

Over the last decade, discussions on a possible liquid–liquid transition (LLT) have strongly intensified. The LLT proposed by several authors focused mostly on explaining the anomalous properties of water in a deeply supercooled state. However, there have been no direct experimental observations yet of LLT in bulk water in the so-called ‘no man's land’, where water exists only in the crystalline states. Recently, a novel experimental strategy to detect LLT in water has been employed using water–glycerol (W–G) mixtures, because glycerol can generate a strong hindrance for water crystallization. As a result, the observed first-order phase transition at a concentration of glycerol around cg≈ 20 mol% was ascribed to the LLT. Here we show unambiguously that the first order phase transition in W–G mixtures is caused by the ice formation. We provide additional dielectric measurements, applying specific annealing temperature protocols in order to reinforce this conclusion. We also provide an explanation, why such a phase transition occurs only in the narrow glycerol concentration range. These results clearly demonstrate the danger of analysis of phase-separating liquids to gain better insights into water dynamics. These liquids have complex phase behavior that is affected by temperature, phase stability and segregation, viscosity and nucleation, and finally by crystallization, that might lead to significant misinterpretations. [ABSTRACT FROM AUTHOR]

Using quantum-chemical calculations and reduced dimensionality, we show that the “post-anti-van't Hoff-Le Bel” motif of germanium can be stabilized in a novel two-dimensional (2D) copper-germanium alloy film. This hypercoordinate sheet is the first stable planar hexacoordinate germanium material in 2D space. First principle calculations and molecular dynamics indicate that this Cu2Ge alloy film is a diamagnetic metal, and survives brief 10 ps annealing up to 1200 K. The electron delocalization and chemical bonding are unique and different from that of graphene, the all-boron α-sheet, and the BC3 honeycomb epitaxial sheet. Furthermore, we open a new route for the transformation of individual molecules to extended planar 2D sheets. This will provide new possibilities for extended planar hypercoordinate materials. We hope that these results will provide new opportunities to design post-anti-van't Hoff-Le Bel motifs by manipulation of dimensionality and quantum confinement. [ABSTRACT FROM AUTHOR]

The main mechanism of the dielectric relaxation process of ordinary hexagonal ice (ice Ih) and its temperature dependence remains unclear. The most interesting and as yet unexplained feature of ice is the presence of the dynamical crossover in relaxation time behavior around Tc = 230 ­ 3 K. Since there are no phase transitions in the ice at this temperature (first or second order), we cannot correlate the origin of this crossover with any structural change. Here we present a model according to which the temperature of the crossover is defined by the polarization mechanism. The dielectric relaxation driven by the diffusion of L-D orientational Bjerrum defects (at high temperature, T > Tc) is transformed into a dielectric relaxation dominated by the diffusion of intrinsic ionic H3O+/OH- defects (at low temperature, T < Tc). In the framework of the model, we propose an analytical equation for the complex dielectric permittivity that takes into account the contribution of both types of defects. [ABSTRACT FROM AUTHOR]

Copper has been shown to be an important substrate for the growth of borophenes. Copper-boron binary clusters are ideal platforms to study the interactions between copper and boron, which may provide insight about the underlying growth mechanisms of borophene on copper substrates. Here we report a joint photoelectron spectroscopy and theoretical study on two copper-doped boron clusters, CuB 7 - and CuB 8 - . Well resolved photoelectron spectra are obtained for the two clusters at different wavelengths and are used to understand the structures and bonding properties of the two CuB n - clusters. We find that CuB 8 - is a highly stable borozene complex, which possesses a half-sandwich structure with a Cu + species interacting with the doubly aromatic η 8 -B 8 2- borozene. The CuB 7 - cluster is found to consist of a terminal copper atom bonded to a double-chain B 7 motif, but it has a low-lying isomer composed of a half-sandwich structure with a Cu + species interacting with an open-shell η 7 -B 7 2- borozene. Both ionic and covalent interactions are found to be possible in the binary Cu-B clusters, resulting in different structures.

A series of Ce 3+ complexes with counter cations ranging from Li to Cs are presented. Cyclic voltammetry data indicate a significant dependence of the oxidation potential on the alkali metal identity. Analysis of the single-crystal X-ray diffraction data indicates that the degree of structural distortion of the secondary coordination sphere is linearly correlated with the measured oxidation potential. Solution electronic absorption spectroscopy confirms that the structural distortion is reflected in the solution structure. Computational studies further validate this analysis, deciphering the impact of alkali metal cations on the Ce atomic orbital contributions, differences in energies of Ce-dominant molecular orbitals, energy shift of the 4f-5d electronic transitions, and degree of structural distortions. In sum, the structural impact of the alkali metal cation is demonstrated to modulate the redox and electronic properties of the Ce 3+ complexes, and provides insight into the rational tuning of the Ce 3+ imidophosphorane complex oxidation potential through alkali metal identity., Competing Interests: The authors declare no conflict of interest., (This journal is © The Royal Society of Chemistry.)

Based on the idea of defect migration as the principal mechanism in the dielectric relaxation of ice I h , the concept of low-temperature dynamic crossover was proposed. It is known that at high temperatures, the diffusion of Bjerrum and ionic defects is high and their movement may be considered to be independent. Simple switching between these two mechanisms leads to a dynamic crossover at ∼235 K. By introducing coupling between the Bjerrum and ionic defects, it is possible to describe the smooth bend in the relaxation time at low temperatures in ice I h . However, because the mobility of Bjerrum orientation defects slows down at low temperatures, they may create blockages for proton hopping. The trapping of ionic defects by L-D defects for a long period of time leads to an increase in the relaxation time and causes a low-temperature crossover. This model was validated by experimental dielectric measurements using various temperature protocols.

A correlation between the long-range characteristics of the magnetic response of toroidal boron-based structures is given, involving the uncoordinated B 16 cluster and the hypercoordinated [Co@B 16 ] -/3- counterparts. It is found that the perfectly symmetrical doubly aromatic systems share common features, involving a continuous shielding region for the orientation-averaged response (isotropic), and a long-ranged shielding cone under a perpendicularly oriented applied field (B). In contrast, the conflicting aromatic structure given by the slightly distorted species, exhibits an enhanced deshielding cone under B, which dominates the isotropic character of the response. In addition, [Mn@B 16 ] - and [Cu@B 16 ] - clusters were evaluated, denoting the role of the coordinated metal atom in such property. This information is valuable to account for a global magnetic response driven by the bonding pattern acting in each respective compound, and for the possible characterization of intermolecular aggregates or extended structures via NMR experiments.

Although relating to the same system, the interpretations of the water spectra from Raman and Dielectric spectroscopy present independent pictures of the nature of water. We show that in the overlap region of the two methods it is possible to combine these views into a coherent concept of what drives the dynamic features of water. In this work, we develop the idea that the dielectric relaxation in water is driven by the migration of defects through the H-bond network, leading to a Debye-like peak in the lower frequencies. The deviation from the Debye law in the higher sub-THz frequencies is traced to a global fluctuation of the same H-bond network, clearly evident in the Raman Spectra. By incorporating these two views, a mathematical formalism is presented that can aptly explicate the dielectric spectra of liquid water.

Group 13 elements are very rarely observed to catenate into linear chains and experimental observation of such species is challenging. Herein we report unique results obtained via combined photoelectron spectroscopy and ab initio studies of the Li2Al3H8(-) cluster that confirm the formation of an Al chain surrounded by hydrogen atoms in a very particular manner. Comprehensive searches for the most stable structure of the Li2Al3H8(-) cluster have shown that the global minimum isomer I possesses a geometric structure, which resembles the structure of propane, similar to the experimentally known Zintl-phase Cs10H[Ga3H8]3 compound featuring the propane-like [Ga3H8](3-) polyanions. Theoretical simulations of the photoelectron spectrum have demonstrated the presence of only one isomer (isomer I) in the molecular beam. Chemical bonding analysis of the Li2Al3H8(-) cluster has revealed two classical Al-Al σ bonds constituting the propane-like kernel.

We discover unusual chemical bonding in a novel planar hyper-coordinate Ni2Ge free-standing 2D monolayer, and also in a nearly planar slightly buckled Ni2Si monolayer. This unusual bonding is revealed by Solid State Adaptive Natural Density Partitioning analysis. This analysis shows that a new type of 2c-2e Ni-Si σ and 3c-2e Ni-Ge-Ni σ bonds stabilize these 2D crystals. This is completely different from any previously known 2D crystals. Both of these free-standing monolayers are global minima in two-dimensional space. Although their exotic structure has unprecedented chemical bonding, they show extraordinary stability as single layers. The stabilities of these frameworks are confirmed by phonon dispersion calculations and ab initio molecular dynamics calculations. For Ni2Si, the framework was maintained during short 10 ps molecular dynamics annealing up to 1500 K, while Ni2Ge survived 10 ps runs up to 900 K. Both systems are predicted to be non-magnetic and metallic. As these new 2D crystals contain hypercoordinated Group 14 atoms, they are examples of a new class of 2D crystals with unconventional chemical bonding and potentially exciting new properties. Interestingly, we find that the stabilities of Ni2Si and Ni2Ge are much higher than that of silicene and germanene. Thus, this work provides a novel way to stabilize 2D sheets of Group 14 elements.

The main mechanism of the dielectric relaxation process of ordinary hexagonal ice (ice Ih) and its temperature dependence remains unclear. The most interesting and as yet unexplained feature of ice is the presence of the dynamical crossover in relaxation time behavior around Tc = 230 ± 3 K. Since there are no phase transitions in the ice at this temperature (first or second order), we cannot correlate the origin of this crossover with any structural change. Here we present a model according to which the temperature of the crossover is defined by the polarization mechanism. The dielectric relaxation driven by the diffusion of L-D orientational Bjerrum defects (at high temperature, T > Tc) is transformed into a dielectric relaxation dominated by the diffusion of intrinsic ionic H3O(+)/OH(-) defects (at low temperature, T < Tc). In the framework of the model, we propose an analytical equation for the complex dielectric permittivity that takes into account the contribution of both types of defects.

The chemical bonding analysis using the adaptive natural density partitioning method of the C4F fluorinated graphene sheet revealed a chemical bonding model explaining its particular stability. We proposed that the stability of the C4F fluorinated graphene is due to the so-called "benzation" of graphene. On the basis of our chemical bonding model we predicted that other high-symmetry structures of the C7F4, C3F2, C13F10, etc. stoichiometries, containing planar hexagons, which are separated from each other by 2, 3, 4, etc. C-F fragments could also possess additional stability. We also suggested that other functionalized graphene structures of the C4X and C7X4, C3X2, C13X10 stoichiometries, where X is a monovalent atom (H, F, Cl) or a monovalent group (CN, CCH etc.), could also have extra stability. We hope that the developed model, obtained for the functionalization of pristine graphene, will give an impetus for experimentalists to devise methods, which could serve as useful tools for producing this kind of materials with the tailored properties.