Charge density distributions in crystalline peroxosolvates of parabanic acid C3H2N2O3·0.5H2O2 and ammonium salt of 3,4,5-trinitropyrazole NH4+·C3N5O6-·0.5H2O2 derived from the high-resolution single-crystal X-ray experiments are reported with comparative periodic DFT calculations. Both multipole refinement and theoretical studies showed that the O-O bonds exhibit a (3, -1) critical point with electron density (ρb) of approximately 0.24 a.u. Experimental deformation density maps show not an accumulation but a depletion of charge density around O-O bond centers. The Laplacian values of electron density (∇2ρb) obtained from X-ray data are definitely positive and lie within 0.70-0.79 a.u. Theoretical values of ∇2ρb noticeably depend on the basis sets. They exhibit small, both positive and negative values for the modest basis sets and are around 0.3 a.u. for the pob-TZVP basis set. Thus, the O-O linkage can be considered as a specific ≪charge-shift≫ bond. The F-F bond in crystalline α-F2 exhibits similar features.

Intricate behavior of one-electron potentials from the Euler equation for electron density and corresponding gradient force fields in crystals was studied. Bosonic and fermionic quantum potentials were utilized in bonding analysis as descriptors of the localization of electrons and electron pairs. Channels of locally enhanced kinetic potential and the corresponding saddle Lagrange points were found between chemically bonded atoms linked by the bond paths. Superposition of electrostatic φ_es (r) and kinetic φ_k (r) potentials and electron density ρ(r) allowed partitioning any molecules and crystals into atomic ρ- and potential-based φ-basins; the φ_k-basins explicitly account for electron exchange effect, which is missed for φ_es-ones. Phenomena of interatomic charge transfer and related electron exchange were explained in terms of space gaps between ρ- and φ-zero-flux surfaces. The gap between φ_es- and ρ-basins represents the charge transfer, while the gap between φ_k- and ρ-basins is proposed to be a real-space manifestation of sharing the transferred electrons. The position of φ_k-boundary between φ_es- and ρ-ones within an electron occupier atom determines the extent of electron sharing. The stronger an H‧‧‧O hydrogen bond is, the deeper hydrogen atom’s φ_k-basin penetrates oxygen atom’s ρ-basin. For covalent bonds, a φ_k-boundary closely approaches a φ_es-one indicating almost complete sharing the transferred electrons, while for ionic bonds, the same region corresponds to electron pairing within the ρ-basin of an electron occupier atom.

Understanding of binding between antiretroviral agents and biomacromolecules is important for investigation of processes that proceed during therapy. The conformational stability, binding affinity and energies of interactions in the crystal, ligand-nucleobase pairs and ligand–receptor complexes were studied for 1-[2-(2-benzoylphenoxy)ethyl]-6-methyluracil (VMU-2012-05), a potential anti-HIV drug. The x-ray structure of the crystalline VMU-2012-05 was solved experimentally, and the analysis of intermolecular interactions has been performed by means of Quantum Theory “Atoms in Molecules” (QTAIM). Quantum chemical study of the isolated molecule revealed five stable conformations, their energies differ up to 14.3 kJ/mol, four of them can be described as folded and one as extended or linear. In the crystal, a folded conformation of VMU-2012-05 significantly differs from stable ones for an isolated molecule. Intermolecular interactions in the model complexes of VMU-2012-05 with nucleobases and the HIV-1 reverse transcriptase caused stabilization of the least favorable folded conformation for the molecule. QTAIM and NCI study revealed that the dimers between VMU-2012-05 and the nucleobases are assembled mainly via C-H...π and staking interactions, while in the crystal and the complex with the HIV-1 reverse transcriptase VMU-2012-05 readily forms strong hydrogen bonds. The number of potential acceptors of H-bonding in VMU-2012-05 molecule exceeds the number of donors (1 and 5) that limits the number of hydrogen bonds experimentally observed in the crystal. The number of H-bonds in the model binding pocket with extra donors and acceptors is higher, nevertheless, the energy which goes to N-H…O bonds in the crystal is nearly the same as in the binding pocket (-58.9 and -63.6 kJ/mol, respectively). However, value of the lattice energy is by 37.9 kJ/mol larger than the total energy of the intermolecular interactions with the HIV-1 receptor (-214.6 and -245.2 kJ/mol) due to additional hydrophobic interactions. These results indicate the role of weak van der Waals interactions in stabilization of VMU-2012-05 associates with nucleobases and HIV-1 reverse transcriptase.

Single-crystal samples of the 3R-CuCrO2 phase (R3m, a = 2.9613(2) Å, c = 17.098(2) Å) with a delafossite structure were grown by the flux method. Structural parameters were refined by X-ray structural analysis. The elemental composition of the grown crystals was confirmed by Auger electron spectroscopy. A threshold electric field switching effect from a high-resistance to a low-resistance state was discovered. The effect is characterized by a jump in electrical resistance (up to 5 orders of magnitude at E = 4.7 kV/cm, T = 120 K) and S-shaped current–voltage characteristics with a region of negative differential resistance. The temperature dependences of dielectric permittivity and dielectric loss tangent exhibit a Debye-type relaxation process with an activation energy of 0.51(3) eV. The observed features of dc conductivity, current–voltage characteristics, and dielectric properties interpreted on the basis of the existence of charge carriers in a small polaron state and the destruction of this state by the electric field.

For over a century, materials science has been focused on comparing magnetism and ferroelectricity, revealing similarities in order types, domains, hysteresis, and responses to external stimuli. The exceptional physical properties of magnets often originate from frustration, which can result from site disorder and lattice geometry. While disordered relaxor ferroelectrics exhibit ultra-high dielectric and piezoelectric properties and fingerprinted behavior similar to spin glasses, ferroelectric-like materials with clear geometrically frustrated states have not been previously identified. Here we introduce a new type of relaxor material, a geometrically frustrated relaxor, exemplified by a Bi2Ti2O7 single crystal with a compositionally ordered pyrochlore structure. Our findings demonstrate canonical relaxor behavior, including dielectric anomalies, dipole freezing, non-ergodicity and a lack of spontaneous phase transitions. Furthermore, we show the emergence of a unique dipole ice state upon cooling, arising from conflicting order parameters related to two mutually exclusive rigid unit modes of Bi4O' tetrahedral rotations. The coexistence of these rotations does not satisfy symmetry constraints, causing geometrical frustration and suppressing the long-range order. The results provide the structural mechanism of geometrical frustration manifestation in Bi-containing pyrochlores, opening up avenues for exploring exotic ground states and advanced functionalities in dielectric materials.

The effect of doping on the chemical and physical properties of semiconductors, alloys, ferroelectrics, glasses, and other substances has been a classic topic in materials science for centuries. Strontium titanate, SrTiO3, is an archetypal perovskite of interest for both fundamental science as quantum paraelectric and numerous outstanding physical properties and applications, including dielectrics, tunable microwave and photovoltaic devices, superconductors, thermoelectrics, potential multiferroics. Its chemical doping with transition metals leads to new functionalities, but intrinsic mechanisms of structural responses, activated by impurities, have not been systematically investigated. Herein, we present the results of a comparative study of the crystal structure, vibrational spectra, and dielectric properties of SrTiO3:M (M = Mn, Ni, and Fe, 2 at%) single crystals. It is shown that impurities constitute a different tendency to off-centering and the formation of dipoles: Mn and Fe atoms are shifted from the center of the oxygen octahedron, while Ni atoms remain on-centered. As a result, small chemical doping has a dramatic effect on the dielectric response through various structural mechanisms, including the pseudo Jahn-Teller effect, the first-order Jahn-Teller effect, and defect-induced distortion. These findings open up fundamentally new possibilities for the practical solution of a difficult problem: controlling the dielectric responses of quantum paraelectrics by choosing the type of chemical additive.

The nature and strength of interactions for an anti-HIV drug, Lamivudine, were studied in a pure crystal form of the drug and the ligand–receptor complexes. High-resolution single-crystal X-ray diffraction studies of the tetragonal polymorph allowed the drug’s experimental charge density distribution in the solid state to be obtained. The QM/MM calculations were performed for a simplified model of the Lamivudine complex with deoxycytidine kinase (two complexes with different binding modes) to reconstruct the theoretical charge density distribution. The peculiarities of intramolecular interactions were compared with previously reported data for an isolated molecule. Intermolecular interactions were revealed within the quantum theory of ‘Atoms in Molecules’, and their contributions to the total crystal energy or ligand–receptor binding energy were evaluated. It was demonstrated that the crystal field effect weakened the intramolecular interactions. Overall, the energies of intermolecular interactions in ligand–receptor complexes (320.1–394.8 kJ/mol) were higher than the energies of interactions in the crystal (276.9 kJ/mol) due to the larger number of hydrophilic interactions. In contrast, the sum of the energies of hydrophobic interactions was found to be unchanged. It was demonstrated by means of the Voronoi tessellation that molecular volume remained constant for different molecular conformations (250(13) Å3) and increased up to 399 Å3 and 521(30) Å3 for the Lamivudine phosphate and triphosphate.

Single crystal X-ray diffraction (XRD), thermogravimetric, and dielectric studies are performed for single and polycrystalline samples of [(1–x)PbO + xWO3], 0≤ x ≤0.20, synthesized by solid phase reactions and crystallization of melts. The formation of previously unknown solid solutions based on the tetragonal form of lead oxide (α-PbO) – Pb1–2xWxO1+x, x ≈ 0.05 is observed. Single crystals of solid solutions are analyzed by XRD at 100 K and 293 K. It is found that their crystal structure isotypical to α-PbO is characterized by the orthorhombic space group Cmma with unit cell parameters (293 K) a = 5.510 Å, b = 5.570 Å, c = 5.301 Å. The main structural characteristics of solid solutions are determined. A structural model of the formation of solid solutions is established, according to which partial W substitution for Pb in α-PbO is accompanied by the inclusion of additional oxygen atoms to the location of lone pairs of substituted Pb2+ and the formation of vacancies in this cation sublattice. Temperature dependences of the permittivity and losses of solid solution crystals studied in the temperature range T = 80-570 K and at frequencies f = 1-1000 kHz do not have features characteristic of phase transitions.

Путем медленного охлаждения расплавов получены монокристаллы (Pb0.86Sr0.14)5Ge3O11. Изучено влияние облучения высокоэнергетическими электронами флюенсами до 6.2×1018э/cм2 на структурные и диэлектрические свойства этих кристаллов. Изучена зависимость параметров кристаллической структуры от величины флюенсов, установлен структурный механизм избирательного замещения Pb на Sr. Найдено, что позиции свинца с неподеленной парой электронов остаются свободными от замещения катионами стронция. Вплоть до флюэнса 6.2×1018э/cм2 структура (Pb0.86Sr0.14)5Ge3O11 сохраняет совершенство. Показано, что облучение данными флюенсами сохраняет параэлектрическую структуру при 293К (пр. гр. P) и приводит лишь к незначительным изменениям атомных смещений. Характер температурных зависимостей диэлектрических проницаемости и потерь (в интервалах 5-300 K и 1-1000 кГц) указывает, что облучение сопровождается как смещением ТС от 158 K до 145 K, так и усилением размытия сегнетоэлектрического фазового перехода.

This paper presents a binding approach based on the electrostatic and kinetic force density fields and proposed to elucidate interatomic interactions, structures, and chemical reactions. Among other elements, it consists in the understanding of (i) the arrangement of pseudoatomic zero-flux surfaces (ZFSs), (ii) the mutual compression of force-field pseudoatoms of the same type, (iii) the penetration of a bonded atom into neighboring force field pseudoatoms, (iv) the distortion of the force fields, and (v) the occurrence of a binding path connecting two force-field attractors as the inherent consequences of the emergence and existence of any many-electron multinuclear system. Herein, the interatomic charge transfer and the reciprocal quantum-chemical response accompanying the covalent and noncovalent bond formation were studied using the abovementioned penetration, exemplified by Appel's salt. Such consideration gave rise to the concept of force-induced "push-pull" assembling of interacting (pseudo)atoms. In this regard, various halogen, chalcogen, and tetrel noncovalent interactions, as well as polar covalent bonds, were examined. Furthermore, the notion of the force-based binding structure was proposed instead of the bonding one, which defines the mutual connectivity of force-field pseudoatoms of the same type via binding paths. The thus-defined chemical structure proved to be more sensitive to variations in the configuration space of nuclear coordinates. It was found that the three-center chalcogen bonding Cl-center dot center dot center dot S-S and tetrel bonding Cl-center dot center dot center dot C center dot center dot center dot Cl- in the crystal studied resemble the initial and transition states of bimolecular nucleophilic substitution reactions, respectively. Their central atoms act as electron contributors with a different degree of the transferred electron density sharing. Being extracted from the crystal structure, the corresponding ion pairs undergo chemical rearrangement: Forming the covalent bonds Cl-S and Cl-C leads to the collapse of the pseudoatomic ZFSs and the alignment of the bond and binding paths in the internuclear regions.

Single crystals of (Pb0.86Sr0.14)5Ge3O11 are prepared by a slow melt cooling. The effect of high-energy electron irradiation with fluences up to 6.2·1018 e/cm2 on the structural and dielectric properties of these crystals is studied; the dependence of crystal structure parameters on the fluences is considered; the structural mechanism of selective substitution of Pb by Sr is established. It is determined that the sites occupied by lead with a lone pair are not substituted by strontium cations. Up to the fluences of 6.2·1018 e/cm2, the (Pb0.86Sr0.14)5Ge3O11 structure remains perfect. It is shown that the irradiation with these fluences preserves the paraelectric structure at 293 K ( $$P\bar{6}$$ space group) and causes only minor atomic displacements. The temperature dependences of the dielectric permittivity and the dielectric loss (in the ranges of 5-300 K and 1-1000 kHz) show that the irradiation shifts TC from 158 K to 145 K and increases the diffusion of the ferroelectric phase transition.

Stoichiometric single crystals of Pb 5 (Ge 1– х Si x ) 3 O 11 solid solutions (0 ≤ x ≤ 0.55) are obtained by slow cooling of 5PbO·3(1– y )GeO 2 ·3 y SiO 2 melts. The chemical analysis confirms their cation and anion stoichiometry. The effect of their high-energy (10 MeV) electron irradiation with fluences from 0.1·10 18 e/cm 2 to 4.39·10 18 e/cm 2 on the structural, ferroelectric, and nonlinear optical characteristics of the crystals is studied for the first time. The dependence of crystals on concentrations and fluences is detected. According to the date of dielectric spectroscopy and second harmonic generation of laser radiation, the doping with Si causes a systematic shift of T c to low temperatures, a decrease in the peak value of the dielectric permittivity, and a noticeable phase transition smearing with transforming to the zelaxor ferrollectric state of x = 0.35. According to the structural studies of initial and irradiared, Pb 5 (Ge 1– x Si x ) 3 O 11 crystals, they retain the structural perfectness without any signs of amorphization. Structural distortions of Pb 5 (Ge 1– x Si x ) 3 O 11 do not significantly depend on the fluence.

влияние облучения высокоэнергетическими электронами на структурные, диэлектрические и нелинейно-оптические свойства монокристаллов твердых растворов pb5(ge1-хsix)3o11 (0≤x≤0.55) (готовится к публикации)

На синтезированных методом твердофазных реакций и кристаллизацией расплавов поли- и монокристаллических образцах [(1-x)PbO + xWO3], 0≤x≤0.20 выполнены рентгеноструктурные, термогравиметрические и диэлектрические исследования. Зафиксировано образование неизвестных ранее твердых растворов на основе тетрагональной формы оксида свинца (a-PbO) - Pb1-2xWxO1+x, x≈0.05. Выполнен рентгеноструктурный анализ монокристаллов твердых растворов при 100К и 293К. Установлено, что их кристаллическая структура изотипна a-PbO, она характеризуется ромбической пространственной группой Cmma с размерами элементарной ячейки, равными при 293K a=5.510 Å, b=5.570 Å, c=5.301 Å. Определены основные структурные характеристики твердых растворов. Установлена структурная модель образования твердых растворов, согласно которой частичное замещение Pb на W в a-PbO сопровождается внедрением дополнительных атомов кислорода в места расположения неподеленных пар электронов замещаемых Pb2+ и образованием вакансий в этой катионной подрешетке. На изученных в области температур T=80–570К на частотах f=1–1000 кГц температурных зависимостях диэлектрических проницаемости и потерь кристаллов твердых растворов не наблюдается особенностей, характерных для фазовых переходов.

На выращенных методом раствор-расплавной кристаллизации монокристаллах фазы Pb6Sb2O11 выполнены рентгеноструктурные и диэлектрические исследования. Впервые определена ее кристаллическая структура, выяснена роль неподеленной пары электронов свинца. На изученных в области 80-940 К и диапазоне частот 0.1-200 кГц температурно-частотных зависимостях диэлектрической проницаемости e и тангенса угла диэлектрических потерь tgd не наблюдается особенностей, характерных для фазовых переходов.

X-ray diffraction and dielectric studies of the Pb 6 Sb 2 O 11 phase are conducted using flux-grown single crystals. The crystal structure of the phase is determined for the first time, the role of the lead lone pair is clarified. In the studied temperature (80-940 K) and frequency (0.1-200 kHz) ranges, the temperature-frequency dependences of the dielectric constant ε and the dielectric loss tangent tanδ show no features characteristic of phase transitions.

Single crystals of the Pb5WO8 phase were grown in the PbO–WO3 system by crystallization of (1 – x)PbO·xWO3 (x = 0.15–0.20) mixed melts. Thermogravimetric, X-ray diffraction, and dielectric studies of the single crystals were carried out. The phase melts at 712°С with decomposition to PbO and a liquid. The Pb5WO8 crystal structure is monoclinic (space group P21/n, 293 K) with the unit cell parameters a = 7.4430(1) Å, b = 12.1156(2) Å, c = 10.6284(2) Å, β = 90.658(1)°. The Pb5WO8 structure is retained at 100 K; the minor alterations in unit cell parameters are associated only with thermal expansion. The Pb5WO8 structure has a pronounced layered character; it appears as an alternation of layers formed of WO6 octahedra and strongly distorted PbO4 and PbO5 polyhedra in the direction [010]. A detailed crystal-chemical analysis of the structure was carried out. An important role of the Pb lone pair in the formation of characteristic voids in the structure was noted. The temperature-dependent dielectric permittivity and dielectric loss tangent feature relaxation peaks associated with lead and oxygen vacancies in the structure.

An entry from the Inorganic Crystal Structure Database, the world’s repository for inorganic crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the joint CCDC and FIZ Karlsruhe Access Structures service and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

Herein, we experimentally obtained and studied the inner-crystal scalar potential fields and the associated vector force fields of static and kinetic nature in picolinic acid N-oxide (PANO) and methimazole. The "through-bond" and "through -space" electronic effects were defined and distinguished via the vector fields and concurred with the penetration of the electron contributor's electrostatic and kinetic force field pseudoatoms (phi es-and phi k-basins) into the occupier's chemical atom (rho- basin). A special focus was given to the dipolar N+-O- bond as well as to the thioamide N-C=S and carboxylic O=C-OH fragments. An unusual way of interatomic charge transfer was revealed between two nonbonded hydrogen atoms [COO-]H center dot center dot center dot H[-C] in the PANO crystal. The experimental electric and kinetic force fields in the molecular crystals were compared to the theoretical ones for the free molecules and hydrogen-bonded associates, which helped figure out the natural consequences of the crystal packing effect. As expected, the appearance of neighboring attractors in a dense crystal packing requires zero-flux surfaces (ZFSs) emerging in the vector fields and the compression of the outer force field pseudoatoms of a molecule. We proposed to consider a ZFS in the kinetic force field to be a turning surface for electrons in the sense that an electron passed through the boundary is immediately affected by the redirected force attributed to another attractor. The strengthening and noticeable increase observed in the covalency of the intramolecular hydrogen bond O-H center dot center dot center dot O in the PANO crystal is a direct consequence of such compression of the hydrogen atom and pseudoatoms by the inner-crystal environment. The Pauli and fermionic scalar and vector fields were applied to locate electron lone pairs and describe their involvement in noncovalent interactions within the donor-acceptor mechanism.

Stoichiometric (Pb 0.89 Ba 0.11 ) 5 Ge 3 O 11 single crystals have been grown under conditions of slow melt cooling. The influence of irradiation by high-energy (10 MeV) electrons on the structural and dielectric characteristics of these crystals has been studied for the first time. The paraelectric structure of the crystals (sp. gr. P 6̅ ) is found to retain at 293 K after the irradiation. The influence of a lone electron pair on the substitution of Pb for Ba is found. Despite the irradiation with a fluence up to 6.2 × 10 18 cm –2 , (Pb 0.89 Ba 0.11 ) 5 Ge 3 O 11 single crystals retain their structural quality. Temperature dependences of the permittivity and dielectric loss (in the temperature range of 5–300 K and the frequency range of 1–1000 kHz) indicate that the irradiation shifts the Curie point from 123 to 95 K and increases broadening of the ferroelectric phase transition.