The electronic diffuse reflectance spectra of a series of seven neodymium (III) tetrakis complexes with carbacylamidophosphate (CAPh) ligands were investigated to evaluate the influence of ligand substituents, nature of counter cation, coordination geometry, and Nd—O bond distances on the degree of metal–ligand bond covalency. The spectra exhibit intense ligand-centered absorption in the UV region and characteristic narrow intraconfigurational 4f–4f absorption bands of the NdIII ion in the visible and near-infrared regions. The positions of the selected f–f transition bands were used to calculate the averaged nephelauxetic parameters using both the free gaseous NdIII ion and the NdIII aqua ion as reference systems 1 and 2, respectively. In addition, Sinha’s covalency parameter (δ), the bonding parameter (b1/2), and the angular overlap parameter (η) were determined relative to the NdIII aqua ion. The averaged nephelauxetic parameters are smaller than unity for all investigated compounds and lie in the ranges of 0.97529-0.97985 for β1 and 0.99167-0.99591 for β2, demonstrating a measurable nephelauxetic effect throughout the series. The calculated Sinha’s covalency parameters, δ = 0.4109-0.8397%, indicate a weak covalent contribution to the predominantly ionic Nd—O bonds. Comparison of complexes containing identical CAPh ligands but different outer-sphere cations revealed an increase in the nephelauxetic parameters upon replacement of tetraethylammonium by alkali-metal cations. Complexes containing the same tetraethylammonium counter cation but different CAPh ligands exhibit variations in the spectroscopic covalency parameters, indicating an influence of the substituents attached to the phosphoryl and carbonyl groups. No simple correlation was found between the average Nd—O bond distances and the magnitude of the nephelauxetic effect: complexes with shorter Nd—O distances do not necessarily exhibit a greater metal-ligand bond covalency, as evaluated spectroscopically.
This review systematizes the least understood aspects of the structure of inorganic compounds at three levels: partial models, real structure, and orders that extend beyond atomic coordinates. It is shown that structural inorganic chemistry does not operate with a single unifying theory but with a mosaic of partial models – the ionic model with Pauling's rules, the valence-shell electron-pair repulsion (VSEPR) model, the Wade-Mingos rules, the Zintl-Klemm concept, and band theory – each of which has a poorly delineated domain of applicability. A direct statistical test of classical crystal-chemical rules against large experimental datasets has revealed unexpectedly low predictive power, including for Pauling's rules and the Goldschmidt tolerance factor. The review further addresses crystal structure prediction as an NP-hard optimization problem; the least-studied structural states and phenomena, including the amorphous state, correlated disorder, nonstoichiometry (Berthollide phases), mixed valence, the stereochemical activity of lone pairs, quasicrystals, high-pressure chemistry, 5f-electron systems, and the superionic state; the genesis of structure through classical and non-classical nucleation theory; the real, defective architecture of grain boundaries and complexions, dislocations in ionic crystals, polar surfaces, and the solid-water interface; the discrepancy between average crystallographic structure and local dynamic structure in BaTiO3, relaxor ferroelectrics, and halide perovskites; configurationally complex and high-entropy phases; and the methodological reliability of structural databases, including documented cases of misassigned space groups and fabricated structures. A separate section systematizes orders that are not reducible to atomic positions: charge, spin, and orbital ordering (the Mott-Peierls problem in VO2, charge density waves, the cuprate pseudogap), magnetic crystallography and the recently established class of altermagnets (including the ongoing revision of its reference material), the topological dimension of structure and the role of spin-orbit coupling, hydrogen as a systematic blind spot of X-ray diffraction rather than of diffraction as such (including the reproducibility crisis surrounding claims of room-temperature superconductivity), chemical bonds that resist classification (electrides, quintuple bonds, metallophilic and sigma-hole interactions), and non-equilibrium hidden phases. Two constructive counterexamples are discussed at length: the modern (Berry-phase) theory of polarization and quantum crystallography, both of which show that the atomic-coordinate model can be correctly extended rather than merely declared incomplete. It is argued that quantum mechanics constitutes a unified theory of structure only in Dirac's foundational sense, while, operationally, structural chemistry remains irreducibly pluralistic and multi-object, in the sense articulated by Anderson's emergentism. A productive research program is therefore identified not as the pursuit of a single all-encompassing theory, but as the systematic mapping of the domains of applicability of existing models, the construction of transition rules between them, and the well-defined extension of the structural model itself. The practical stakes of this program are illustrated through composite ion-exchangers and carbon-nanomaterial-functionalized membranes, in which the poorly characterized structure of the disordered hydrous-oxide layer directly governs sorption selectivity and ion transport.
The composites based on ((Mg2+/Zn2+), Na+, SiO44-, BO33-)-substituted hydroxyapatites with SiO2 were synthesized from aqueous solutions and subsequently annealed at temperatures of 600 and 800 °C. The resulting materials were characterized using X-ray powder diffraction and FTIR spectroscopy, and their effect on the pH of a model solution (pH = 7.40 at 37 °C) was evaluated depend on composition. X-ray powder diffraction confirmed the formation of apatite-type phases, while FTIR spectroscopy confirmed the partial substitution of phosphate and hydroxide anions by BO33- and BO2- groups, respectively as well as the presence of SiO2. It was found that the crystal size of the apatite-type phase does not depend on the divalent metal and ranges from 16 to 17 nm, while the presence of silica enhances the thermal stability of the composites and their resistance to aggregation during annealing at 800 °C. It has been shown that the nature of the divalent metal significantly influences the dissolution behavior of the composites in a model solution. Zinc-containing composites are characterized by higher dissolution activity during the first two hours, which persists for the following 24 hours. In contrast, the magnesium-containing composite exhibits moderate activity during the first two hours of testing, but its activity increases significantly over the next 48 hours. An increase in the silica content to 50 wt%, despite a decrease in the phosphate component, is accompanied by an increase in the composite’s activity, indicating the important role of the silicate component in the processes of dissolution and the material’s interaction with the simulated physiological medium. The proposed approach makes it possible to produce composite materials with predetermined properties that can subsequently be used in bone tissue engineering.
A method for the synthesis of functionalized tetraalkylammonium surfactants was proposed and their micellar effects were studied during the decomposition of 4-nitrophenyldiethylphosphonate, a product structurally similar to synthetic and natural ecotoxicants and combat toxic agents. The reactivity of co-micellar systems based on functionalized imidazolium and tetraalkylammonium surfactants in the process of 4-nitrophenyldiethylphosphonate cleavage was studied. When the imidazolium fragment in the detergent structure is replaced by a tetraalkylammonium one, the efficiency of substrate solubilization decreases. In the case of dimeric surfactants, a rather significant decrease in the nucleophilicity of the oximate fragment (by ~2 times) is also observed, which additionally reduces the rate of cleavage of the organophosphorus substrate. Therefore, the nature of the cationic center of the head group can affect the magnitude of the observed micellar effects of functionalized surfactants. The effect of detergents on the rate of ester cleavage was compared with the micellar effects of their structural analogues – imidazolium surfactants, which allows us to analyze the influence of the nature of the cationic center on their reactivity. In the nucleophilic destruction of esters of phosphorus and sulfur acids in micellar systems, the greatest observed effects were achieved when using surfactants functionalized with α-nucleophile fragments as cleavage agents. The undoubted advantage of such detergents over other types of micellar systems is the absence of the need for reagent binding. In this case, binding will always be maximum, since the reactive fragment of the molecule is covalently bound to the surfactant. One of the key factors determining the reactivity of the system should be considered the nature of the head group, since it largely determines the structure, surface charge, partial molar volume of the micelle, saturation of the surface layer of the micelle with water molecules, etc.
Children exposed to war experience severe neurodevelopmental disruption from the combined effects of chronic stress, malnutrition, environmental toxins, and psychological trauma during critical windows of brain development. These overlapping insults impair synaptogenesis, myelination, and the maturation of stress‑regulation circuits, creating long‑term risks for cognitive deficits, emotional dysregulation, and reduced educational and social outcomes. Nutritional biochemistry, neurochemistry, and molecular medicine offer evidence‑based strategies to protect the developing brain under these extreme conditions and to mitigate the biological consequences of trauma. Key micronutrients—such as iron, iodine, zinc, and magnesium—along with long‑chain omega‑3 fatty acids and enzymatic cofactors essential for neurotransmitter synthesis, can stabilize the hypothalamic–pituitary–adrenal axis, reduce neuroinflammation, support mitochondrial function, and preserve synaptic plasticity. Advances in formulation chemistry now enable stable, low‑cost, field‑deployable pediatric supplements that remain viable despite disrupted supply chains, limited refrigeration, and damaged infrastructure. In parallel, portable chemical sensors and rapid analytical platforms can detect heavy metals, explosive residues, and other neurotoxic contaminants in water and soil, preventing secondary exposure that further threatens vulnerable developing nervous systems. By elucidating the molecular pathways of trauma—including cortisol dysregulation, oxidative stress, excitotoxicity, and impaired neuroplasticity—chemistry provides rational targets for timely intervention and guides the design of protective strategies suited for conflict zones. While chemistry cannot end war, it can meaningfully preserve cognitive potential, psychological resilience, and the possibility of healthy development in the youngest victims of armed conflict.
