Ammonium N-(pyridin-2-ylmethyl)oxamate (AmPicOxam): A Novel Precursor of Calcium Oxalate Coating for Carbonate Stone Substrates

Ammonium N-(pyridin-2-ylmethyl)oxamate (AmPicOxam), synthesized from O-methyl-N-(pyridin-2-ylmethyl)oxamate, was spectroscopically and structurally characterized and assayed as a novel precursor for the protection and consolidation of carbonate stone substrates. An in-depth characterization of treated and untreated biomicritic limestone and white Carrara marble samples was carried out by means of SEM microscopy, X-ray powder diffraction, helium pycnometry, determination of water transport properties, and pull-off tests. The improved solubility (1.00 M, 16.5% w/w) of the title compound with respect to ammonium oxalate (0.4 M, 5% w/w) results in the formation of a thicker protective coating of calcium oxalate (CaOx) dihydrate (weddellite) on marble and biomicrite samples after the treatment with 5% and 12% w/w water solutions, producing a reduction in the stone porosity and increased cohesion. Theoretical calculations were carried out at the DFT level to investigate both the electronic structure of the N-(pyridin-2-ylmethyl)oxamate anion and the hydrolysis reaction leading from AmPicOxam to CaOx.

Unveiling the Impact of Aggregation on Optical Anisotropy of Triazaacephenanthrylene Single Crystals. A Combined Quantum Crystallography and Conceptual Density Functional Theory Approach

Triazaacephenanthrylene (TAAP) triclinic single crystals show substantial optical anisotropy of absorption and fluorescence. The maximum effect can be correlated with the direction perpendicular to the plane of chromophores connected in a head-to-tail manner via weak dispersive interactions. This phenomenon is uncommon as usually the existence of postulated π···π interactions between the molecules forming dimers or stacks cause quenching of fluorescence. Herein we present a comprehensive study of inter- and intramolecular interactions in the crystal of TAAP enriched with the investigation of aromaticity. Our results show that intramolecular interactions stabilize the overall conformation of the molecule whereas dispersive forces determine the aggregation between TAAP molecules. In fact, there is no conventional π···π interaction between the molecules in the dimer. Instead, we observed a close contact between the lone pair of the bridgehead N10B atom and π-deficient pyrazine ring from an adjacent molecule. Optical anisotropy in TAAP crystals was directly correlated with the alignment of the molecular transition dipole moments caused by specific molecular self-assembly.

The effects of deuteration-levels in solution and temperature on the segregation coefficient of the deuterium content in rapid-grown K(DxH1−x)2PO4 crystals via Raman spectroscopy

The correlation between the deuterium segregation coefficient and temperature, and the deuterium content in a solution was studied for the first time.

Intermolecular Interactions in Functional Crystalline Materials: From Data to Knowledge

Intermolecular interactions of organic, inorganic, and organometallic compounds are the key to many composition–structure and structure–property networks. In this review, some of these relations and the tools developed by the Cambridge Crystallographic Data Center (CCDC) to analyze them and design solid forms with desired properties are described. The potential of studies supported by the Cambridge Structural Database (CSD)-Materials tools for investigation of dynamic processes in crystals, for analysis of biologically active, high energy, optical, (electro)conductive, and other functional crystalline materials, and for the prediction of novel solid forms (polymorphs, co-crystals, solvates) are discussed. Besides, some unusual applications, the potential for further development and limitations of the CCDC software are reported.

A Million Crystal Structures: The Whole Is Greater than the Sum of Its Parts

The founding in 1965 of what is now called the Cambridge Structural Database (CSD) has reaped dividends in numerous and diverse areas of chemical research. Each of the million or so crystal structures in the database was solved for its own particular reason, but collected together, the structures can be reused to address a multitude of new problems. In this Review, which is focused mainly on the last 10 years, we chronicle the contribution of the CSD to research into molecular geometries, molecular interactions, and molecular assemblies and demonstrate its value in the design of biologically active molecules and the solid forms in which they are delivered. Its potential in other commercially relevant areas is described, including gas storage and delivery, thin films, and (opto)electronics. The CSD also aids the solution of new crystal structures. Because no scientific instrument is without shortcomings, the limitations of CSD research are assessed. We emphasize the importance of maintaining database quality: notwithstanding the arrival of big data and machine learning, it remains perilous to ignore the principle of garbage in, garbage out. Finally, we explain why the CSD must evolve with the world around it to ensure it remains fit for purpose in the years ahead.

Peculiarities of supramolecular organization of cyclic ketones with vinylacetylene fragments

1,5-Diaryl(heteroaryl)pentenynones show a tendency to crystallize in acentric space groups due to their inclination to form C-H...O hydrogen-bonded chains instead of dimers and thus exhibit nonlinear optical properties. A series of symmetrical α,α'-bis(3-arylprop-2-yn-1-ylidene)cycloalkanones and unsymmetrical α-(furan-2-ylmethylene)-α'-(3-arylprop-2-yn-1-ylidene)cyclohexanones closely related to pentenynones was synthesized, namely 2,5-bis(3-phenylprop-2-yn-1-ylidene)cyclopentanone, C₂₃H₁₆O, 2,5-bis[3-(4-bromophenyl)prop-2-yn-1-ylidene]cyclopentanone, C₂₃H₁₄Br₂O, 2,6-bis(3-phenylprop-2-yn-1-ylidene)cyclohexanone, C₂₄H₁₈O, 2,6-bis[3-(4-bromophenyl)prop-2-yn-1-ylidene]cyclohexanone, C₂₄H₁₆Br₂O, 4-tert-butyl-2,6-bis(3-phenylprop-2-yn-1-ylidene)cyclohexanone, C₂₈H₂₅O, 4-tert-butyl-2,6-bis[3-(4-methylphenyl)prop-2-yn-1-ylidene]cyclohexanone, C₃₀H₃₀O, 2-(furan-2-ylmethylene)-6-(3-phenylprop-2-yn-1-ylidene)cyclohexanone, C₂₀H₁₆O₂, and 6-(3-butylprop-2-yn-1-ylidene)-2-(furan-2-ylmethylene)cyclohexanone, C₁₀H₂₀O₂, and investigated by means of X-ray diffraction to understand peculiarities of their supramolecular organization. Four of the eight novel compounds crystallize in acentric space groups. Three of these four compounds contain substituents at the para position of the phenyl ring, which affect the charge density on the H(C_Ph) atoms and thus stabilize C_Ph-H...O interactions. The fourth compound realizes the C-H...O hydrogen bonding via H atoms of the furyl ring. The applicability and shortcomings of the Full Interaction Map tool to predict the likelihood of C-H...O and C-H...Br hydrogen-bonded motifs, and the effect of substituents on the phenyl ring on the supramolecular architecture are discussed.

Solvomorphs of tyraminium 5,5-diethylbarbiturate: a rare example of the barbiturate R33(12) hydrogen-bond motif and a crystal structure with Z' = 4

In the past two decades, the solvomorphism phenomenon in organic materials has attracted much attention, especially in the pharmaceutical and materials industries. Cocrystallization with solvent molecules can lead to modified physical and chemical properties of materials. We present here two new solvomorphs (pseudopolymorphs) of tyraminium 5,5-diethylbarbiturate [2-(4-hydroxyphenyl)ethanaminium 5,5-diethyl-2,4,6-trioxotetrahydro-2H-pyrimidin-1-ide, C₈H₁₂NO⁺·C₈H₁₁N₂O₃^-] with unusual structural features. Pseudopolymorph (I) follows the symmetry of the P2₁/n space group and has four tyraminium cations, four barbitalate anions and four molecules of chloroform in the asymmetric unit. Pseudopolymorph (II) crystallizes in the space group R-3c with one tyraminium cation, one barbitalate anion and a small amount of disordered solvent (ethanol and water) located in the cavities. Hirshfeld surface analysis and the Non-Covalent Interaction (NCI) index were used to examine and compare the crystal packing features and intermolecular interactions in (I) and (II). Both materials crystallize with large unit cells and contain nontypical barbitalate ions formed through deprotonation of the barbital N3 position. Pseudopolymorph (I) is an example of a crystal structure with a rarely observed value of Z' = 4. Analysis of the hydrogen-bond patterns in (II) showed an unusual arrangement of three barbitalate anions in R₃³(12) rings, which is the first example of such a hydrogen-bond motif in barbital structures. The mutual arrangement of the ions in the crystal structure of (II) leads to the formation of specific cavities along the c direction.