Spodium bonds and metal–halogen···halogen–metal interactions in propagation of monomeric units to dimeric or polymeric architectures

A Nanosized Porous Supramolecular Lead(II)-N'-phenyl(pyridin-2-yl)methylene-N-phenylthiosemicarbazide Aggregate, Obtained Under Electrochemical Conditions

A novel nanosized porous supramolecular nonanuclear complex [Pb9(HL)12Cl2(ClO4)](ClO4)3·15H2O·a(solvent) (1·15H2O·a(solvent)) is reported that was synthesized by electrochemical oxidation of a Pb anode under the ambient conditions in a CH3CN:MeOH solution of N'-phenyl(pyridin-2-yl)methylene-N-phenylthiosemicarbazide (H2L), containing [N(CH3)4]ClO4 as a current carrier. The supramolecular aggregate of 1 is enforced by a myriad of Pb···S tetrel bonds (TtBs) established with the thiocarbonyl sulfur atoms of adjacent species, which have been also analyzed by DFT calculations via 2D maps of ELF, Laplacian and RDG properties. Moreover, Pb···Cl TtBs with the central Cl- anion, and Pb···O TtBs with the three oxygen atoms of the ClO4- anion, were revealed. Notably, the molecular structure of 1 differs significantly from that recently reported by us [Pb2(HL)2(CH3CN)(ClO4)2]·2H2O (2·2H2O), which was obtained using a conventional synthetic procedure by reacting Pb(ClO4)2 with H2L in the same CH3CN:MeOH solution, thus highlighting a crucial role of the electrochemical conditions. The optical characteristics of the complex were investigated using UV-vis spectroscopy and spectrofluorimetry in methanol. The complex was found to be emissive when excited at 304 nm, producing a broad emission band ranging from approximately 420 to 600 nm with multiple peaks. The CIE-1931 chromaticity coordinates, calculated as (0.33, 0.24), suggest that the emission lies in the white region of the chromaticity diagram. Further investigation is needed to fully characterize the origin of this emission.

Comparison of Intermolecular Halogen...Halogen Distances in Organic and Organometallic Crystals

Statistical analysis of halogen...halogen intermolecular distances was performed for three sets of homomolecular crystals under normal conditions: C-Hal1...Hal2-C distances in crystals consisting of: (i) organic compounds (set Org); (ii) organometallic compounds (set Orgmet); and (iii) distances M1-Hal1...Hal2-M2 (set MHal) (in all cases Hal1 = Hal2, and in MHal M1 = M2, M is any metal). When analyzing C-Hal...Hal-C distances, a new method for estimating the values of van der Waals radii is proposed, based on the use of two subsets of distances: (i) the shortest distances from each substance less than a threshold; and (ii) all C-Hal...Hal-C distances less than the same threshold. As initial approximations for these thresholds for different Hal, the Ragg values previously introduced in investigations with the participation of the author were used (Ragg values make it possible to perform a statistical assessment of the presence of halogen aggregates in crystals). The following values are recommended in this work to be used as universal values for crystals of organic and organometallic compounds: RF = 1.57, RCl = 1.90, RBr = 1.99, and RI = 2.15 Å. They are in excellent agreement with the results of some other works but significantly (by 0.10-0.17 Å) greater than the commonly used values. For the Orgmet set, slightly lower values for RI (2.11-2.09 Å) were obtained, but number of the C-I...I-C distances available for analysis was significantly smaller than in the other subgroups, which may be the reason for the discrepancy with value for the Org set (2.15 Å). Statistical analysis of the M-Hal...Hal-M distances was performed for the first time. A Hal-aggregation coefficient for M-Hal bonds is proposed, which allows one to estimate the propensity of M-Hal groups with certain M and Hal to participate in Hal-aggregates formed by M-Hal...Hal-M contacts. In particular, it was found that, for the Hg-Hal groups (Hal = Cl, Br, I), there is a high probability that the crystals have Hg-Hal...Hal-Hg distances with length ≤ Ragg.

The crystal structure of ((E)-2,4-dichloro-6-(((2-hydroxy-5-nitrophenyl)imino)methyl)phenolato-κ 3 N,O,O′)tris(pyridine-κN)manganese(II), C28H21Cl2MnN5O4

C28H21Cl2MnN5O4, triclinic, P 1 ‾ $P\overline{1}$ (no. 2), a = 8.9699(9) Å, b = 9.1185(9) Å, c = 17.6902(17) Å, α = 103.776(1)°, β = 92.407(1)°, γ = 99.761(1)°, V = 1379.8(2) Å3, Z = 2, R gt (F) = 0.0388, wR ref (F 2) = 0.0920, T = 296 K.

Noncovalent interactions in proteins and nucleic acids: beyond hydrogen bonding and π-stacking

Understanding the noncovalent interactions (NCIs) among the residues of proteins and nucleic acids, and between drugs and proteins/nucleic acids, etc., has extraordinary relevance in biomolecular structure and function. It helps in interpreting the dynamics of complex biological systems and enzymatic activity, which is esential for new drug design and efficient drug delivery. NCIs like hydrogen bonding (H-bonding) and π-stacking have been researchers' delight for a long time. Prominent among the recently discovered NCIs are halogen, chalcogen, pnictogen, tetrel, carbo-hydrogen, and spodium bonding, and n → π* interaction. These NCIs have caught the imaginations of various research groups in recent years while explaining several chemical and biological processes. At this stage, a holistic view of these new ideas and findings lying scattered can undoubtedly trigger our minds to explore more. The present review attempts to address NCIs beyond H-bonding and π-stacking, which are mainly n → σ*, n → π* and σ → σ* type interactions. Five of the seven NCIs mentioned earlier are linked to five non-inert end groups of the modern periodic table. Halogen (group-17) bonding is one of the oldest and most explored NCIs, which finds its relevance in biomolecules due to the phase correction and inhibitory properties of halogens. Chalcogen (group 16) bonding serves as a redox-active functional group of different active sites of enzymes and acts as a nucleophile in proteases and phosphates. Pnictogen (group 15), tetrel (group 14), triel (group 13) and spodium (group 12) bonding does exist in biomolecules. The n → π* interactions are linked to backbone carbonyl groups and protein side chains. Thus, they are crucial in determining the conformational stability of the secondary structures in proteins. In addition, a more recently discovered to and fro σ → σ* type interaction, namely carbo-hydrogen bonding, is also present in protein-ligand systems. This review summarizes these grand epiphanies routinely used to elucidate the structure and dynamics of biomolecules, their enzymatic activities, and their application in drug discovery. It also briefs about the future perspectives and challenges posed to the spectroscopists and theoreticians.

Structural Characterization of Multicomponent Crystals Formed from Diclofenac and Acridines

Multicomponent crystals containing diclofenac and acridine (1) and diclofenac and 6,9-diamino-2-ethoxyacridine (2) were synthesized and structurally characterized. The single-crystal XRD measurements showed that compound 1 crystallizes in the triclinic P-1 space group as a salt cocrystal with one acridinium cation, one diclofenac anion, and one diclofenac molecule in the asymmetric unit, whereas compound 2 crystallizes in the triclinic P-1 space group as an ethanol solvate monohydrate salt with one 6,9-diamino-2-ethoxyacridinium cation, one diclofenac anion, one ethanol molecule, and one water molecule in the asymmetric unit. In the crystals of the title compounds, diclofenac and acridines ions and solvent molecules interact via N–H⋯O, O–H⋯O, and C–H⋯O hydrogen bonds, as well as C–H⋯π and π–π interactions, and form heterotetramer bis[⋯cation⋯anion⋯] (1) or heterohexamer bis[⋯cation⋯ethanol⋯anion⋯] (2). Moreover, in the crystal of compound 1, acridine cations and diclofenac anions interact via N–H⋯O hydrogen bond, C–H⋯π and π–π interactions to produce blocks, while diclofenac molecules interact via C–Cl⋯π interactions to form columns. In the crystal of compound 2, the ethacridine cations interact via C–H⋯π and π–π interactions building blocks, while diclofenac anions interact via π–π interactions to form columns.