Two-dimensional monolayer salt nanostructures can spontaneously aggregate rather than dissolve in dilute aqueous solutions

It is well known that NaCl salt crystals can easily dissolve in dilute aqueous solutions at room temperature. Herein, we reported the first computational evidence of a novel salt nucleation behavior at room temperature, i.e., the spontaneous formation of two-dimensional (2D) alkali chloride crystalline/non-crystalline nanostructures in dilute aqueous solution under nanoscale confinement. Microsecond-scale classical molecular dynamics (MD) simulations showed that NaCl or LiCl, initially fully dissolved in confined water, can spontaneously nucleate into 2D monolayer nanostructures with either ordered or disordered morphologies. Notably, the NaCl nanostructures exhibited a 2D crystalline square-unit pattern, whereas the LiCl nanostructures adopted non-crystalline 2D hexagonal ring and/or zigzag chain patterns. These structural patterns appeared to be quite generic, regardless of the water and ion models used in the MD simulations. The generic patterns formed by 2D monolayer NaCl and LiCl nanostructures were also confirmed by ab initio MD simulations. The formation of 2D salt structures in dilute aqueous solution at room temperature is counterintuitive. Free energy calculations indicated that the unexpected spontaneous salt nucleation behavior can be attributed to the nanoscale confinement and strongly compressed hydration shells of ions.

Zhang–Zhang Polynomials of Multiple Zigzag Chains Revisited: A Connection with the John–Sachs Theorem

Multiple zigzag chains Zm,n of length n and width m constitute an important class of regular graphene flakes of rectangular shape. The physical and chemical properties of these basic pericondensed benzenoids can be related to their various topological invariants, conveniently encoded as the coefficients of a combinatorial polynomial, usually referred to as the ZZ polynomial of multiple zigzag chains Zm,n. The current study reports a novel method for determination of these ZZ polynomials based on a hypothesized extension to John–Sachs theorem, used previously to enumerate Kekulé structures of various benzenoid hydrocarbons. We show that the ZZ polynomial of the Zm,n multiple zigzag chain can be conveniently expressed as a determinant of a Toeplitz (or almost Toeplitz) matrix of size m2×m2 consisting of simple hypergeometric polynomials. The presented analysis can be extended to generalized multiple zigzag chains Zkm,n, i.e., derivatives of Zm,n with a single attached polyacene chain of length k. All presented formulas are accompanied by formal proofs. The developed theoretical machinery is applied for predicting aromaticity distribution patterns in large and infinite multiple zigzag chains Zm,n and for computing the distribution of spin densities in biradical states of finite multiple zigzag chains Zm,n.

A 2-D Zn(II) coordination polymer based on 4,5-imidazoledicarboxylate and bis(benzimidazole) ligands: synthesis, crystal structure and fluorescence properties

In this work, a new type of zinc(II) coordination polymer {[Zn(HIDC)(BBM)0.5]·H2O} n (Zn-CP) was synthesized using 4,5-imidazoledicarboxylic acid (H3IDC) and 2,2-(1,4-butanediyl)bis-1,3-benzimidazole (BBM) under hydrothermal conditions. Its structure has been characterized by infrared spectroscopy, elemental analysis and single crystal X-ray diffraction analysis. The Zn(II) ion is linked by the HIDC2− ligand to form a zigzag chain by chelating and bridging, and then linked by BBM to form a layered network structure. Adjacent layers are further connected by hydrogen bond interaction to form a 3-D supramolecular framework. The solid-state fluorescence performance of Zn-CP shows that compared with free H3IDC ligand, its fluorescence intensity is significantly enhanced.

Syntheses and structures of two benzoyl amides: 2-chloro-4-ethoxy-3,5-dimethoxy-N-(3-oxocyclohex-1-en-1-yl)benzamide and 2-chloro-N-(5,5-dimethyl-3-oxocyclohex-1-en-1-yl)-4-ethoxy-3,5-dimethoxybenzamide

The first title benzoyl amide, C17H20ClNO5 (3a), crystallizes in the monoclinic space group P21/c with Z = 4 and the second, C19H24ClNO5 (3b), also crystallizes in P21/c with Z = 8 (Z′ = 2), thus there are two independent molecules in the asymmetric unit. In 3a, the phenyl ring makes a dihedral angle of 50.8 (3)° with the amide moiety with the C=O group on the same side of the molecule as the C—Cl group. One methoxy group is almost in the plane of the benzene ring, while the ethoxy and other methoxy substituent are arranged on opposite sides of the ring with the ethoxy group occupying the same side of the ring as the C=O group in the amide moiety. For one of the two molecules in 3b, both the amide and 5,5-dimethyl-3-oxocyclohex-1-en-1-yl moieties are disordered over two sets of sites with occupancies of 0.551 (2)/0.449 (2) with the major difference between the two conformers being due to the conformation adopted by the cyclohex-2-en-1-one ring. The three molecules in 3b (i.e., the undisordered molecule and the two disorder components) differ in the arrangement of the subsituents on the phenyl ring and the conformation adopted by their 5,5-dimethyl-3-oxocyclohex-1-en-1-yl moieties. In the crystal of 3a, N—H...O hydrogen bonds link the molecules into a zigzag chain propagating in the [001] direction. For 3b a combination of C—H...O and N—H...O intermolecular interactions link the molecules into a zigzag ribbon propagating in the [001] direction.

Slow dynamics of disordered zigzag chain molecules in layered LiVS2 under electron irradiation

Electronic instabilities in transition metal compounds often spontaneously form orbital molecules, which consist of orbital-coupled metal ions at low temperature. Recent local structural studies utilizing the pair distribution function revealed that preformed orbital molecules appear disordered even in the high-temperature paramagnetic phase. However, it is unclear whether preformed orbital molecules are dynamic or static. Here, we provide clear experimental evidence of the slow dynamics of disordered orbital molecules realized in the high-temperature paramagnetic phase of LiVS2, which exhibits vanadium trimerization upon cooling below 314 K. Unexpectedly, the preformed orbital molecules appear as a disordered zigzag chain that fluctuate in both time and space under electron irradiation. Our findings should advance studies on soft matter physics realized in an inorganic material due to disordered orbital molecules.

Crystal Structure and Magnetic Properties of the Magnetically Isolated Zigzag Chain in KGaCu(PO4)2

Magnetism of any material depends on its crystal structure. However, two isostructural compounds such as MCuMoO4(OH) (M = Na, K) can have markedly different magnetic properties. Herein, we introduce a...

Coordination Polymers Constructed from Semi-Rigid N,N′-Bis(3-pyridyl)terephthalamide and Dicarboxylic Acids: Effect of Ligand Isomerism, Flexibility, and Identity

Reactions of the semi-rigid N,N′-bis(3-pyridyl)terephthalamide (L) with divalent metal salts in the presence of dicarboxylic acids afforded [Cd(L)0.5(1,2-BDC)(H2O)]n (1,2-H2BDC = benzene-1,2-dicarboxylic acid), 1, {[Cd(L)1.5(1,3-BDC)(H2O)]·5H2O}n (1,3-H2BDC = benzene-1,3-dicarboxylic acid), 2a, {[Cd(1,3-BDC)(H2O)3]·2H2O}n, 2b, {[Cd(L)0.5(1,4-BDC)(H2O)2]·H2O}n (1,4-H2BDC = benzene-1,4-dicarboxylic acid), 3, and [Cu(L)0.5(5-tert-IPA)]n (5-tert-IPA = 5-tert-butylbenzene-1,3-dicarboxylic acid), 4, which have been structurally characterized by single crystal X-ray diffraction. Complexes 1 and 3 are two-dimensional (2D) layers with the bey and the hcb topologies, and 2a and 2b are one-dimensional (1D) ladder and zigzag chain, respectively, while 4 shows a 3-fold interpenetrated three-dimensional (3D) net with the cds topology. The structures of these coordination polymers containing the semi-rigid L ligands are subject to the donor atom positions and the identity of the dicarboxylate ligands, which are in marked contrast to those obtained from the flexible bis-pyridyl-bis-amide ligands that form self-catenated nets. The luminescence of 1 and 3 and thermal properties of complexes 1, 3, and 4 are also discussed.