In recent years, a lot of attention has been devoted to monolayer materials, in particular to transition-metal dichalcogenides (TMDCs). While their growth on a substrate and their exfoliation are well developed, the colloidal synthesis of monolayers in solution remains challenging. This paper describes the development of synthetic protocols for producing colloidal WS2 monolayers, presenting not only the usual semiconducting prismatic 2H-WS2 structure but also the less common distorted octahedral 1T-WS2 structure, which exhibits metallic behavior. Modifications of the synthesis method allow for control over the crystal phase, enabling the formation of either 1T-WS2 or 2H-WS2 nanostructures. We study the factors influencing the formation of the two WS2 nanostructures, using X-ray diffraction, microscopy, and spectroscopy analytical tools to characterize them. Finally, we investigate the integration of these two WS2 nanostructured polymorphs into an efficient photocatalytic hydrogen evolution system to compare their behavior.

Organic molecules crystallize in manifold structures. The last few decades have seen the rise of high-resolution X-ray diffraction techniques that make the structures of even the most complex crystals easily accessible. Still, an intrinsic challenge lies in assigning hydrogen atoms’ positions from X-ray experiments alone. Quantum chemistry plays a fruitful, complementary role here, and so ab initio optimization techniques for organic crystals are on the rise as well. In this context, we review and evaluate a popular ab initio strategy based on plane-wave density-functional computations, namely, selectively relaxing H positions in an otherwise fixed cell. Our data show that such-optimized C–H, N–H, O–H, and B–H bond lengths coincide well with results from neutron diffractionthe experimental technique that sets the “gold standard” for H positions in molecular crystals but which is far less easily available. We have thus justified the use of a quantum-chemical aide with a broad variety of possible applications.

Rubidium guanidinate, RbCN(3)H(4), was synthesized from guanidine and rubidium hydride, and the crystal structure was determined from powder X-ray diffraction (PXRD) data. RbCN(3)H(4) crystallizes in the orthorhombic space group Pnma (No. 62) with four formula units per cell. The guanidinate anions are arranged in double chains running along the b axis, stacked almost perpendicularly to each other to form a three-dimensional network. The rubidium cations, coordinated by 11 N atoms, occupy the vacancies of the network in a zigzag motif along the b axis. Because the PXRD structure of the CN(3) core clearly indicates the N-atom functionalities and the location of the H-atom positions, the latter spatial parameters were determined from Perdew-Burke-Ernzerhof generalized gradient approximation (GGA-PBE) density functional theory calculations. The corresponding ν(NH) stretching modes can be observed in the IR spectrum, and the volume chemistry of RbCN(3)H(4) mirrors the efficient packing of the saltlike phase.

Hydrogen bonding is among the most important interactions in molecular crystals, and examples are abundant. As a consequence of such interactions, many molecules crystallize in complex but intriguing structures, in contrast to the relatively simple packing principles of metallic or ionic solids. In this work, we present a computational approach based on plane-wave density-functional theory (DFT) and supercell techniques, aiming to understand and quantify hydrogen-bonded networks in the solid state and in two-, one-, and zero-dimensional fragments derived from the molecular crystal. With such methodology at hand, we investigate guanidine, a fitting example of a molecular crystal and an important compound for inorganic and organic chemistry alike. On the basis of our computations, we discuss the initially proposed layered structure of guanidine and identify both stabilizing and destabilizing cooperative interactions in the three crystalline dimensions.

Nanorods of triniobium hydroxide heptaoxide, Nb3 O7 (OH), were synthesized by means of a hydrothermal method. Subsequently, Pt and CuO nanoparticles were introduced on the surface of Nb3 O7 (OH) nanorods by a microwave-assisted solvothermal nucleation and growth technique. The resulting Pt- and CuO-decorated Nb3 O7 (OH) nanorods demonstrated uniform particle dispersion and were fully characterized by X-ray diffraction, electron microscopy, and spectroscopic analysis. Furthermore, the solar-powered photocatalytic hydrogen production properties of these heteronanostructures were studied. The solar-driven H2 formation rate over Pt-Nb3 O7 (OH) was determined to be 710.4 ± 1.7 μmol g(-1) h(-1) with a quantum efficiency of ϕ=5.40% at λ=380 nm. Interestingly, the as-prepared CuO-Nb3 O7 (OH) heteronanostructure was found to be inactive under solar irradiation during an induction phase, whereupon it undergoes an in situ photoreduction process to form the photocatalytically active Cu-Nb3 O7 (OH). This restructuring process was monitored by an in situ measurement of the time-evolution of the optical absorption spectra. The solar-powered H2 production for the restructured compound was determined to be 290.3 ± 5.1 μmol g(-1) h(-1) .