Natalya A. Kryuchkova

Two sets of co-formers, polyfluorinated arylenediamines with variable structural elements and macrocyclic ethers of different sizes, were used to study the patterns of self-assembly of co-crystals and to rank the intermolecular interactions. The co-crystallization stoichiometry was found to increase from 1 : 1 to 2 : 1 in the series trifluoro-1,3-phenylenediamine, 2,4-diaminotrifluoropyridine, and 2,4-diaminotrifluoronitrobenzene and with decreasing crown ether size due to restructuring of guest–host interactions and forming guest–guest interactions. 18-Crown-6 and 15-crown-5 ethers form the typical N–H⋯O_cr H-bonds connecting two O_cr atoms with one bifunctional proton donor NH₂; when going to 12-crown-4, two O_cr atoms become connected with the H_amino atoms of two arylenediamine molecules. Modes of guest–guest bonding and supramolecular motifs in 2 : 1 co-crystals are determined by HB acceptors and p + π systems in arylenediamine: o-N–H⋯N_het and p-N–H⋯F interactions form face-to-face dimers united in a chain; p-N–H⋯O_nitro and o-N–H⋯O_nitro contacts generate head-to-tail and head-to-side chains; π⋯π and X⋯π (X = F, O, N) electron interactions form off-set stacks. Quantum chemical calculations reveal an increase of the packing enthalpies and bonding energies with increasing arylenediamine electron affinity and crown ether size. According to MEP, BCP and NCI analyses, these effects are caused either by strengthening of the interactions due to a greater electrostatic contribution, or by multiplying bonding contacts. Quantifying the interactions allowed us to identify the key supramolecular synthons and related elements of the co-former structure, which can serve as tools in the molecular crystal design.

The thermal behaviour of Ag₂[PtCl₄] and Ag₂[PtCl₆] complex salts in inert and reducing atmospheres has been studied. The thermolysis of compounds in a helium atmosphere is shown to occur in two stages. At the first stage, the complexes decompose in the temperature range of 350–500 °C with the formation of platinum and silver chloride and the release of chlorine gas. At the second stage, silver chloride is sublimated in the temperature range of 700–900 °C, while metallic platinum remains in the solid phase. In contrast to the thermolysis of Ag₂[PtCl₆], the thermal decomposition of Ag₂[PtCl₄] at 350 °C is accompanied by significant heat release, which is associated with disproportionation of the initial salt to Ag₂[PtCl₆], silver chloride, and platinum metal. It is confirmed by DSC measurements, DFT calculations of a suggested reaction, and XRD. The thermolysis of Ag₂[PtCl₄] and Ag₂[PtCl₆] compounds is shown to occur in a hydrogen atmosphere in two poorly separable steps. The compounds are decomposed within 170–350 °C, and silver and platinum are reduced to a metallic state, while a metastable single-phase solid solution of Ag_0.67Pt_0.33 is formed. The catalytic activity of the resulting nanoalloy Ag_0.67Pt_0.33 is studied in the reaction of CO total (TOX) and preferential (PROX) oxidation. Ag_0.67Pt_0.33 enhanced Pt nano-powder activity in CO TOX, but was not selective in CO PROX.

The work deals with the establishment of the dependence of the vibrational frequencies of strong O–H⋯O and N–H⋯O hydrogen bonds for the diagnosing the bonds themselves. To this end, the Raman spectra of a large number of different normal and deutero-substituted crystals characterized by the presence of strong O–H⋯O and N–H⋯O bonds are measured and the quantum chemical calculation is performed for one of these compounds. The dependence of the O–H stretching frequency on the O⋯O distance is constructed differing from that previously known for short O⋯O contacts. The mechanisms of significant broadening of the O–H vibration band in strong O–H⋯O hydrogen bonds are considered. Different dependences of the N–H vibrational frequencies in N–H⋯O bonds are reported and the causes of this diversity are discussed.