The study of interactions with a halogen atom: influence of NH2 group insertion on the crystal structures of meta-bromonitrobenzene derivatives

New O- and N-N-Bridging Complexes of Tc(V), the Role of the Nitrogen Atom Position in Aromatic Rings: Reaction Mechanism, Spectroscopy, DTA, XRD and Hirshfeld Surface Analysis

In this work, O- and N-N-bridging complexes of technetium (V), previously known only for rhenium, were obtained for the first time. Tc(V) complexes with pyridazine (pyd), 1,2,4-triazole (trz), 3,5-dimethylpyrazole (dmpz) and pyrimidine (pyr) were obtained. In three complexes [{TcOCl₂}₂(μ-O)(μ-pyd)₂], [{TcOCl₂}₂(μ-O)(μ-trz)₂]·Htrz·Cl and [{TcO(dmpz)₄}(μ-O)(TcOCl₄)] two technetium atoms are linked by a Tc-O-Tc bond, and in the first two, Tc atoms are additionally linked by a Tc-N-N-Tc bond through the nitrogen atoms of the aromatic rings. We determined the role of nitrogen atom position in the aromatic ring and the presence of substituents on the formation of such complexes. For the first time, a reaction mechanism for the formation of such complexes was proposed. This article details the crystal structures of four new compounds. The work describes in detail the coordination of Tc atoms in the obtained structures and the regularities of the formation of crystal packings. The spectroscopic properties of the obtained compounds and their mother solutions were studied. The decomposition temperatures of the described complexes were determined. An assumption was made about the oligomerization of three-bridged complexes based on the results of mass spectrometry. Through the analysis of non-valent interactions in the structures, π-stacking, halogen-π and CH-π interactions were found. An analysis of the Hirshfeld surface for [{TcOCl₂}₂(μ-O)(μ-pyd)₂], [{TcOCl2}2(μ-O)(μ-trz)₂] and their rhenium analogues showed that the main contribution to the crystalline packing is made by interactions of the type Hal···H/H···Hal (45.4-48.9%), H···H (10.2-15.8%), and O···H/H···O (9.4-16.5%).

Novel Synthesis Methods of New Imidazole-Containing Coordination Compounds Tc(IV, V, VII)-Reaction Mechanism, Xrd and Hirshfeld Surface Analysis

In this work, we have proposed two new methods for the synthesis of [TcO₂L₄]⁺ (where L = imidazole (Im), methylimidazole (MeIm)) complexes using thiourea (Tu) and Sn(II) as the reducing agents. The main and by-products of the reactions were determined, and possible reaction mechanisms were proposed. We have shown that the reduction of Tc(VII) with thiourea is accompanied by the formation of the Tc(III) intermediate and further oxidation to Tc(V). The reaction conditions’ changing can lead to the formation of Tc(VII) and Tc(IV) salts. Seven new crystal structures are described in this work: Tc(V) complexes, salts with Tc(VII) and Tc(IV) anions. For the halide salts of Tu the cell parameters were determined. In all of the obtained compounds, except for [TcO₂(MeIm)₄]TcO₄, there are π–stacking interactions between the aromatic rings. An increase in the anion size lead to weakening of the intermolecular interactions. The halogen bonds and anion-π interactions were also found in the hexahalide-containing compounds. The Hirshfeld surface analysis showed that the main contribution to the crystal packing is created by the van der Waals interactions of the H···H type (42.5–55.1%), H···C/C···H (17.7–21.3%) and hydrogen bonds, which contribute 15.7–25.3% in total.

Synthesis, Crystal Structure, and Hirshfeld Surface Analysis of Hexachloroplatinate and Tetraclorouranylate of 3-Carboxypyridinium—Halogen Bonds and π-Interactions vs. Hydrogen Bonds

This work aimed to synthesize new platinum and uranium compounds with nicotinic acid. In this article we describe the synthesis of two new anionic complexes (HNic)2[PtCl6] and (HNic)2[UO2Cl4] using wet chemistry methods. The structure of the obtained single crystals was established by single-crystal X-ray diffraction. The Hirshfeld surface analysis of the obtained complexes and their analogue (HNic)2[SiF6] was carried out for the analysis of intermolecular interactions. Hydrogen bonds (H···Hal/Hal···H and O···H/H···O) make the main contribution to intermolecular interactions in all compounds. Other important contacts in cations in all compounds are H···H, C···H/H···C and C···Hal/Hal···C; in anions H···Hal/Hal···H. The Pt-containing complex has a halogen-π interaction and halogen bonds, but Si-containing complex has a π–π staking interaction; these types of interactions are not observed in the U-containing compound.

Structural, theoretic and spectroscopic analysis of 2-methyl-5-nitroaniline salts with various inorganic acids

Crystal structures of six new salts of 2-methyl-5-nitroaniline with inorganic acids [(H2Me5NA)Br, (H2Me5NA)I, (H2Me5NA)NO₃, (H2Me5NA)Cl, (H2Me5NA)HSO₄ and (H2Me5NA)I₃·0.5H₂O] are determined by single-crystal X-ray diffraction. The most important hydrogen-bonding patterns are formed by the ammonio group and respective anions composing 1D or 2D networks. The patterns are analysed using the graph-set approach and mathematical interrelations between graph-set descriptors are shown for comparative purposes. Analysis of IR spectra enables the strength of hydrogen bonds in the crystals to be assessed. The frequency of N-H and O-H stretching vibrations and NH₃ group libration indicates that the strongest hydrogen bonds are present in (H2Me5NA)HSO₄, whereas the weakest ones occur in (H2Me5NA)I₃·0.5H₂O. Hirshfeld surface analysis reveals that apart from obvious N-H...anion hydrogen bonds, the molecules are also connected to each other by exclusive C-H...O_NO2 interactions. The opposite occurs in the crystal structure of 2-methyl-4-nitroaniline salts, where a variety of O_NO2...π(N)_NO2 non-hydrogen bonding interactions are observed.