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

Abstract

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%).

Thiourea as a Stabilizer of Reduced Forms of Technetium─Tc(III) and Tc(IV): Experimental and Theoretical Studies of Complexes

“…Weak intermolecular interactions are of particular interest from a theoretical point of view; the study of such interactions in pertechnetates and perrhenates of purines led to the discovery of a new type of chemical bond. , New methods of separating perrhenates and pertechnetates are based on nonvalent interactions. − The study of the contribution of the nonvalent interactions for various technetium compounds will allow a deeper understanding of the impact of radiopharmaceuticals on living organisms and of the formation of nontrivial technetium complex compounds, similar to those described in refs , − . Information about weak interactions can also be useful for predicting the behavior of Tc-containing intermediates in catalytic and sorption processes on complex organic sorbents like those described …”

Intramolecular Re···O Nonvalent Interactions as a Stabilizer of the Polyoxorhenate(VII)

“…Absorption in the long-wavelength region of the spectrum can be associated with the formation of a solid dispersed phase in solution. The colloid presumably hydrated with TcO 2 can be both a product of the hydrolysis of Tc­(IV) compounds and disproportionation reactions of the formed Tc­(V) compounds that resemble those mentioned in refs and . It is likely that the medium’s high acidity (pH = 1–2) and the pertechnetate anion’s strong oxidative activity both prevent the synthesis of polyoxotechnetates.…”

The influence of the alkoxy substituent length on the crystal structures of Tc(v) complexes with pyrazine

“…In 3, for example, there is a short contact of the type C⋯Cl, but it cannot be called a Cl-π interaction due to the α angle being less than 50°. [49][50][51] In 2, 4, 6, 8 and 10 there are CH-πinteractions, 20,52 and in 8 and 10 O-π interactions. 50,53 However, despite the variety of non-covalent interactions, the main binding of molecules of the complexes into a structure occurs due to hydrogen bonds.…”

“…25 Understanding the role of non-covalent interactions in compounds of technetium(V) with an alkoxy substituent and the effect of the substituent size on them can be used to predict the behavior of radiopharmaceuticals in living organisms. 3,15,20 For further research, quantum chemical calculations and the discovery of new types of intermolecular interactions in crystals, accurate information about the structure of complexes of any type is required. [26][27][28] Noncovalent interactions, hydrogen bonds in particular, are used to separate perrhenates and pertechnetates.…”