New aqua-fluoride and fluoride indium(III) complexes with monodentate-coordinated molecules of 4-amino-1,2,4-triazole. Synthesis, crystal structure, and thermogravimetry, DSC, and 19F,1H NMR study

Highlights: • The first In(III) complex with 4-amino-1,2,4-triazole molecules InF₃(H₂O)(C₂H₄N₄)₂ (I) was synthesized. • A thermal study showed that the formation of InF₃(C₂H₄N₄)₂ (II). • Structure I is formed from molecular complexes InF₃(H₂O)(C₂H₄N₄)₂. • Structure II is constructed from linear chains of compositions [InF₃(C₂H₄N₄)₂]. • Analysis of NMR data allowed us to identify types of ion mobility in I and II compounds. -- Abstract: A molecular aqua-fluoride complex of indium(III) InF₃(H₂O)(C₂H₄N₄)₂ (I) has been synthesized for the first time, along with its anhydrous analogue – InF₃(C₂H₄N₄)₂ (II), which has been obtained by thermal dehydration of I. The crystal structure of I is formed by molecular complexes [InF₃(H₂O)(C₂H₄N₄)₂] linked through O–H⋯F and N–H⋯F hydrogen bonds. The structure of the compound II appeared to be chainlike; linear chains of the composition ${}_{\infty }{}^1{\left[IN{F}_3{\left(C_2{H}_4{H}_4\right)}_2\right]}^0$ are formed as a result of linking the isolated molecules of the complexes I by In–F–In bridge bonds, in which vacancies of the removed H₂O molecules are occupied by F atoms of the neighboring molecules. The isolated chains are linked into a three-dimensional framework by N–H⋯F hydrogen bonds. In both compounds, In is coordinated by two neutral molecules of 4-amino-1,2,4-triazole. A distinctive feature of the InF₃(H₂O)(C₂H₄N₄)₂ compound is the presence of three different ligands in the coordination sphere of the indium atom: fluorine and, molecules of H₂O and 4-amino-1,2,4-triazole.The thermal behavior and character of ionic motions have been investigated by means of thermogravimetry (TG, DTG, DTA), DSC and ¹⁹F,¹H NMR spectroscopy.