Crystal Structure of 2-((E)-((Z)-3-(((4-hydroxyphenyl)amino)methylene)-4-oxocyclohexa-1,5-dien-1-yl)diazenyl)benzoic Acid and Synthesis, Spectroscopy, and DFT Study of Its Dibutyltin(IV) Complex

The structure of the 2-((E)-((Z)-3-(((4-hydroxyphenyl)amino)methylene)-4-oxocyclohexa-1,5-dien-1-yl)diazenyl)benzoic acid (H₃L) was confirmed by single crystal X-ray diffraction and Hirshfeld surface analysis was used further to quantify the intermolecular interactions. It crystallized in monoclinic space group P2₁/c. The observed bond distances evidence that the structure exists predominately in azo-enamine tautomeric form in the solid state. A novel dibutyltin(IV) complex, [(Bu₂SnHL)₂] (1) was synthesized from H₃L. The complex was then characterized by studying different techniques including elemental analysis, FT-IR, and NMR (¹H, ¹³C, and ¹¹⁹Sn) spectroscopy. In solution state, the molar mass of the compound was confirmed by Mass spectrometry. Spectroscopy study guides to predict the structure of the complex which is supposed to be a cyclic dimer [(Bu₂SnHL)₂] and Sn(IV) adopts a six-coordinated geometry. However, in solution Sn(IV) adopts four coordinated distorted tetrahedral geometry which was supported by ¹¹⁹Sn NMR spectroscopy (δ_Sn(119), 126.34 ppm) and EI-MS results of the complex ion ([C₂₈H₃₂N₃O₄Sn]⁺,m/z 593.1). Further, the structures in solid and solution state were supported by developing their optimized structures and IR data from the DFT calculation.

Graphical Abstract

The crystal structure of the ligand is in azo-enamine tautomeric form and in accordance with DFT study, its dibutyltin(IV) complex is a cyclic dimer, (Bu₂SnHL)₂, which becomes monomer in solution.