First X-ray structural characterization of isatin Schiff base derivative. NMR and theoretical conformational studies

•X-ray structure of isatin Schiff base derivative E-isomer determined.•E/Z ratio in different solvents investigated by NMR spectroscopy.•Conformational analysis was performed by theoretical methods.

Isatin (1H-indole-2,3-dione) is an endogenous natural compound under intense development in medicinal chemistry. Here, we characterize isatin Schiff base derivative by X-ray crystallography. We describe a derivative that crystallizes E  -isomer form in the triclinic space group P 1¯;a = 5.9580 (4) Å, b = 8.4184 (7) Å, c = 14.1801 (14) Å, α = 73.962 (8)°, β = 83.184 (7)°, γ = 81.143 (6)°. NMR data show that E-conformer interconverts to the Z-conformer when dissolved, this equilibrium weakly depends on the solvent type. The Z-isomer geometry and the energetics of ΔEE–Z interconversion barriers were determined by quantum chemical calculations. The isomers are further characterized by means of FT-IR and UV–Vis spectroscopy.