Synthesis, Crystal Structures and DFT Calculations of Two Schiff Base Derivatives of (2-Amino-5-ethyl-thiophen-3-yl)-(2-chloro-phenyl)-methanone

Two new Schiff base derivatives of (2-amino-5-ethyl-thiophen-3-yl)-(2-chloro-phenyl)-methanone, namely C 22 H 19 N 2 O 5 SCl ( I ) and C 20 H 15 N 2 O 3 SCl ( II ), have been synthesized and characterized by means of NMR, single-crystal X-ray diffraction and density functional theory geometry optimization and molecular orbital calculations. Compound ( I ) crystallizes in the triclinic space group P-1, with a = 7.8235(6) Å, b = 10.3256(5) Å, c = 13.6678(9) Å, α = 82.597(5)°, β = 74.759(6)°, γ = 89.968(5)°, V = 1055.96(12) Å 3 and Z = 2. Compound ( II ) also crystallizes in the triclinic space group P-1, with a = 8.0644(7) Å, b = 10.7984(9) Å, c = 10.8191(9) Å, α = 104.142(7)°, β = 92.660(7)°, γ = 93.292(7)°, V = 910.31(13) Å 3 and Z = 2. Geometry optimization calculations for each compound support these observations. Both compounds display R 2 2 (10) ring motifs formed by weak C···H···O intermolecular interactions and contribute to crystal packing. Additionally, the frontier molecular orbitals of each complex are displayed and correlation between the calculated molecular orbital energies (eV) for the surfaces of the frontier molecular orbitals to the electronic excitation transitions from the absorption spectra has been proposed. Graphical Abstract Synthesis, crystal structures, density functional theory (DFT) geometry optimization and molecular orbital surface calculations of two new Schiff base derivatives of (2-amino-5-ethyl-thiophen-3-yl)-(2-chloro-phenyl)-methanone: (2-chloro-phenyl)-{2-[(4,5-dimethoxy-2-nitro-benzylidene)-amino]-5-ethyl-thiophen-3-yl}-methanone, ( I ): C 22 H 19 N 2 O 5 SCl and (2-chloro-phenyl)-{5-ethyl-2-[(4-nitro-benzylidene)-amino]-thiophen-3-yl}-methanone ( II ): C 20 H 15 N 2 O 3 SCl.