Synthesis, Crystal Structures and DFT Calculations of Three Schiff Base Derivatives of (2-Amino-4,5,6,7-tetrahydrobenzo[b]thiophen-3-yl)-phenylmethanone

Three new Schiff base derivatives of (2-amino-4,5,6,7-tetrahydrobenzo[b]thiophen-3-yl)-phenylmethanone, namely, C 23 H 21 NO 3 S (I) , C 24 H 22 N 2 O 5 S (II) and C 26 H 28 N 2 O 2 S (III) have been synthesized and characterized by NMR, single-crystal X-ray diffraction and DFT molecular orbital calculations. Compound (I) crystallizes in the orthorhombic space group P 2 1 2 1 2 1 , with Z = 4 in cells with a = 5.02536(8) Å, b = 17.5927(3) Å, c = 21.2134(4) Å, V = 1875.47(5) Å 3 and displays weak C–H···O intermolecular interactions which contribute to crystal packing. Compound (II) crystallizes in the monoclinic space group P 2 1 / c , with Z = 4 in cells with a = 11.2263(2) Å, b = 19.7401(3) Å, c = 10.0202(2) Å, β = 108.565(2)°, V = 2105.00(8) Å 3 and displays weak C–H···O intermolecular interactions forming zig-zag chains along the b axis and weak π–π stacking interactions which influence crystal packing. Compound (III) also crystallizes in the monoclinic space group P 2 1 / c , with Z = 4 in cells with a = 10.9599(2) Å, b = 11.9287(3) Å, c = 17.0626(4) Å, β = 97.680(2)°, V = 2210.71(8) Å 3 and displays weak C–H···O intermolecular interactions which contribute to crystal packing. Additionally, the DFT frontier molecular orbitals of each compound 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 of each compound has been proposed. Graphical Abstract Synthesis, crystal structures, density functional theory (DFT) and molecular orbital surface calculations of three new Schiff base derivatives of (2-amino-4,5,6,7-tetrahydrobenzo[b]thiophen-3-yl)-phenylmethanone: {2-[(2-hydroxy-3-methoxy-benzylidene)-amino]-4,5,6,7-tetrahydrobenzo[b]thiophen-3-yl}-phenylmethanone (I): C 23 H 21 NO 3 S; {2-[(4,5-dimethoxy-2-nitro-benzylidene)-amino]-4,5,6,7-tetrahydrobenzo[b]thiophen-3-yl}-phenylmethanone, (II): C 24 H 22 N 2 O 5 S and {2-[(4-diethylamino-2-hydroxybenzylidene)-amino]-4,5,6,7-tetrahydrobenzo[b]thiophen-3-yl}-phenylmethanone, (III): C 26 H 28 N 2 O 2 S.