Spontaneous resolution of a novel chiral coordination polymer through supramolecular interactions and solvent symmetry breaking

Abstract

The spontaneous resolution reaction of racemic trans-2,3-dihydro-2,3-dipyridyl-benzo[ e]indole 1 with Cd(ClO 4) 2·6H 2O in the presence of 2-butanol under solvothermal reaction conditions favors the formation of crystal 2 [ P-Cd( R, R,- 1) 2(ClO 4) 2], while a similar reaction in the presence of ethanol only favors the formation of crystal 3 [ M-Cd( S, S,- 1) 2(ClO 4) 2]. The crystal structural determination shows that both 2 and 3 crystallize in chiral enantiomorphous space groups ( P6 122 and P6 522) and their structures are 1D infinite chain, and are just enantiomorphous pairs most like. The spontaneous resolution process displays estimated ee values of ca. +0.6 for 2-butanol and ca. −0.4 for ethanol. Enantiomerically pure ( S, S)- trans-2,3-dihydro-2,3-dipyridyl-benzo[ e]indole ( S, S,- 1) can be obtained through the decomposition of mechanically separated 3. Additionally ( S, S,- 1) also crystallizes in a chiral space group ( P2 1). The CD (circular dichroism) spectra of both 2 and 3 in the solid state are also approximately enantiomorphous pairs. However, their fluorescent spectra in the solid state display a moderate difference in maximum emission peaks (Δ λ = 19 nm). Crystal data for 2: C 44H 34Cl 2N 6O 8Cd, M = 958.07, hexagonal, P6 122, a = 10.5488(5), c = 68.256(4) Å, α = γ = 90°, β = 120°, V = 6577.8(6) Å 3, Z = 6, D c = 1.451 mg m −3, R 1 = 0.0498, wR 2 = 0.1124, μ = 0.679 mm −1, S = 0.623, Flack χ = −0.02(6). For space group P6 522, R 1 = 0.0670, wR 2 = 0.1602, S = 0.725 with a Flack value of 1.03(7); Crystal data for 3, C 44H 34Cl 2N 6O 8Cd, M = 958.07, hexagonal, P6 522, a = 10.5446(3), c = 68.265(3) Å, V = 6573.3(4) Å 3, Z = 6, D c = 1.452 mg m −3, R 1 = 0.0444, wR 2 = 0.1002, μ = 0.679 mm −1, S = 0.558, Flack χ = 0.01(5). For space group P6 122, R 1 = 0.0501, wR 2 = 0.1178, S = 0.599 with a Flack value of 1.00(5). The low Flack parameter indicates that the absolute configurations of 2 and 3 are stated; Crystal data for ( S, S)- 1, C 22H 17N 2, M = 323.39, orthorhombic, P2 12 12 1, a = 9.2598(7), b = 9.4617(8), c = 19.1452(16) Å, V = 1677.4(2) Å 3, Z = 4, D c = 1.281 mg m −3, R 1 = 0.0417, wR 2 = 0.1191, T = 293 K, μ = 0.077 mm −1, S = 0.862.