2-Amidoindole-based anion receptors

Abstract

Four receptors containing either 2-amidoindole or 7-nitro-2-amidoindole groups have been synthesised and shown to complex oxoanions in DMSO-d ₆/0.5% water solution. X-ray crystal structure elucidation reveals that receptor 1 complexes dihydrogen phosphate ion pairs in the solid state, which are part of a continuous chain. While this receptor binds dihydrogen phosphate in a 1:1 stoichiometry in solution, compound 4, which contains 7-nitroindole groups, does form 1:2 receptor:dihydrogen phosphate complexes in DMSO-d ₆/0.5% water.

Keywords:

• anion binding
• indole
• hydrogen bonding
• crystallography

Acknowledgements

We thank the EPSRC for studentship funding (JRH) and for access to the crystallographic facilities at the University of Southampton. CC would like to thank Regione Sardegna for a Master & Back grant.

Notes

^1. Crystal data for compound 1· tetrabutylammonium dihydrogen phosphate CCDC 686083: C₅₅H₁₀₀N₆O₁₀P₂, Mr = 1067.35, T = 120(2) K, triclinic space group , a = 14.4568(8), b = 14.5325(8), c = 16.3506(8) Å, α = 108.932(2)°, β = 104.053(2)°, γ = 98.051(2)°, V = 3061.1(3) Å³, ρ_calc = 1.158 Mg/m³, μ = 0.128 mm^− 1, Z = 2, reflections collected: 34256, independent reflections: 10399 [R _int = 0.0662], final R indices [I>2σI]: R ₁ = 0.1248, wR ₂ = 0.3162, R indices (all data): R ₁ = 0.1518, wR ₂ = 0.3381.

^2. Crystal data for compound 2√ tetrabutylammonium fluoride CCDC 690147: C₅₅H_99.50F₂N₈O_8.75, Mr = 1050.93, T = 120(2) K, triclinic space group , a = 18.2539(8), b = 19.4067(5), c = 20.2800(9) Å, α = 67.988(2)°, β = 83.891(2)°, γ = 63.829(2)°, V = 5962.7(4) Å³, ρ_calc = 1.171 Mg/m³, μ = 0.083 mm^− 1, Z = 4 reflections collected: 81556, independent reflections: 20977 [R _int = 0.1296], final R indices [I>2σI]: R ₁ = 0.1139, wR ₂ = 0.2830, R indices (all data): R ₁ = 0.2326, wR ₂ = 0.3566.