Nitro-functionalization and quantum yield of emission of Eu(III) and Tb(III) benzoic acid complexes

Abstract

In our pursuit of luminescent lanthanide ion-based coordination polymers, we have isolated several complexes with nitrobenzoic acid ligands and characterized these by X-ray crystallography and luminescence spectroscopy. 2-Nitrobenzoic acid reacts with Eu(III) to form 1, which crystallizes in the P-1 space group, with a = 12.385(3), b = 12.912(3), c = 17.889(4) Å, α = 97.49(3), β = 109.64(3) and γ = 101.99(3)°. 3-Nitrobenzoic acid forms a one-dimensional coordination polymer with Eu(III), 2, which crystallizes in the triclinic space group P-1 with a = 9.7100(19), b = 10.579(2), c = 13.361(3) Å, α = 77.41(3), β = 88.78(3) and γ = 88.16(3)°. Structures 3 and 4 correspond to the isostructural one-dimensional coordination polymers of Eu(III) and Tb(III), respectively, with the 4-nitrobenzoato anion. These crystallize in the triclinic space group P-1 with a = 9.2242(18), b = 15.102(3), c = 18.587(4) Å, α = 75.93(3), β = 82.88(3) and γ = 79.00(3)° for 3 and a = 9.2692(19), b = 15.369(3), c = 18.353(4) Å, α = 75.37(3), β = 81.32(3) and γ = 78.15(3)° for 4. Potentiometry, absorption and NMR spectroscopy indicate that in solution only 1 : 1 species are present. All compounds are weakly luminescent as solids and the photophysics of solutions of ligands with Ln(III) in 1 : 1 stoichiometry were studied. Quantum yields around 1 and 3% for Eu(III)-and Tb(III)-containing methanolic solutions were measured.