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

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) angstrom, a = 97.49( 3), beta = 109.64( 3) and gamma = 101.99(3)degrees. 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) angstrom, a = 77.41( 3), beta = 88.78( 3) and gamma = 88.16(3)degrees. 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) angstrom, alpha = 75.93( 3), beta = 82.88( 3) and gamma = 79.00( 3)degrees for 3 and a = 9.2692( 19), b = 15.369( 3), c = 18.353( 4) angstrom, alpha = 75.37( 3), beta = 81.32( 3) and gamma = 78.15( 3)degrees 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.