Nine‐coordinated Eu3+ Dipicolinate Compounds: Different Crystal Structures and Luminescence Properties as a Function of pH

Abstract

AbstractTwo compounds, Na3[Eu(DPA)3] ⋅ 14H2O and [Eu(DPA)(HDPA)(H2O)2] ⋅ 4H2O, were created and the structure determined using single crystal X‐ray diffraction. The single crystal luminescence properties were compared and related to the Eu3+ coordination geometry. The formation of single crystals from solutions of Eu(CF3SO3)3 and H2DPA was found change with the pH value of the H2DPA solution. Mixtures of Na3[Eu(DPA)3] ⋅ 14H2O and [Eu(DPA)(HDPA)(H2O)2] ⋅ 4H2O were observed with a pH ratio between the two structures. While visual inspection showed that all samples contained both Na3[Eu(DPA)3] ⋅ 14H2O and [Eu(DPA)(HDPA)(H2O)2] ⋅ 4H2O, the PXRD and luminescence data did not immediately reveal that the samples were pure. Having discovered that the samples were indeed mixtures, quantification was attempted by Rietveld refinement of the PXRD data, and the luminescence spectra were compared to those from single crystals. As the data was not found to reveal that the samples were mixtures, even though we knew that this was the case, we must urge caution when inferring structure‐property relationships from powder samples. In this case we were able to isolate monophasic systems and do a comparative study, but this requires that the samples are identified as mixtures.