Crystal structure and optical properties of a two-sited Eu^IIIcompound: an Eu^IIIion coordinated by two [Eu^III(DOTA)]⁻complexes (DOTA is 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetate)

Abstract

The structure and solid-state luminescence properties of an EuIII compound with two different lanthanide sites, [Eu(μ-O)5(OH)(H2O)2][Eu(DOTA)(H2O)]2 (DOTA is 1,4,7,10-tetrazacyclododecane-1,4,7,10-tetraacetate, C16H24N4O8), were determined. The compound crystallizes in a laminar structure in the triclinic space group P\overline{1}, where the two sites are a free europium(III) ion and an [Eu(DOTA)(H2O)]− complex. The crystal structure was determined using complex data treatment due to nonmerohedral twinning. Experimental data sets were recorded with large redundancy and separated according to scattering domains in order to obtain a reliable structure. In the first site, the [Eu(DOTA)(H2O)]− complex was found to adopt a capped twisted square-antiprismatic (cTSAP) conformation, where a capping water molecule increased the coordination number of the europium(III) site to nine (CN = 9). In the second site, the europium(III) ion was found to be coordinated by two water molecules, one hydroxide group and five oxide groups from neighbouring [Eu(DOTA)(H2O)]− complexes. The coordination geometry of this site was found to be a compressed square antiprism (SAP) and the coordination number of the europium(III) ion was found to be eight (CN = 8). A large increase in the rate constant of luminescence was observed for EuIII in [Eu(DOTA)(H2O)]− in solid-state luminescence spectroscopy measurements compared to in solution, which led to investigations of single crystals in deuterated media to exclude additional effects of quenching. We conclude that the most probable cause of the decrease in the observed luminescence lifetimes is the high asymmetry of the coordination environment of [Eu(DOTA)(D2O)]− in the [Eu(μ-O)5(OD)(D2O)2][Eu(DOTA)(D2O)]2 crystals.

Long story short: donor set symmetry in [Eu(DOTA)(H2O)]−crystals determines the electronic structure

“…The observed luminescence lifetimes were determined from a single-exponential fit to the data as τ ( 1 ) = 643 μs, τ ( 2 ) = 755 μs, and τ ( 3 ) = 850 μs. This supports the conclusion of just a single emitter in the crystal, 30 and that we see no influences from surface sites or other imperfections, but no further conclusions can be drawn due to the differences in the pathways of non-radiative deactivation in the three compounds.…”

“…22,27 In both Gd[DOTA] − and [Eu(DOTA)(H 2 O)] − , the cSAP form dominates, and most crystal structures are of this form of the complex. 27–30…”

“…22,27 In both Gd[DOTA] − and [Eu(DOTA)(H 2 O)] − , the cSAP form dominates, and most crystal structures are of this form of the complex. [27][28][29][30] In solution all eight forms must be considered (four with capping water molecules and four without), 21 and all experiments must be considered to be reporting on all forms. 31,32 Thus, building direct structure-property relationships requires studies of crystalline systems.…”

Arel: Investigating [Eu(H2O)9]3+ Photophysics and Creating a Method to Bypass Luminescence Quantum Yield Determinations

“…This treatment is problematic as there is no photophysical rationale for the transition probabilities of the states within the S L J manifold to be equal. This is clear when high resolution is achieved as bands often split into peaks of varying intensity. ,, When this level of detail is not achievable, care should be taken when rationalizing based on transition probabilities and branching ratios of bands instead of the actual transition lines. For all lanthanide­(III) ions bar europium­(III) this becomes a significant challenge as each band contains numerous lines.…”

Long Story Short: Donor Set Symmetry in Eu(DOTA) Crystals Determines the Electronic Structure

“…In Gd.DOTA and Eu.DOTA the cSAP form dominates, and most crystal structures are for this form of the complex. [27][28][29][30] In solution all eight forms must be considered, 21 and all experiments must be considered to be reporting on all forms. 31,32 Thus, building direct structure-property relationships requires studies of crystalline systems.…”