Crystal Structure and Optical Properties of a Homometallic Heterotrinuclear Europium(III) Complex – a Cationic Eu(III) ion Coordinated by two [Eu(III)DOTA]- Complexes

The structure and solid state luminescence properties of a homometallic heterotrinuclear [Eu(μO)5(OH2)3][Eu(DOTA)(H2O)]2Cl crystal was determined and was found to have two sites: a free europium(III) ion and a [Eu(DOTA)(H2O)]- complex. The trinuclear compound crystallizes in a laminar structure in triclinic space group P. The crystal structure was determined using complex data treatment due to non-merohedric twinning. Experimental data sets were recorded with large redundancy and separated according to scattering domain in order to obtain a reliable structure, which revealed the configuration of the europium(III) sites. In first site, the europium(III) 1,4,7,10-tetrazacyclododecane-1,4,7,10-tetraacetate (Eu.DOTA) 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 cationic europium(III) ion was found to be coordinated by three water molecules and five oxy groups from neighboring [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 rate constant of luminescence was observed for Eu(III) in [Eu(DOTA)(H2O)]- in solid state luminescence spectroscopy measurements compared to in solution, which lead 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 observed luminescence lifetimes is the high asymmetry of the coordination environment of [Eu(DOTA)(D2O)]- in the [Eu(μO)5(OD2)3][Eu(DOTA)(D2O)]2Cl crystals