Optical properties of lanthanide squarates

Two types of lanthanide squarate hydrates of formulae Eu(C4O4)(HC4O4)(H2O)6·H2O (compound I) and Ln2(C4O4)3(H2O)8 where Ln = Eu and Gd (compound II) were investigated. The optical properties of crystals I and selected spectral data for compound II are reported and confronted with earlier studies of europium complexes type II. Excitation and emission spectra were measured at 77 K. Effect of polymeric structure on spectroscopic properties is considered and correlated with structural data. Cooperative intrachain interactions between metal ions coupled via squarate anions were pointed and cooperative absorption was recorded. To check the presence of the Eu2+ traces, the EPR and γ-irradiation measurements were applied. Raman spectra of the compound II (where Ln = from Sm to Lu) were measured in the range of 50-500 cm-1. Positions of the bands were considered in function of ionic radius of lanthanide ion. The above, together with the data from excitation spectra, allows to localize the Ln-O bands. Vibronic components in electronic spectra were elucidated and assigned. (author)