Flux Synthesis\nof Alkaline-Earth Lanthanide Borates\nas Potential Nuclear Waste Forms

Neodymium is typically considered\nthe best surrogate for trivalent\namericium and can be used to identify Am<sup>3+</sup> containing materials\nthat are likely to form. We have explored the alkaline-earth lanthanide\nborate phase space using alkaline-earth halide/carbonate fluxes. This\nresulted in the synthesis of new compounds AE<sub>5</sub>Ln(BO<sub>3</sub>)<sub>4</sub>X (AE = Ca, Sr; Ln = Pr, Nd, Eu, Tb; X = Cl,\nBr) and AE<sub>3</sub>Ln<sub>2</sub>(BO<sub>3</sub>)<sub>4</sub> (AE\n= Sr, Ba; Ln = Pr, Nd) as well as the synthesis of two compounds of\nBa<sub>8</sub>Ln<sub>2</sub>­(BO<sub>3</sub>)<sub>6</sub>(B<sub>2</sub>O<sub>5</sub>) (Ln = Eu, Tb) crystallizing in a new structure\ntype. Ba<sub>8</sub>Ln<sub>2</sub>­(BO<sub>3</sub>)<sub>6</sub>(B<sub>2</sub>O<sub>5</sub>) crystallizes in the space group <i>P</i>2<sub>1</sub>/<i>n</i> with lattice parameters <i>a</i> = 8.6002(3) Å, <i>b</i> = 7.9245(3) Å, <i>c</i> = 17.6697(7) Å, and β = 91.3560(10)° for\nthe Eu analogue, and the structure contains isolated LnO<sub>8</sub> polyhedra connected into a framework by BO<sub>3</sub> and B<sub>2</sub>O<sub>5</sub> units. The fluorescence emission spectra of\nAE<sub>5</sub>Ln­(BO<sub>3</sub>)<sub>4</sub>X (AE = Ca, Sr;\nLn = Eu, Tb; X = Cl, Br) and Ba<sub>8</sub>Ln<sub>2</sub>­(BO<sub>3</sub>)<sub>6</sub>(B<sub>2</sub>O<sub>5</sub>) (Ln = Eu, Tb) are\nreported.