Penta-potassium europium(III) dilithium deca-fluoride, K(5)EuLi(2)F(10).

The title compound, K(5)EuLi(2)F(10), belongs to so-called self-activated materials containing lanthanoid ions within the matrix. A common feature of these systems is a large separation between the closest lanthanoid ions, which is one of the crucial factors governing the self-quenching of luminescence. The crystal structure of K(5)EuLi(2)F(10) is isotypic with other K(5)RELi(2)F(10) compounds (RE = Nd, Pr). As expected from the lanthanoid contraction, the unit-cell volume for crystal with Eu(3+) ions is the smallest of the three structures. Accordingly, the corresponding inter-atomic RE-RE distances are shorter. In the structure, distorted EuF(8) dodeca-hedra and two different LiF(4) tetra-hedra, all with m symmetry, are present, forming sheets parallel to (100). The isolated EuF(8) dodeca-hedra exhibit a mean Eu-F distance of 2.356 Å. The K(+) cations are located within and between the sheets, leading to highly irregular KF(x) polyhedra (x = 8-9) around the alkali metal cations.