An Ordered Assembly of Filled Nanoscale Tubules of Europium Seleno-silicate in the Crystal Structure of a Quaternary Compound

A quaternary compound of the composition Na2EuSiSe4 featuring filled nanotubules was isolated from a reaction of elemental Eu, Si, and Se in Na2Se2 flux. The compound crystallizes in the trigonal system, space group = R3c, a = 24.397(1), c = 7.1468(9) Å, V = 3684.2(6) Å3. The structure is composed of quasi-infinite nanoscale tubules of [EuSiSe4]2-n, filled with Na+ cations and held together by Na+ cations through ionic interactions. The tubules are constructed through a complex network of monocapped EuSe7 trigonal prisms and SiSe4 tetrahedra. Three EuSe7 polyhedra are corner-shared to form isosceles triangular clusters that are stacked one over the other in a staggered fashion and fused together through edge-sharing to form a tubule surrounded by SiSe4 tetrahedra. The inner and outer crystallographic diameters of the tubules are 4.05(2) and 12.14(1) Å, respectively.