CsEuTa6Cl18 crystallizes in the trigonal P-31c space group. Cs(1) is bonded in a 12-coordinate geometry to six equivalent Cl(1) and six equivalent Cl(2) atoms. Eu(1) is bonded to six equivalent Cl(1) atoms to form EuCl6 octahedra that share corners with six equivalent Ta(1)Cl5 square pyramids. Ta(1) is bonded to one Cl(1), two equivalent Cl(2), and two equivalent Cl(3) atoms to form distorted TaCl5 square pyramids that share  a cornercorner with one Eu(1)Cl6 octahedra and corners with four equivalent Ta(1)Cl5 square pyramids. The corner-sharing octahedral tilt angles are 46°. There are three inequivalent Cl sites. In the first Cl site, Cl(3) is bonded in a 2-coordinate geometry to two equivalent Ta(1) atoms. In the second Cl site, Cl(1) is bonded in a 3-coordinate geometry to one Cs(1), one Eu(1), and one Ta(1) atom. In the third Cl site, Cl(2) is bonded in a 2-coordinate geometry to one Cs(1) and two equivalent Ta(1) atoms.
CsEuTa6Cl18 crystallizes in the trigonal P-31c space group. Cs(1) is bonded in a 12-coordinate geometry to six equivalent Cl(1) and six equivalent Cl(2) atoms. All Cs(1)-Cl(1) bond lengths are 3.85 Å. All Cs(1)-Cl(2) bond lengths are 3.99 Å. Eu(1) is bonded to six equivalent Cl(1) atoms to form EuCl6 octahedra that share corners with six equivalent Ta(1)Cl5 square pyramids. All Eu(1)-Cl(1) bond lengths are 2.88 Å. Ta(1) is bonded to one Cl(1), two equivalent Cl(2), and two equivalent Cl(3) atoms to form distorted TaCl5 square pyramids that share  a cornercorner with one Eu(1)Cl6 octahedra and corners with four equivalent Ta(1)Cl5 square pyramids. The corner-sharing octahedral tilt angles are 46°. The Ta(1)-Cl(1) bond length is 2.62 Å. There is one shorter (2.45 Å) and one longer (2.46 Å) Ta(1)-Cl(2) bond length. Both Ta(1)-Cl(3) bond lengths are 2.45 Å. There are three inequivalent Cl sites. In the first Cl site, Cl(3) is bonded in a 2-coordinate geometry to two equivalent Ta(1) atoms. In the second Cl site, Cl(1) is bonded in a 3-coordinate geometry to one Cs(1), one Eu(1), and one Ta(1) atom. In the third Cl site, Cl(2) is bonded in a 2-coordinate geometry to one Cs(1) and two equivalent Ta(1) atoms.