Rb2CaNd2(WO4)4 crystallizes in the monoclinic C2 space group. There are two inequivalent Rb sites. In the first Rb site, Rb(1) is bonded in a 11-coordinate geometry to one Ca(1), two equivalent O(2), two equivalent O(3), two equivalent O(4), two equivalent O(7), and two equivalent O(8) atoms. In the second Rb site, Rb(2) is bonded in a 10-coordinate geometry to two equivalent O(2), two equivalent O(4), two equivalent O(5), two equivalent O(6), and two equivalent O(8) atoms. Ca(1) is bonded in a 4-coordinate geometry to one Rb(1), two equivalent O(1), and two equivalent O(5) atoms. There are two inequivalent Nd sites. In the first Nd site, Nd(1) is bonded to two equivalent O(2), two equivalent O(4), and two equivalent O(6) atoms to form distorted NdO6 pentagonal pyramids that share corners with four equivalent W(1)O6 octahedra and corners with four equivalent W(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 21-58°. In the second Nd site, Nd(2) is bonded to two equivalent O(1), two equivalent O(3), and two equivalent O(7) atoms to form distorted NdO6 pentagonal pyramids that share corners with four equivalent W(1)O6 octahedra and corners with four equivalent W(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 27-58°. There are two inequivalent W sites. In the first W site, W(1) is bonded to one O(1), one O(2), one O(3), one O(5), one O(6), and one O(8) atom to form WO6 octahedra that share corners with two equivalent W(2)O6 octahedra, corners with two equivalent Nd(1)O6 pentagonal pyramids, corners with two equivalent Nd(2)O6 pentagonal pyramids, and  an edgeedge with one W(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 35-36°. In the second W site, W(2) is bonded to one O(1), one O(4), one O(5), one O(6), one O(7), and one O(8) atom to form WO6 octahedra that share corners with two equivalent W(1)O6 octahedra, corners with two equivalent Nd(1)O6 pentagonal pyramids, corners with two equivalent Nd(2)O6 pentagonal pyramids, and  an edgeedge with one W(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 35-36°. There are eight inequivalent O sites. In the first O site, O(1) is bonded to one Ca(1), one Nd(2), one W(1), and one W(2) atom to form distorted corner-sharing OCaNdW2 trigonal pyramids. In the second O site, O(2) is bonded in a 4-coordinate geometry to one Rb(1), one Rb(2), one Nd(1), and one W(1) atom. In the third O site, O(3) is bonded in a 3-coordinate geometry to one Rb(1), one Nd(2), and one W(1) atom. In the fourth O site, O(4) is bonded in a 4-coordinate geometry to one Rb(1), one Rb(2), one Nd(1), and one W(2) atom. In the fifth O site, O(5) is bonded in a 3-coordinate geometry to one Rb(2), one Ca(1), one W(1), and one W(2) atom. In the sixth O site, O(6) is bonded in a 4-coordinate geometry to one Rb(2), one Nd(1), one W(1), and one W(2) atom. In the seventh O site, O(7) is bonded in a 3-coordinate geometry to one Rb(1), one Nd(2), and one W(2) atom. In the eighth O site, O(8) is bonded in a 4-coordinate geometry to one Rb(1), one Rb(2), one W(1), and one W(2) atom.
Rb2CaNd2(WO4)4 crystallizes in the monoclinic C2 space group. There are two inequivalent Rb sites. In the first Rb site, Rb(1) is bonded in a 11-coordinate geometry to one Ca(1), two equivalent O(2), two equivalent O(3), two equivalent O(4), two equivalent O(7), and two equivalent O(8) atoms. The Rb(1)-Ca(1) bond length is 2.92 Å. Both Rb(1)-O(2) bond lengths are 2.88 Å. Both Rb(1)-O(3) bond lengths are 2.92 Å. Both Rb(1)-O(4) bond lengths are 2.92 Å. Both Rb(1)-O(7) bond lengths are 2.87 Å. Both Rb(1)-O(8) bond lengths are 2.80 Å. In the second Rb site, Rb(2) is bonded in a 10-coordinate geometry to two equivalent O(2), two equivalent O(4), two equivalent O(5), two equivalent O(6), and two equivalent O(8) atoms. Both Rb(2)-O(2) bond lengths are 3.04 Å. Both Rb(2)-O(4) bond lengths are 3.03 Å. Both Rb(2)-O(5) bond lengths are 3.22 Å. Both Rb(2)-O(6) bond lengths are 3.09 Å. Both Rb(2)-O(8) bond lengths are 3.07 Å. Ca(1) is bonded in a 4-coordinate geometry to one Rb(1), two equivalent O(1), and two equivalent O(5) atoms. Both Ca(1)-O(1) bond lengths are 2.31 Å. Both Ca(1)-O(5) bond lengths are 2.21 Å. There are two inequivalent Nd sites. In the first Nd site, Nd(1) is bonded to two equivalent O(2), two equivalent O(4), and two equivalent O(6) atoms to form distorted NdO6 pentagonal pyramids that share corners with four equivalent W(1)O6 octahedra and corners with four equivalent W(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 21-58°. Both Nd(1)-O(2) bond lengths are 2.43 Å. Both Nd(1)-O(4) bond lengths are 2.44 Å. Both Nd(1)-O(6) bond lengths are 2.38 Å. In the second Nd site, Nd(2) is bonded to two equivalent O(1), two equivalent O(3), and two equivalent O(7) atoms to form distorted NdO6 pentagonal pyramids that share corners with four equivalent W(1)O6 octahedra and corners with four equivalent W(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 27-58°. Both Nd(2)-O(1) bond lengths are 2.49 Å. Both Nd(2)-O(3) bond lengths are 2.36 Å. Both Nd(2)-O(7) bond lengths are 2.39 Å. There are two inequivalent W sites. In the first W site, W(1) is bonded to one O(1), one O(2), one O(3), one O(5), one O(6), and one O(8) atom to form WO6 octahedra that share corners with two equivalent W(2)O6 octahedra, corners with two equivalent Nd(1)O6 pentagonal pyramids, corners with two equivalent Nd(2)O6 pentagonal pyramids, and  an edgeedge with one W(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 35-36°. The W(1)-O(1) bond length is 2.19 Å. The W(1)-O(2) bond length is 1.87 Å. The W(1)-O(3) bond length is 1.92 Å. The W(1)-O(5) bond length is 2.07 Å. The W(1)-O(6) bond length is 2.10 Å. The W(1)-O(8) bond length is 2.06 Å. In the second W site, W(2) is bonded to one O(1), one O(4), one O(5), one O(6), one O(7), and one O(8) atom to form WO6 octahedra that share corners with two equivalent W(1)O6 octahedra, corners with two equivalent Nd(1)O6 pentagonal pyramids, corners with two equivalent Nd(2)O6 pentagonal pyramids, and  an edgeedge with one W(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 35-36°. The W(2)-O(1) bond length is 2.10 Å. The W(2)-O(4) bond length is 1.86 Å. The W(2)-O(5) bond length is 2.01 Å. The W(2)-O(6) bond length is 2.07 Å. The W(2)-O(7) bond length is 1.86 Å. The W(2)-O(8) bond length is 1.91 Å. There are eight inequivalent O sites. In the first O site, O(1) is bonded to one Ca(1), one Nd(2), one W(1), and one W(2) atom to form distorted corner-sharing OCaNdW2 trigonal pyramids. In the second O site, O(2) is bonded in a 4-coordinate geometry to one Rb(1), one Rb(2), one Nd(1), and one W(1) atom. In the third O site, O(3) is bonded in a 3-coordinate geometry to one Rb(1), one Nd(2), and one W(1) atom. In the fourth O site, O(4) is bonded in a 4-coordinate geometry to one Rb(1), one Rb(2), one Nd(1), and one W(2) atom. In the fifth O site, O(5) is bonded in a 3-coordinate geometry to one Rb(2), one Ca(1), one W(1), and one W(2) atom. In the sixth O site, O(6) is bonded in a 4-coordinate geometry to one Rb(2), one Nd(1), one W(1), and one W(2) atom. In the seventh O site, O(7) is bonded in a 3-coordinate geometry to one Rb(1), one Nd(2), and one W(2) atom. In the eighth O site, O(8) is bonded in a 4-coordinate geometry to one Rb(1), one Rb(2), one W(1), and one W(2) atom.