Hf6PbO18 crystallizes in the monoclinic C2/m space group. There are two inequivalent Hf sites. In the first Hf site, Hf(1) is bonded to one O(1), one O(2), one O(3), one O(5), one O(6), and one O(7) atom to form HfO6 octahedra that share corners with two equivalent Hf(2)O6 octahedra, corners with four equivalent Hf(1)O6 octahedra, and  a faceface with one Pb(1)O12 cuboctahedra. The corner-sharing octahedral tilt angles range from 0-10°. In the second Hf site, Hf(2) is bonded to two equivalent O(2), two equivalent O(4), and two equivalent O(7) atoms to form HfO6 octahedra that share corners with two equivalent Hf(2)O6 octahedra, corners with four equivalent Hf(1)O6 octahedra, and faces with two equivalent Pb(1)O12 cuboctahedra. The corner-sharing octahedral tilt angles range from 6-8°. Pb(1) is bonded to two equivalent O(3), two equivalent O(4), four equivalent O(2), and four equivalent O(7) atoms to form PbO12 cuboctahedra that share faces with four equivalent Hf(1)O6 octahedra and faces with four equivalent Hf(2)O6 octahedra. There are seven inequivalent O sites. In the first O site, O(1) is bonded in a linear geometry to two equivalent Hf(1) atoms. In the second O site, O(2) is bonded in a linear geometry to one Hf(1), one Hf(2), and one Pb(1) atom. In the third O site, O(3) is bonded in a distorted linear geometry to two equivalent Hf(1) and one Pb(1) atom. In the fourth O site, O(4) is bonded in a linear geometry to two equivalent Hf(2) and one Pb(1) atom. In the fifth O site, O(5) is bonded in a linear geometry to two equivalent Hf(1) atoms. In the sixth O site, O(6) is bonded in a linear geometry to two equivalent Hf(1) atoms. In the seventh O site, O(7) is bonded in a linear geometry to one Hf(1), one Hf(2), and one Pb(1) atom.
Hf6PbO18 crystallizes in the monoclinic C2/m space group. There are two inequivalent Hf sites. In the first Hf site, Hf(1) is bonded to one O(1), one O(2), one O(3), one O(5), one O(6), and one O(7) atom to form HfO6 octahedra that share corners with two equivalent Hf(2)O6 octahedra, corners with four equivalent Hf(1)O6 octahedra, and  a faceface with one Pb(1)O12 cuboctahedra. The corner-sharing octahedral tilt angles range from 0-10°. The Hf(1)-O(1) bond length is 2.04 Å. The Hf(1)-O(2) bond length is 2.10 Å. The Hf(1)-O(3) bond length is 2.11 Å. The Hf(1)-O(5) bond length is 2.04 Å. The Hf(1)-O(6) bond length is 2.04 Å. The Hf(1)-O(7) bond length is 2.10 Å. In the second Hf site, Hf(2) is bonded to two equivalent O(2), two equivalent O(4), and two equivalent O(7) atoms to form HfO6 octahedra that share corners with two equivalent Hf(2)O6 octahedra, corners with four equivalent Hf(1)O6 octahedra, and faces with two equivalent Pb(1)O12 cuboctahedra. The corner-sharing octahedral tilt angles range from 6-8°. Both Hf(2)-O(2) bond lengths are 2.08 Å. Both Hf(2)-O(4) bond lengths are 2.07 Å. Both Hf(2)-O(7) bond lengths are 2.08 Å. Pb(1) is bonded to two equivalent O(3), two equivalent O(4), four equivalent O(2), and four equivalent O(7) atoms to form PbO12 cuboctahedra that share faces with four equivalent Hf(1)O6 octahedra and faces with four equivalent Hf(2)O6 octahedra. Both Pb(1)-O(3) bond lengths are 2.78 Å. Both Pb(1)-O(4) bond lengths are 2.83 Å. All Pb(1)-O(2) bond lengths are 2.80 Å. All Pb(1)-O(7) bond lengths are 2.80 Å. There are seven inequivalent O sites. In the first O site, O(1) is bonded in a linear geometry to two equivalent Hf(1) atoms. In the second O site, O(2) is bonded in a linear geometry to one Hf(1), one Hf(2), and one Pb(1) atom. In the third O site, O(3) is bonded in a distorted linear geometry to two equivalent Hf(1) and one Pb(1) atom. In the fourth O site, O(4) is bonded in a linear geometry to two equivalent Hf(2) and one Pb(1) atom. In the fifth O site, O(5) is bonded in a linear geometry to two equivalent Hf(1) atoms. In the sixth O site, O(6) is bonded in a linear geometry to two equivalent Hf(1) atoms. In the seventh O site, O(7) is bonded in a linear geometry to one Hf(1), one Hf(2), and one Pb(1) atom.