Y2Hf2O7 crystallizes in the monoclinic C2/m space group. Y(1) is bonded to two equivalent O(2) and four equivalent O(1) atoms to form distorted YO6 pentagonal pyramids that share corners with four equivalent Hf(1)O5 trigonal bipyramids, edges with three equivalent Y(1)O6 pentagonal pyramids, and edges with two equivalent Hf(1)O5 trigonal bipyramids. Hf(1) is bonded to one O(3), two equivalent O(1), and two equivalent O(2) atoms to form distorted HfO5 trigonal bipyramids that share corners with four equivalent Y(1)O6 pentagonal pyramids,  a cornercorner with one Hf(1)O5 trigonal bipyramid, edges with two equivalent Y(1)O6 pentagonal pyramids, and  an edgeedge with one Hf(1)O5 trigonal bipyramid. There are three inequivalent O sites. In the first O site, O(1) is bonded in a distorted trigonal non-coplanar geometry to two equivalent Y(1) and one Hf(1) atom. In the second O site, O(2) is bonded to two equivalent Y(1) and two equivalent Hf(1) atoms to form distorted edge-sharing OY2Hf2 trigonal pyramids. In the third O site, O(3) is bonded in a linear geometry to two equivalent Hf(1) atoms.
Y2Hf2O7 crystallizes in the monoclinic C2/m space group. Y(1) is bonded to two equivalent O(2) and four equivalent O(1) atoms to form distorted YO6 pentagonal pyramids that share corners with four equivalent Hf(1)O5 trigonal bipyramids, edges with three equivalent Y(1)O6 pentagonal pyramids, and edges with two equivalent Hf(1)O5 trigonal bipyramids. Both Y(1)-O(2) bond lengths are 2.37 Å. There are two shorter (2.22 Å) and two longer (2.33 Å) Y(1)-O(1) bond lengths. Hf(1) is bonded to one O(3), two equivalent O(1), and two equivalent O(2) atoms to form distorted HfO5 trigonal bipyramids that share corners with four equivalent Y(1)O6 pentagonal pyramids,  a cornercorner with one Hf(1)O5 trigonal bipyramid, edges with two equivalent Y(1)O6 pentagonal pyramids, and  an edgeedge with one Hf(1)O5 trigonal bipyramid. The Hf(1)-O(3) bond length is 1.95 Å. Both Hf(1)-O(1) bond lengths are 1.97 Å. There is one shorter (2.04 Å) and one longer (2.32 Å) Hf(1)-O(2) bond length. There are three inequivalent O sites. In the first O site, O(1) is bonded in a distorted trigonal non-coplanar geometry to two equivalent Y(1) and one Hf(1) atom. In the second O site, O(2) is bonded to two equivalent Y(1) and two equivalent Hf(1) atoms to form distorted edge-sharing OY2Hf2 trigonal pyramids. In the third O site, O(3) is bonded in a linear geometry to two equivalent Hf(1) atoms.