HfH4(C2O)4 crystallizes in the tetragonal I4/mmm space group. There are two inequivalent Hf sites. In the first Hf site, Hf(1) is bonded in a 8-coordinate geometry to four equivalent O(1) and four equivalent O(3) atoms. All Hf(1)-O(1) bond lengths are 2.18 Å. All Hf(1)-O(3) bond lengths are 2.17 Å. In the second Hf site, Hf(2) is bonded in a 6-coordinate geometry to two equivalent O(2) and four equivalent O(3) atoms. Both Hf(2)-O(2) bond lengths are 2.23 Å. All Hf(2)-O(3) bond lengths are 2.12 Å. There are six inequivalent C sites. In the first C site, C(5) is bonded in a trigonal planar geometry to one C(4), one C(5), and one C(6) atom. The C(5)-C(4) bond length is 1.39 Å. The C(5)-C(5) bond length is 1.42 Å. The C(5)-C(6) bond length is 1.36 Å. In the second C site, C(6) is bonded in a distorted single-bond geometry to one C(2), one C(5), and one H(3) atom. The C(6)-C(2) bond length is 1.39 Å. The C(6)-H(3) bond length is 0.93 Å. In the third C site, C(1) is bonded in a distorted bent 120 degrees geometry to one C(2), one O(1), and one O(2) atom. The C(1)-C(2) bond length is 1.50 Å. The C(1)-O(1) bond length is 1.22 Å. The C(1)-O(2) bond length is 1.28 Å. In the fourth C site, C(2) is bonded in a trigonal planar geometry to one C(1), one C(3), and one C(6) atom. The C(2)-C(3) bond length is 1.38 Å. In the fifth C site, C(3) is bonded in a single-bond geometry to one C(2) and one H(1) atom. The C(3)-H(1) bond length is 0.93 Å. In the sixth C site, C(4) is bonded in a distorted single-bond geometry to one C(5) and one H(2) atom. The C(4)-H(2) bond length is 0.93 Å. There are three inequivalent H sites. In the first H site, H(1) is bonded in a single-bond geometry to one C(3) atom. In the second H site, H(2) is bonded in a single-bond geometry to one C(4) atom. In the third H site, H(3) is bonded in a single-bond geometry to one C(6) atom. There are three inequivalent O sites. In the first O site, O(3) is bonded in a trigonal non-coplanar geometry to one Hf(1) and two equivalent Hf(2) atoms. In the second O site, O(1) is bonded in a distorted bent 120 degrees geometry to one Hf(1) and one C(1) atom. In the third O site, O(2) is bonded in a 2-coordinate geometry to one Hf(2) and one C(1) atom. Linkers: 4 [O]C(=O)c1ccc2cc(C([O])=O)ccc2c1. Metal clusters: 1 O=[C]O[Hf]123(O[C]=O)O[Hf]456(O[C]O[Hf]O[C]O[Hf]7(O[C]O[Hf]O[C]O4)(O1)(O2)O[Hf](O[C]=O)(O[C]=O)(O5)(O6)O7)O3. RCSR code: bcu. The MOF has largest included sphere 10.67 A, density 0.98 g/cm3, surface area 2230.64 m2/g, accessible volume 0.80 cm3/g