Ca4HfN4 crystallizes in the triclinic P-1 space group. There are four inequivalent Ca sites. In the first Ca site, Ca(1) is bonded in a distorted rectangular see-saw-like geometry to one N(1), one N(2), one N(3), and one N(4) atom. In the second Ca site, Ca(2) is bonded to two equivalent N(2) and two equivalent N(3) atoms to form distorted CaN4 tetrahedra that share corners with two equivalent Ca(3)N5 square pyramids, corners with two equivalent Ca(4)N5 square pyramids, corners with four equivalent Hf(1)N4 tetrahedra, and edges with two equivalent Ca(2)N4 tetrahedra. In the third Ca site, Ca(3) is bonded to one N(3), two equivalent N(1), and two equivalent N(4) atoms to form CaN5 square pyramids that share corners with three equivalent Ca(4)N5 square pyramids, corners with two equivalent Ca(2)N4 tetrahedra, corners with three equivalent Hf(1)N4 tetrahedra, edges with two equivalent Ca(3)N5 square pyramids, edges with three equivalent Ca(4)N5 square pyramids, and  an edgeedge with one Hf(1)N4 tetrahedra. In the fourth Ca site, Ca(4) is bonded to one N(3), two equivalent N(1), and two equivalent N(4) atoms to form CaN5 square pyramids that share corners with three equivalent Ca(3)N5 square pyramids,  a cornercorner with one Hf(1)N4 tetrahedra, corners with two equivalent Ca(2)N4 tetrahedra, edges with two equivalent Ca(4)N5 square pyramids, edges with three equivalent Ca(3)N5 square pyramids, and edges with two equivalent Hf(1)N4 tetrahedra. Hf(1) is bonded to one N(1), one N(2), one N(3), and one N(4) atom to form HfN4 tetrahedra that share  a cornercorner with one Ca(4)N5 square pyramid, corners with three equivalent Ca(3)N5 square pyramids, corners with four equivalent Ca(2)N4 tetrahedra,  an edgeedge with one Ca(3)N5 square pyramid, and edges with two equivalent Ca(4)N5 square pyramids. There are four inequivalent N sites. In the first N site, N(1) is bonded to one Ca(1), two equivalent Ca(3), two equivalent Ca(4), and one Hf(1) atom to form NCa5Hf octahedra that share corners with two equivalent N(3)Ca5Hf octahedra, corners with two equivalent N(4)Ca5Hf octahedra, corners with two equivalent N(2)Ca3Hf tetrahedra, edges with two equivalent N(1)Ca5Hf octahedra, edges with two equivalent N(3)Ca5Hf octahedra, and edges with four equivalent N(4)Ca5Hf octahedra. The corner-sharing octahedral tilt angles range from 8-19°. In the second N site, N(2) is bonded to one Ca(1), two equivalent Ca(2), and one Hf(1) atom to form distorted NCa3Hf tetrahedra that share corners with two equivalent N(1)Ca5Hf octahedra, corners with two equivalent N(4)Ca5Hf octahedra, corners with six equivalent N(3)Ca5Hf octahedra, and  an edgeedge with one N(2)Ca3Hf tetrahedra. The corner-sharing octahedral tilt angles range from 54-69°. In the third N site, N(3) is bonded to one Ca(1), one Ca(3), one Ca(4), two equivalent Ca(2), and one Hf(1) atom to form NCa5Hf octahedra that share corners with two equivalent N(1)Ca5Hf octahedra, corners with six equivalent N(2)Ca3Hf tetrahedra,  an edgeedge with one N(3)Ca5Hf octahedra, edges with two equivalent N(1)Ca5Hf octahedra, and edges with three equivalent N(4)Ca5Hf octahedra. The corner-sharing octahedral tilt angles range from 8-10°. In the fourth N site, N(4) is bonded to one Ca(1), two equivalent Ca(3), two equivalent Ca(4), and one Hf(1) atom to form NCa5Hf octahedra that share corners with two equivalent N(1)Ca5Hf octahedra, corners with two equivalent N(2)Ca3Hf tetrahedra, edges with two equivalent N(4)Ca5Hf octahedra, edges with three equivalent N(3)Ca5Hf octahedra, and edges with four equivalent N(1)Ca5Hf octahedra. The corner-sharing octahedral tilt angles range from 9-19°.
Ca4HfN4 crystallizes in the triclinic P-1 space group. There are four inequivalent Ca sites. In the first Ca site, Ca(1) is bonded in a distorted rectangular see-saw-like geometry to one N(1), one N(2), one N(3), and one N(4) atom. The Ca(1)-N(1) bond length is 2.47 Å. The Ca(1)-N(2) bond length is 2.39 Å. The Ca(1)-N(3) bond length is 2.44 Å. The Ca(1)-N(4) bond length is 2.45 Å. In the second Ca site, Ca(2) is bonded to two equivalent N(2) and two equivalent N(3) atoms to form distorted CaN4 tetrahedra that share corners with two equivalent Ca(3)N5 square pyramids, corners with two equivalent Ca(4)N5 square pyramids, corners with four equivalent Hf(1)N4 tetrahedra, and edges with two equivalent Ca(2)N4 tetrahedra. Both Ca(2)-N(2) bond lengths are 2.38 Å. There is one shorter (2.47 Å) and one longer (2.51 Å) Ca(2)-N(3) bond length. In the third Ca site, Ca(3) is bonded to one N(3), two equivalent N(1), and two equivalent N(4) atoms to form CaN5 square pyramids that share corners with three equivalent Ca(4)N5 square pyramids, corners with two equivalent Ca(2)N4 tetrahedra, corners with three equivalent Hf(1)N4 tetrahedra, edges with two equivalent Ca(3)N5 square pyramids, edges with three equivalent Ca(4)N5 square pyramids, and  an edgeedge with one Hf(1)N4 tetrahedra. The Ca(3)-N(3) bond length is 2.57 Å. There is one shorter (2.48 Å) and one longer (2.52 Å) Ca(3)-N(1) bond length. There is one shorter (2.46 Å) and one longer (2.52 Å) Ca(3)-N(4) bond length. In the fourth Ca site, Ca(4) is bonded to one N(3), two equivalent N(1), and two equivalent N(4) atoms to form CaN5 square pyramids that share corners with three equivalent Ca(3)N5 square pyramids,  a cornercorner with one Hf(1)N4 tetrahedra, corners with two equivalent Ca(2)N4 tetrahedra, edges with two equivalent Ca(4)N5 square pyramids, edges with three equivalent Ca(3)N5 square pyramids, and edges with two equivalent Hf(1)N4 tetrahedra. The Ca(4)-N(3) bond length is 2.50 Å. There is one shorter (2.52 Å) and one longer (2.53 Å) Ca(4)-N(1) bond length. There is one shorter (2.48 Å) and one longer (2.62 Å) Ca(4)-N(4) bond length. Hf(1) is bonded to one N(1), one N(2), one N(3), and one N(4) atom to form HfN4 tetrahedra that share  a cornercorner with one Ca(4)N5 square pyramid, corners with three equivalent Ca(3)N5 square pyramids, corners with four equivalent Ca(2)N4 tetrahedra,  an edgeedge with one Ca(3)N5 square pyramid, and edges with two equivalent Ca(4)N5 square pyramids. The Hf(1)-N(1) bond length is 2.08 Å. The Hf(1)-N(2) bond length is 2.04 Å. The Hf(1)-N(3) bond length is 2.07 Å. The Hf(1)-N(4) bond length is 2.08 Å. There are four inequivalent N sites. In the first N site, N(1) is bonded to one Ca(1), two equivalent Ca(3), two equivalent Ca(4), and one Hf(1) atom to form NCa5Hf octahedra that share corners with two equivalent N(3)Ca5Hf octahedra, corners with two equivalent N(4)Ca5Hf octahedra, corners with two equivalent N(2)Ca3Hf tetrahedra, edges with two equivalent N(1)Ca5Hf octahedra, edges with two equivalent N(3)Ca5Hf octahedra, and edges with four equivalent N(4)Ca5Hf octahedra. The corner-sharing octahedral tilt angles range from 8-19°. In the second N site, N(2) is bonded to one Ca(1), two equivalent Ca(2), and one Hf(1) atom to form distorted NCa3Hf tetrahedra that share corners with two equivalent N(1)Ca5Hf octahedra, corners with two equivalent N(4)Ca5Hf octahedra, corners with six equivalent N(3)Ca5Hf octahedra, and  an edgeedge with one N(2)Ca3Hf tetrahedra. The corner-sharing octahedral tilt angles range from 54-69°. In the third N site, N(3) is bonded to one Ca(1), one Ca(3), one Ca(4), two equivalent Ca(2), and one Hf(1) atom to form NCa5Hf octahedra that share corners with two equivalent N(1)Ca5Hf octahedra, corners with six equivalent N(2)Ca3Hf tetrahedra,  an edgeedge with one N(3)Ca5Hf octahedra, edges with two equivalent N(1)Ca5Hf octahedra, and edges with three equivalent N(4)Ca5Hf octahedra. The corner-sharing octahedral tilt angles range from 8-10°. In the fourth N site, N(4) is bonded to one Ca(1), two equivalent Ca(3), two equivalent Ca(4), and one Hf(1) atom to form NCa5Hf octahedra that share corners with two equivalent N(1)Ca5Hf octahedra, corners with two equivalent N(2)Ca3Hf tetrahedra, edges with two equivalent N(4)Ca5Hf octahedra, edges with three equivalent N(3)Ca5Hf octahedra, and edges with four equivalent N(1)Ca5Hf octahedra. The corner-sharing octahedral tilt angles range from 9-19°.