HfNb4CN4 is alpha Po-derived structured and crystallizes in the tetragonal I4/mmm space group. Hf(1) is bonded to four equivalent C(1) and two equivalent N(1) atoms to form HfC4N2 octahedra that share corners with two equivalent Nb(2)N6 octahedra, corners with four equivalent Hf(1)C4N2 octahedra, edges with four equivalent Hf(1)C4N2 octahedra, and edges with eight equivalent Nb(1)CN5 octahedra. The corner-sharing octahedra are not tilted. There are two inequivalent Nb sites. In the first Nb site, Nb(1) is bonded to one C(1), one N(2), and four equivalent N(1) atoms to form NbCN5 octahedra that share  a cornercorner with one Nb(2)N6 octahedra, corners with five equivalent Nb(1)CN5 octahedra, edges with four equivalent Hf(1)C4N2 octahedra, edges with four equivalent Nb(1)CN5 octahedra, and edges with four equivalent Nb(2)N6 octahedra. The corner-sharing octahedral tilt angles range from 0-1°. In the second Nb site, Nb(2) is bonded to one N(1) and five equivalent N(2) atoms to form NbN6 octahedra that share  a cornercorner with one Hf(1)C4N2 octahedra,  a cornercorner with one Nb(1)CN5 octahedra, corners with four equivalent Nb(2)N6 octahedra, edges with four equivalent Nb(1)CN5 octahedra, and edges with eight equivalent Nb(2)N6 octahedra. The corner-sharing octahedra are not tilted. C(1) is bonded to four equivalent Hf(1) and two equivalent Nb(1) atoms to form CHf4Nb2 octahedra that share corners with two equivalent N(2)Nb6 octahedra, corners with four equivalent C(1)Hf4Nb2 octahedra, edges with four equivalent C(1)Hf4Nb2 octahedra, and edges with eight equivalent N(1)HfNb5 octahedra. The corner-sharing octahedra are not tilted. There are two inequivalent N sites. In the first N site, N(1) is bonded to one Hf(1), one Nb(2), and four equivalent Nb(1) atoms to form NHfNb5 octahedra that share  a cornercorner with one N(2)Nb6 octahedra, corners with five equivalent N(1)HfNb5 octahedra, edges with four equivalent C(1)Hf4Nb2 octahedra, edges with four equivalent N(1)HfNb5 octahedra, and edges with four equivalent N(2)Nb6 octahedra. The corner-sharing octahedral tilt angles range from 0-1°. In the second N site, N(2) is bonded to one Nb(1) and five equivalent Nb(2) atoms to form NNb6 octahedra that share  a cornercorner with one C(1)Hf4Nb2 octahedra,  a cornercorner with one N(1)HfNb5 octahedra, corners with four equivalent N(2)Nb6 octahedra, edges with four equivalent N(1)HfNb5 octahedra, and edges with eight equivalent N(2)Nb6 octahedra. The corner-sharing octahedra are not tilted.
HfNb4CN4 is alpha Po-derived structured and crystallizes in the tetragonal I4/mmm space group. Hf(1) is bonded to four equivalent C(1) and two equivalent N(1) atoms to form HfC4N2 octahedra that share corners with two equivalent Nb(2)N6 octahedra, corners with four equivalent Hf(1)C4N2 octahedra, edges with four equivalent Hf(1)C4N2 octahedra, and edges with eight equivalent Nb(1)CN5 octahedra. The corner-sharing octahedra are not tilted. All Hf(1)-C(1) bond lengths are 2.25 Å. Both Hf(1)-N(1) bond lengths are 2.24 Å. There are two inequivalent Nb sites. In the first Nb site, Nb(1) is bonded to one C(1), one N(2), and four equivalent N(1) atoms to form NbCN5 octahedra that share  a cornercorner with one Nb(2)N6 octahedra, corners with five equivalent Nb(1)CN5 octahedra, edges with four equivalent Hf(1)C4N2 octahedra, edges with four equivalent Nb(1)CN5 octahedra, and edges with four equivalent Nb(2)N6 octahedra. The corner-sharing octahedral tilt angles range from 0-1°. The Nb(1)-C(1) bond length is 2.22 Å. The Nb(1)-N(2) bond length is 2.25 Å. All Nb(1)-N(1) bond lengths are 2.25 Å. In the second Nb site, Nb(2) is bonded to one N(1) and five equivalent N(2) atoms to form NbN6 octahedra that share  a cornercorner with one Hf(1)C4N2 octahedra,  a cornercorner with one Nb(1)CN5 octahedra, corners with four equivalent Nb(2)N6 octahedra, edges with four equivalent Nb(1)CN5 octahedra, and edges with eight equivalent Nb(2)N6 octahedra. The corner-sharing octahedra are not tilted. The Nb(2)-N(1) bond length is 2.23 Å. There is one shorter (2.21 Å) and four longer (2.25 Å) Nb(2)-N(2) bond lengths. C(1) is bonded to four equivalent Hf(1) and two equivalent Nb(1) atoms to form CHf4Nb2 octahedra that share corners with two equivalent N(2)Nb6 octahedra, corners with four equivalent C(1)Hf4Nb2 octahedra, edges with four equivalent C(1)Hf4Nb2 octahedra, and edges with eight equivalent N(1)HfNb5 octahedra. The corner-sharing octahedra are not tilted. There are two inequivalent N sites. In the first N site, N(1) is bonded to one Hf(1), one Nb(2), and four equivalent Nb(1) atoms to form NHfNb5 octahedra that share  a cornercorner with one N(2)Nb6 octahedra, corners with five equivalent N(1)HfNb5 octahedra, edges with four equivalent C(1)Hf4Nb2 octahedra, edges with four equivalent N(1)HfNb5 octahedra, and edges with four equivalent N(2)Nb6 octahedra. The corner-sharing octahedral tilt angles range from 0-1°. In the second N site, N(2) is bonded to one Nb(1) and five equivalent Nb(2) atoms to form NNb6 octahedra that share  a cornercorner with one C(1)Hf4Nb2 octahedra,  a cornercorner with one N(1)HfNb5 octahedra, corners with four equivalent N(2)Nb6 octahedra, edges with four equivalent N(1)HfNb5 octahedra, and edges with eight equivalent N(2)Nb6 octahedra. The corner-sharing octahedra are not tilted.