NpNi5 crystallizes in the orthorhombic Cmmm space group. Np(1) is bonded in a 18-coordinate geometry to four equivalent Ni(2), six equivalent Ni(3), and eight equivalent Ni(1) atoms. There are three inequivalent Ni sites. In the first Ni site, Ni(1) is bonded to four equivalent Np(1), two equivalent Ni(1), two equivalent Ni(2), and four equivalent Ni(3) atoms to form NiNp4Ni8 cuboctahedra that share corners with four equivalent Ni(2)Np4Ni8 cuboctahedra, corners with eight equivalent Ni(3)Np3Ni6 cuboctahedra, corners with twelve equivalent Ni(1)Np4Ni8 cuboctahedra, edges with four equivalent Ni(2)Np4Ni8 cuboctahedra, edges with six equivalent Ni(1)Np4Ni8 cuboctahedra, edges with eight equivalent Ni(3)Np3Ni6 cuboctahedra, faces with four equivalent Ni(3)Np3Ni6 cuboctahedra, faces with four equivalent Ni(2)Np4Ni8 cuboctahedra, and faces with six equivalent Ni(1)Np4Ni8 cuboctahedra. In the second Ni site, Ni(2) is bonded to four equivalent Np(1), four equivalent Ni(1), and four equivalent Ni(3) atoms to form NiNp4Ni8 cuboctahedra that share corners with eight equivalent Ni(3)Np3Ni6 cuboctahedra, corners with eight equivalent Ni(1)Np4Ni8 cuboctahedra, corners with eight equivalent Ni(2)Np4Ni8 cuboctahedra, edges with two equivalent Ni(2)Np4Ni8 cuboctahedra, edges with eight equivalent Ni(3)Np3Ni6 cuboctahedra, edges with eight equivalent Ni(1)Np4Ni8 cuboctahedra, faces with two equivalent Ni(2)Np4Ni8 cuboctahedra, faces with four equivalent Ni(3)Np3Ni6 cuboctahedra, and faces with eight equivalent Ni(1)Np4Ni8 cuboctahedra. In the third Ni site, Ni(3) is bonded to three equivalent Np(1), two equivalent Ni(2), and four equivalent Ni(1) atoms to form distorted NiNp3Ni6 cuboctahedra that share corners with four equivalent Ni(2)Np4Ni8 cuboctahedra, corners with eight equivalent Ni(1)Np4Ni8 cuboctahedra, corners with fifteen equivalent Ni(3)Np3Ni6 cuboctahedra, edges with four equivalent Ni(2)Np4Ni8 cuboctahedra, edges with eight equivalent Ni(1)Np4Ni8 cuboctahedra, faces with two equivalent Ni(2)Np4Ni8 cuboctahedra, faces with four equivalent Ni(1)Np4Ni8 cuboctahedra, and faces with five equivalent Ni(3)Np3Ni6 cuboctahedra.
NpNi5 crystallizes in the orthorhombic Cmmm space group. Np(1) is bonded in a 18-coordinate geometry to four equivalent Ni(2), six equivalent Ni(3), and eight equivalent Ni(1) atoms. All Np(1)-Ni(2) bond lengths are 3.12 Å. There are two shorter (2.79 Å) and four longer (2.80 Å) Np(1)-Ni(3) bond lengths. All Np(1)-Ni(1) bond lengths are 3.12 Å. There are three inequivalent Ni sites. In the first Ni site, Ni(1) is bonded to four equivalent Np(1), two equivalent Ni(1), two equivalent Ni(2), and four equivalent Ni(3) atoms to form NiNp4Ni8 cuboctahedra that share corners with four equivalent Ni(2)Np4Ni8 cuboctahedra, corners with eight equivalent Ni(3)Np3Ni6 cuboctahedra, corners with twelve equivalent Ni(1)Np4Ni8 cuboctahedra, edges with four equivalent Ni(2)Np4Ni8 cuboctahedra, edges with six equivalent Ni(1)Np4Ni8 cuboctahedra, edges with eight equivalent Ni(3)Np3Ni6 cuboctahedra, faces with four equivalent Ni(3)Np3Ni6 cuboctahedra, faces with four equivalent Ni(2)Np4Ni8 cuboctahedra, and faces with six equivalent Ni(1)Np4Ni8 cuboctahedra. Both Ni(1)-Ni(1) bond lengths are 2.43 Å. Both Ni(1)-Ni(2) bond lengths are 2.42 Å. All Ni(1)-Ni(3) bond lengths are 2.41 Å. In the second Ni site, Ni(2) is bonded to four equivalent Np(1), four equivalent Ni(1), and four equivalent Ni(3) atoms to form NiNp4Ni8 cuboctahedra that share corners with eight equivalent Ni(3)Np3Ni6 cuboctahedra, corners with eight equivalent Ni(1)Np4Ni8 cuboctahedra, corners with eight equivalent Ni(2)Np4Ni8 cuboctahedra, edges with two equivalent Ni(2)Np4Ni8 cuboctahedra, edges with eight equivalent Ni(3)Np3Ni6 cuboctahedra, edges with eight equivalent Ni(1)Np4Ni8 cuboctahedra, faces with two equivalent Ni(2)Np4Ni8 cuboctahedra, faces with four equivalent Ni(3)Np3Ni6 cuboctahedra, and faces with eight equivalent Ni(1)Np4Ni8 cuboctahedra. All Ni(2)-Ni(3) bond lengths are 2.41 Å. In the third Ni site, Ni(3) is bonded to three equivalent Np(1), two equivalent Ni(2), and four equivalent Ni(1) atoms to form distorted NiNp3Ni6 cuboctahedra that share corners with four equivalent Ni(2)Np4Ni8 cuboctahedra, corners with eight equivalent Ni(1)Np4Ni8 cuboctahedra, corners with fifteen equivalent Ni(3)Np3Ni6 cuboctahedra, edges with four equivalent Ni(2)Np4Ni8 cuboctahedra, edges with eight equivalent Ni(1)Np4Ni8 cuboctahedra, faces with two equivalent Ni(2)Np4Ni8 cuboctahedra, faces with four equivalent Ni(1)Np4Ni8 cuboctahedra, and faces with five equivalent Ni(3)Np3Ni6 cuboctahedra.