YNi4Si is Frank-Kasper $\mu$ Phase-derived structured and crystallizes in the orthorhombic Cmmm space group. Y(1) is bonded in a 18-coordinate geometry to six equivalent Ni(1), eight equivalent Ni(2), and four equivalent Si(1) atoms. There are two inequivalent Ni sites. In the first Ni site, Ni(1) is bonded in a 12-coordinate geometry to three equivalent Y(1), three equivalent Ni(1), four equivalent Ni(2), and two equivalent Si(1) atoms. In the second Ni site, Ni(2) is bonded to four equivalent Y(1), two equivalent Ni(2), four equivalent Ni(1), and two equivalent Si(1) atoms to form NiY4Si2Ni6 cuboctahedra that share corners with four equivalent Si(1)Y4Ni8 cuboctahedra, corners with twelve equivalent Ni(2)Y4Si2Ni6 cuboctahedra, edges with four equivalent Si(1)Y4Ni8 cuboctahedra, edges with six equivalent Ni(2)Y4Si2Ni6 cuboctahedra, faces with four equivalent Si(1)Y4Ni8 cuboctahedra, and faces with six equivalent Ni(2)Y4Si2Ni6 cuboctahedra. Si(1) is bonded to four equivalent Y(1), four equivalent Ni(1), and four equivalent Ni(2) atoms to form distorted SiY4Ni8 cuboctahedra that share corners with eight equivalent Ni(2)Y4Si2Ni6 cuboctahedra, corners with eight equivalent Si(1)Y4Ni8 cuboctahedra, edges with two equivalent Si(1)Y4Ni8 cuboctahedra, edges with eight equivalent Ni(2)Y4Si2Ni6 cuboctahedra, faces with two equivalent Si(1)Y4Ni8 cuboctahedra, and faces with eight equivalent Ni(2)Y4Si2Ni6 cuboctahedra.
YNi4Si is Frank-Kasper $\mu$ Phase-derived structured and crystallizes in the orthorhombic Cmmm space group. Y(1) is bonded in a 18-coordinate geometry to six equivalent Ni(1), eight equivalent Ni(2), and four equivalent Si(1) atoms. There are two shorter (2.77 Å) and four longer (2.82 Å) Y(1)-Ni(1) bond lengths. All Y(1)-Ni(2) bond lengths are 3.09 Å. All Y(1)-Si(1) bond lengths are 3.18 Å. There are two inequivalent Ni sites. In the first Ni site, Ni(1) is bonded in a 12-coordinate geometry to three equivalent Y(1), three equivalent Ni(1), four equivalent Ni(2), and two equivalent Si(1) atoms. There is one shorter (2.58 Å) and two longer (2.92 Å) Ni(1)-Ni(1) bond lengths. All Ni(1)-Ni(2) bond lengths are 2.44 Å. Both Ni(1)-Si(1) bond lengths are 2.34 Å. In the second Ni site, Ni(2) is bonded to four equivalent Y(1), two equivalent Ni(2), four equivalent Ni(1), and two equivalent Si(1) atoms to form NiY4Si2Ni6 cuboctahedra that share corners with four equivalent Si(1)Y4Ni8 cuboctahedra, corners with twelve equivalent Ni(2)Y4Si2Ni6 cuboctahedra, edges with four equivalent Si(1)Y4Ni8 cuboctahedra, edges with six equivalent Ni(2)Y4Si2Ni6 cuboctahedra, faces with four equivalent Si(1)Y4Ni8 cuboctahedra, and faces with six equivalent Ni(2)Y4Si2Ni6 cuboctahedra. Both Ni(2)-Ni(2) bond lengths are 2.51 Å. Both Ni(2)-Si(1) bond lengths are 2.39 Å. Si(1) is bonded to four equivalent Y(1), four equivalent Ni(1), and four equivalent Ni(2) atoms to form distorted SiY4Ni8 cuboctahedra that share corners with eight equivalent Ni(2)Y4Si2Ni6 cuboctahedra, corners with eight equivalent Si(1)Y4Ni8 cuboctahedra, edges with two equivalent Si(1)Y4Ni8 cuboctahedra, edges with eight equivalent Ni(2)Y4Si2Ni6 cuboctahedra, faces with two equivalent Si(1)Y4Ni8 cuboctahedra, and faces with eight equivalent Ni(2)Y4Si2Ni6 cuboctahedra.