Mg2Ni3Si crystallizes in the trigonal R-3m space group. Mg(1) is bonded in a 16-coordinate geometry to four equivalent Mg(1), nine equivalent Ni(1), and three equivalent Si(1) atoms. Ni(1) is bonded to six equivalent Mg(1), four equivalent Ni(1), and two equivalent Si(1) atoms to form NiMg6Si2Ni4 cuboctahedra that share corners with four equivalent Si(1)Mg6Ni6 cuboctahedra, corners with fourteen equivalent Ni(1)Mg6Si2Ni4 cuboctahedra, edges with six equivalent Ni(1)Mg6Si2Ni4 cuboctahedra, faces with six equivalent Si(1)Mg6Ni6 cuboctahedra, and faces with twelve equivalent Ni(1)Mg6Si2Ni4 cuboctahedra. Si(1) is bonded to six equivalent Mg(1) and six equivalent Ni(1) atoms to form SiMg6Ni6 cuboctahedra that share corners with six equivalent Si(1)Mg6Ni6 cuboctahedra, corners with twelve equivalent Ni(1)Mg6Si2Ni4 cuboctahedra, edges with six equivalent Si(1)Mg6Ni6 cuboctahedra, and faces with eighteen equivalent Ni(1)Mg6Si2Ni4 cuboctahedra.
Mg2Ni3Si crystallizes in the trigonal R-3m space group. Mg(1) is bonded in a 16-coordinate geometry to four equivalent Mg(1), nine equivalent Ni(1), and three equivalent Si(1) atoms. There is one shorter (2.75 Å) and three longer (3.00 Å) Mg(1)-Mg(1) bond lengths. There are three shorter (2.69 Å) and six longer (2.83 Å) Mg(1)-Ni(1) bond lengths. All Mg(1)-Si(1) bond lengths are 2.89 Å. Ni(1) is bonded to six equivalent Mg(1), four equivalent Ni(1), and two equivalent Si(1) atoms to form NiMg6Si2Ni4 cuboctahedra that share corners with four equivalent Si(1)Mg6Ni6 cuboctahedra, corners with fourteen equivalent Ni(1)Mg6Si2Ni4 cuboctahedra, edges with six equivalent Ni(1)Mg6Si2Ni4 cuboctahedra, faces with six equivalent Si(1)Mg6Ni6 cuboctahedra, and faces with twelve equivalent Ni(1)Mg6Si2Ni4 cuboctahedra. All Ni(1)-Ni(1) bond lengths are 2.47 Å. Both Ni(1)-Si(1) bond lengths are 2.32 Å. Si(1) is bonded to six equivalent Mg(1) and six equivalent Ni(1) atoms to form SiMg6Ni6 cuboctahedra that share corners with six equivalent Si(1)Mg6Ni6 cuboctahedra, corners with twelve equivalent Ni(1)Mg6Si2Ni4 cuboctahedra, edges with six equivalent Si(1)Mg6Ni6 cuboctahedra, and faces with eighteen equivalent Ni(1)Mg6Si2Ni4 cuboctahedra.