Pr2MgNi9 is Frank-Kasper $\mu$ Phase-derived structured and crystallizes in the trigonal R3m space group. Mg(1) is bonded in a 16-coordinate geometry to one Pr(1), three equivalent Pr(2), three equivalent Ni(1), three equivalent Ni(3), and six equivalent Ni(2) atoms. There are two inequivalent Pr sites. In the first Pr site, Pr(1) is bonded in a 6-coordinate geometry to one Mg(1), three equivalent Ni(4), three equivalent Ni(5), six equivalent Ni(1), and six equivalent Ni(2) atoms. In the second Pr site, Pr(2) is bonded in a 15-coordinate geometry to three equivalent Mg(1), three equivalent Ni(2), three equivalent Ni(3), and six equivalent Ni(1) atoms. There are five inequivalent Ni sites. In the first Ni site, Ni(1) is bonded to one Mg(1), two equivalent Pr(1), two equivalent Pr(2), one Ni(3), one Ni(4), one Ni(5), and four equivalent Ni(1) atoms to form distorted NiPr4MgNi7 cuboctahedra that share corners with two equivalent Ni(3)Pr3Mg3Ni6 cuboctahedra, corners with four equivalent Ni(1)Pr4MgNi7 cuboctahedra, corners with eleven equivalent Ni(2)Pr3Mg2Ni7 cuboctahedra, edges with two equivalent Ni(1)Pr4MgNi7 cuboctahedra, edges with six equivalent Ni(2)Pr3Mg2Ni7 cuboctahedra, faces with three equivalent Ni(2)Pr3Mg2Ni7 cuboctahedra, faces with three equivalent Ni(3)Pr3Mg3Ni6 cuboctahedra, and faces with eight equivalent Ni(1)Pr4MgNi7 cuboctahedra. In the second Ni site, Ni(2) is bonded to two equivalent Mg(1), one Pr(2), two equivalent Pr(1), one Ni(3), one Ni(4), one Ni(5), and four equivalent Ni(2) atoms to form NiPr3Mg2Ni7 cuboctahedra that share corners with two equivalent Ni(3)Pr3Mg3Ni6 cuboctahedra, corners with four equivalent Ni(2)Pr3Mg2Ni7 cuboctahedra, corners with eleven equivalent Ni(1)Pr4MgNi7 cuboctahedra, edges with two equivalent Ni(2)Pr3Mg2Ni7 cuboctahedra, edges with six equivalent Ni(1)Pr4MgNi7 cuboctahedra, faces with three equivalent Ni(3)Pr3Mg3Ni6 cuboctahedra, faces with three equivalent Ni(1)Pr4MgNi7 cuboctahedra, and faces with eight equivalent Ni(2)Pr3Mg2Ni7 cuboctahedra. In the third Ni site, Ni(3) is bonded to three equivalent Mg(1), three equivalent Pr(2), three equivalent Ni(1), and three equivalent Ni(2) atoms to form NiPr3Mg3Ni6 cuboctahedra that share corners with six equivalent Ni(2)Pr3Mg2Ni7 cuboctahedra, corners with six equivalent Ni(1)Pr4MgNi7 cuboctahedra, edges with six equivalent Ni(3)Pr3Mg3Ni6 cuboctahedra, faces with nine equivalent Ni(2)Pr3Mg2Ni7 cuboctahedra, and faces with nine equivalent Ni(1)Pr4MgNi7 cuboctahedra. In the fourth Ni site, Ni(4) is bonded in a 9-coordinate geometry to three equivalent Pr(1), three equivalent Ni(1), and three equivalent Ni(2) atoms. In the fifth Ni site, Ni(5) is bonded in a 9-coordinate geometry to three equivalent Pr(1), three equivalent Ni(1), and three equivalent Ni(2) atoms.
Pr2MgNi9 is Frank-Kasper $\mu$ Phase-derived structured and crystallizes in the trigonal R3m space group. Mg(1) is bonded in a 16-coordinate geometry to one Pr(1), three equivalent Pr(2), three equivalent Ni(1), three equivalent Ni(3), and six equivalent Ni(2) atoms. The Mg(1)-Pr(1) bond length is 3.25 Å. All Mg(1)-Pr(2) bond lengths are 3.14 Å. All Mg(1)-Ni(1) bond lengths are 3.07 Å. All Mg(1)-Ni(3) bond lengths are 2.95 Å. All Mg(1)-Ni(2) bond lengths are 2.84 Å. There are two inequivalent Pr sites. In the first Pr site, Pr(1) is bonded in a 6-coordinate geometry to one Mg(1), three equivalent Ni(4), three equivalent Ni(5), six equivalent Ni(1), and six equivalent Ni(2) atoms. All Pr(1)-Ni(4) bond lengths are 2.88 Å. All Pr(1)-Ni(5) bond lengths are 2.89 Å. All Pr(1)-Ni(1) bond lengths are 3.26 Å. All Pr(1)-Ni(2) bond lengths are 3.13 Å. In the second Pr site, Pr(2) is bonded in a 15-coordinate geometry to three equivalent Mg(1), three equivalent Ni(2), three equivalent Ni(3), and six equivalent Ni(1) atoms. All Pr(2)-Ni(2) bond lengths are 2.97 Å. All Pr(2)-Ni(3) bond lengths are 2.94 Å. All Pr(2)-Ni(1) bond lengths are 2.90 Å. There are five inequivalent Ni sites. In the first Ni site, Ni(1) is bonded to one Mg(1), two equivalent Pr(1), two equivalent Pr(2), one Ni(3), one Ni(4), one Ni(5), and four equivalent Ni(1) atoms to form distorted NiPr4MgNi7 cuboctahedra that share corners with two equivalent Ni(3)Pr3Mg3Ni6 cuboctahedra, corners with four equivalent Ni(1)Pr4MgNi7 cuboctahedra, corners with eleven equivalent Ni(2)Pr3Mg2Ni7 cuboctahedra, edges with two equivalent Ni(1)Pr4MgNi7 cuboctahedra, edges with six equivalent Ni(2)Pr3Mg2Ni7 cuboctahedra, faces with three equivalent Ni(2)Pr3Mg2Ni7 cuboctahedra, faces with three equivalent Ni(3)Pr3Mg3Ni6 cuboctahedra, and faces with eight equivalent Ni(1)Pr4MgNi7 cuboctahedra. The Ni(1)-Ni(3) bond length is 2.52 Å. The Ni(1)-Ni(4) bond length is 2.46 Å. The Ni(1)-Ni(5) bond length is 2.44 Å. There are two shorter (2.49 Å) and two longer (2.50 Å) Ni(1)-Ni(1) bond lengths. In the second Ni site, Ni(2) is bonded to two equivalent Mg(1), one Pr(2), two equivalent Pr(1), one Ni(3), one Ni(4), one Ni(5), and four equivalent Ni(2) atoms to form NiPr3Mg2Ni7 cuboctahedra that share corners with two equivalent Ni(3)Pr3Mg3Ni6 cuboctahedra, corners with four equivalent Ni(2)Pr3Mg2Ni7 cuboctahedra, corners with eleven equivalent Ni(1)Pr4MgNi7 cuboctahedra, edges with two equivalent Ni(2)Pr3Mg2Ni7 cuboctahedra, edges with six equivalent Ni(1)Pr4MgNi7 cuboctahedra, faces with three equivalent Ni(3)Pr3Mg3Ni6 cuboctahedra, faces with three equivalent Ni(1)Pr4MgNi7 cuboctahedra, and faces with eight equivalent Ni(2)Pr3Mg2Ni7 cuboctahedra. The Ni(2)-Ni(3) bond length is 2.46 Å. The Ni(2)-Ni(4) bond length is 2.47 Å. The Ni(2)-Ni(5) bond length is 2.48 Å. There are two shorter (2.49 Å) and two longer (2.50 Å) Ni(2)-Ni(2) bond lengths. In the third Ni site, Ni(3) is bonded to three equivalent Mg(1), three equivalent Pr(2), three equivalent Ni(1), and three equivalent Ni(2) atoms to form NiPr3Mg3Ni6 cuboctahedra that share corners with six equivalent Ni(2)Pr3Mg2Ni7 cuboctahedra, corners with six equivalent Ni(1)Pr4MgNi7 cuboctahedra, edges with six equivalent Ni(3)Pr3Mg3Ni6 cuboctahedra, faces with nine equivalent Ni(2)Pr3Mg2Ni7 cuboctahedra, and faces with nine equivalent Ni(1)Pr4MgNi7 cuboctahedra. In the fourth Ni site, Ni(4) is bonded in a 9-coordinate geometry to three equivalent Pr(1), three equivalent Ni(1), and three equivalent Ni(2) atoms. In the fifth Ni site, Ni(5) is bonded in a 9-coordinate geometry to three equivalent Pr(1), three equivalent Ni(1), and three equivalent Ni(2) atoms.