NiP4 crystallizes in the monoclinic P2_1/c space group. There are two inequivalent Ni sites. In the first Ni site, Ni(1) is bonded to two equivalent P(2), two equivalent P(3), and two equivalent P(4) atoms to form NiP6 octahedra that share corners with two equivalent P(1)Ni2P2 tetrahedra, corners with two equivalent P(2)Ni2P2 tetrahedra, corners with two equivalent P(4)Ni2P2 tetrahedra, corners with four equivalent P(5)NiP3 tetrahedra, corners with four equivalent P(6)NiP3 tetrahedra, and edges with two equivalent Ni(2)P6 octahedra. In the second Ni site, Ni(2) is bonded to one P(2), one P(4), one P(5), one P(6), and two equivalent P(1) atoms to form NiP6 octahedra that share corners with two equivalent Ni(2)P6 octahedra,  a cornercorner with one P(1)Ni2P2 tetrahedra, corners with two equivalent P(2)Ni2P2 tetrahedra, corners with two equivalent P(4)Ni2P2 tetrahedra, corners with two equivalent P(5)NiP3 tetrahedra, corners with three equivalent P(6)NiP3 tetrahedra, corners with four equivalent P(3)NiP3 tetrahedra, and  an edgeedge with one Ni(1)P6 octahedra. The corner-sharing octahedral tilt angles are 55°. There are six inequivalent P sites. In the first P site, P(1) is bonded to two equivalent Ni(2), one P(3), and one P(6) atom to form distorted PNi2P2 tetrahedra that share  a cornercorner with one Ni(1)P6 octahedra,  a cornercorner with one Ni(2)P6 octahedra,  a cornercorner with one P(3)NiP3 tetrahedra, corners with two equivalent P(1)Ni2P2 tetrahedra, corners with two equivalent P(2)Ni2P2 tetrahedra, corners with three equivalent P(4)Ni2P2 tetrahedra, corners with three equivalent P(5)NiP3 tetrahedra, and corners with three equivalent P(6)NiP3 tetrahedra. The corner-sharing octahedral tilt angles range from 53-64°. In the second P site, P(2) is bonded to one Ni(1), one Ni(2), one P(4), and one P(5) atom to form distorted PNi2P2 tetrahedra that share  a cornercorner with one Ni(1)P6 octahedra, corners with two equivalent Ni(2)P6 octahedra,  a cornercorner with one P(2)Ni2P2 tetrahedra,  a cornercorner with one P(4)Ni2P2 tetrahedra, corners with two equivalent P(1)Ni2P2 tetrahedra, corners with two equivalent P(5)NiP3 tetrahedra, corners with two equivalent P(6)NiP3 tetrahedra, corners with three equivalent P(3)NiP3 tetrahedra, and  an edgeedge with one P(4)Ni2P2 tetrahedra. The corner-sharing octahedral tilt angles range from 51-66°. In the third P site, P(3) is bonded to one Ni(1), one P(1), one P(5), and one P(6) atom to form distorted PNiP3 tetrahedra that share corners with four equivalent Ni(2)P6 octahedra,  a cornercorner with one P(1)Ni2P2 tetrahedra,  a cornercorner with one P(3)NiP3 tetrahedra,  a cornercorner with one P(5)NiP3 tetrahedra,  a cornercorner with one P(6)NiP3 tetrahedra, corners with three equivalent P(2)Ni2P2 tetrahedra, and corners with three equivalent P(4)Ni2P2 tetrahedra. The corner-sharing octahedral tilt angles range from 42-79°. In the fourth P site, P(4) is bonded to one Ni(1), one Ni(2), one P(2), and one P(6) atom to form distorted PNi2P2 tetrahedra that share  a cornercorner with one Ni(1)P6 octahedra, corners with two equivalent Ni(2)P6 octahedra,  a cornercorner with one P(2)Ni2P2 tetrahedra,  a cornercorner with one P(4)Ni2P2 tetrahedra,  a cornercorner with one P(6)NiP3 tetrahedra, corners with two equivalent P(5)NiP3 tetrahedra, corners with three equivalent P(1)Ni2P2 tetrahedra, corners with three equivalent P(3)NiP3 tetrahedra, and  an edgeedge with one P(2)Ni2P2 tetrahedra. The corner-sharing octahedral tilt angles range from 65-73°. In the fifth P site, P(5) is bonded to one Ni(2), one P(2), one P(3), and one P(5) atom to form distorted PNiP3 tetrahedra that share corners with two equivalent Ni(1)P6 octahedra, corners with two equivalent Ni(2)P6 octahedra,  a cornercorner with one P(3)NiP3 tetrahedra, corners with two equivalent P(2)Ni2P2 tetrahedra, corners with two equivalent P(4)Ni2P2 tetrahedra, corners with two equivalent P(6)NiP3 tetrahedra, and corners with three equivalent P(1)Ni2P2 tetrahedra. The corner-sharing octahedral tilt angles range from 57-66°. In the sixth P site, P(6) is bonded to one Ni(2), one P(1), one P(3), and one P(4) atom to form distorted PNiP3 tetrahedra that share corners with two equivalent Ni(1)P6 octahedra, corners with three equivalent Ni(2)P6 octahedra,  a cornercorner with one P(4)Ni2P2 tetrahedra,  a cornercorner with one P(3)NiP3 tetrahedra, corners with two equivalent P(2)Ni2P2 tetrahedra, corners with two equivalent P(5)NiP3 tetrahedra, and corners with three equivalent P(1)Ni2P2 tetrahedra. The corner-sharing octahedral tilt angles range from 61-78°.
NiP4 crystallizes in the monoclinic P2_1/c space group. There are two inequivalent Ni sites. In the first Ni site, Ni(1) is bonded to two equivalent P(2), two equivalent P(3), and two equivalent P(4) atoms to form NiP6 octahedra that share corners with two equivalent P(1)Ni2P2 tetrahedra, corners with two equivalent P(2)Ni2P2 tetrahedra, corners with two equivalent P(4)Ni2P2 tetrahedra, corners with four equivalent P(5)NiP3 tetrahedra, corners with four equivalent P(6)NiP3 tetrahedra, and edges with two equivalent Ni(2)P6 octahedra. Both Ni(1)-P(2) bond lengths are 2.29 Å. Both Ni(1)-P(3) bond lengths are 2.34 Å. Both Ni(1)-P(4) bond lengths are 2.33 Å. In the second Ni site, Ni(2) is bonded to one P(2), one P(4), one P(5), one P(6), and two equivalent P(1) atoms to form NiP6 octahedra that share corners with two equivalent Ni(2)P6 octahedra,  a cornercorner with one P(1)Ni2P2 tetrahedra, corners with two equivalent P(2)Ni2P2 tetrahedra, corners with two equivalent P(4)Ni2P2 tetrahedra, corners with two equivalent P(5)NiP3 tetrahedra, corners with three equivalent P(6)NiP3 tetrahedra, corners with four equivalent P(3)NiP3 tetrahedra, and  an edgeedge with one Ni(1)P6 octahedra. The corner-sharing octahedral tilt angles are 55°. The Ni(2)-P(2) bond length is 2.41 Å. The Ni(2)-P(4) bond length is 2.33 Å. The Ni(2)-P(5) bond length is 2.25 Å. The Ni(2)-P(6) bond length is 2.32 Å. There is one shorter (2.33 Å) and one longer (2.36 Å) Ni(2)-P(1) bond length. There are six inequivalent P sites. In the first P site, P(1) is bonded to two equivalent Ni(2), one P(3), and one P(6) atom to form distorted PNi2P2 tetrahedra that share  a cornercorner with one Ni(1)P6 octahedra,  a cornercorner with one Ni(2)P6 octahedra,  a cornercorner with one P(3)NiP3 tetrahedra, corners with two equivalent P(1)Ni2P2 tetrahedra, corners with two equivalent P(2)Ni2P2 tetrahedra, corners with three equivalent P(4)Ni2P2 tetrahedra, corners with three equivalent P(5)NiP3 tetrahedra, and corners with three equivalent P(6)NiP3 tetrahedra. The corner-sharing octahedral tilt angles range from 53-64°. The P(1)-P(3) bond length is 2.24 Å. The P(1)-P(6) bond length is 2.27 Å. In the second P site, P(2) is bonded to one Ni(1), one Ni(2), one P(4), and one P(5) atom to form distorted PNi2P2 tetrahedra that share  a cornercorner with one Ni(1)P6 octahedra, corners with two equivalent Ni(2)P6 octahedra,  a cornercorner with one P(2)Ni2P2 tetrahedra,  a cornercorner with one P(4)Ni2P2 tetrahedra, corners with two equivalent P(1)Ni2P2 tetrahedra, corners with two equivalent P(5)NiP3 tetrahedra, corners with two equivalent P(6)NiP3 tetrahedra, corners with three equivalent P(3)NiP3 tetrahedra, and  an edgeedge with one P(4)Ni2P2 tetrahedra. The corner-sharing octahedral tilt angles range from 51-66°. The P(2)-P(4) bond length is 2.21 Å. The P(2)-P(5) bond length is 2.20 Å. In the third P site, P(3) is bonded to one Ni(1), one P(1), one P(5), and one P(6) atom to form distorted PNiP3 tetrahedra that share corners with four equivalent Ni(2)P6 octahedra,  a cornercorner with one P(1)Ni2P2 tetrahedra,  a cornercorner with one P(3)NiP3 tetrahedra,  a cornercorner with one P(5)NiP3 tetrahedra,  a cornercorner with one P(6)NiP3 tetrahedra, corners with three equivalent P(2)Ni2P2 tetrahedra, and corners with three equivalent P(4)Ni2P2 tetrahedra. The corner-sharing octahedral tilt angles range from 42-79°. The P(3)-P(5) bond length is 2.27 Å. The P(3)-P(6) bond length is 2.28 Å. In the fourth P site, P(4) is bonded to one Ni(1), one Ni(2), one P(2), and one P(6) atom to form distorted PNi2P2 tetrahedra that share  a cornercorner with one Ni(1)P6 octahedra, corners with two equivalent Ni(2)P6 octahedra,  a cornercorner with one P(2)Ni2P2 tetrahedra,  a cornercorner with one P(4)Ni2P2 tetrahedra,  a cornercorner with one P(6)NiP3 tetrahedra, corners with two equivalent P(5)NiP3 tetrahedra, corners with three equivalent P(1)Ni2P2 tetrahedra, corners with three equivalent P(3)NiP3 tetrahedra, and  an edgeedge with one P(2)Ni2P2 tetrahedra. The corner-sharing octahedral tilt angles range from 65-73°. The P(4)-P(6) bond length is 2.21 Å. In the fifth P site, P(5) is bonded to one Ni(2), one P(2), one P(3), and one P(5) atom to form distorted PNiP3 tetrahedra that share corners with two equivalent Ni(1)P6 octahedra, corners with two equivalent Ni(2)P6 octahedra,  a cornercorner with one P(3)NiP3 tetrahedra, corners with two equivalent P(2)Ni2P2 tetrahedra, corners with two equivalent P(4)Ni2P2 tetrahedra, corners with two equivalent P(6)NiP3 tetrahedra, and corners with three equivalent P(1)Ni2P2 tetrahedra. The corner-sharing octahedral tilt angles range from 57-66°. The P(5)-P(5) bond length is 2.30 Å. In the sixth P site, P(6) is bonded to one Ni(2), one P(1), one P(3), and one P(4) atom to form distorted PNiP3 tetrahedra that share corners with two equivalent Ni(1)P6 octahedra, corners with three equivalent Ni(2)P6 octahedra,  a cornercorner with one P(4)Ni2P2 tetrahedra,  a cornercorner with one P(3)NiP3 tetrahedra, corners with two equivalent P(2)Ni2P2 tetrahedra, corners with two equivalent P(5)NiP3 tetrahedra, and corners with three equivalent P(1)Ni2P2 tetrahedra. The corner-sharing octahedral tilt angles range from 61-78°.