Nd2Fe15(SiH)2 crystallizes in the monoclinic C2/m space group. Nd(1) is bonded in a distorted bent 120 degrees geometry to one Fe(3), two equivalent Fe(1), two equivalent Fe(4), three equivalent Fe(5), one Si(1), and two equivalent H(1) atoms. There are six inequivalent Fe sites. In the first Fe site, Fe(1) is bonded to two equivalent Nd(1), two equivalent Fe(2), two equivalent Fe(4), two equivalent Fe(5), two equivalent Fe(6), and two equivalent Si(1) atoms to form distorted FeNd2Fe8Si2 cuboctahedra that share corners with two equivalent Fe(1)Nd2Fe8Si2 cuboctahedra, corners with two equivalent Fe(3)Nd2Fe8Si2 cuboctahedra, corners with two equivalent Fe(4)Nd2Fe8Si2 cuboctahedra, corners with two equivalent Fe(5)Nd3Fe8Si cuboctahedra, corners with four equivalent H(1)Nd2Fe4 octahedra,  an edgeedge with one Fe(1)Nd2Fe8Si2 cuboctahedra, edges with two equivalent Fe(4)Nd2Fe8Si2 cuboctahedra, edges with two equivalent H(1)Nd2Fe4 octahedra,  a faceface with one Fe(1)Nd2Fe8Si2 cuboctahedra, faces with two equivalent Fe(3)Nd2Fe8Si2 cuboctahedra, faces with two equivalent Fe(4)Nd2Fe8Si2 cuboctahedra, and faces with four equivalent Fe(5)Nd3Fe8Si cuboctahedra. The corner-sharing octahedral tilt angles range from 24-29°. In the second Fe site, Fe(2) is bonded in a single-bond geometry to one Fe(1), one Fe(3), one Fe(4), one Fe(5), two equivalent Si(1), and one H(1) atom. In the third Fe site, Fe(3) is bonded to two equivalent Nd(1), four equivalent Fe(2), four equivalent Fe(6), and two equivalent Si(1) atoms to form distorted FeNd2Fe8Si2 cuboctahedra that share corners with four equivalent Fe(1)Nd2Fe8Si2 cuboctahedra, corners with four equivalent Fe(4)Nd2Fe8Si2 cuboctahedra, corners with six equivalent Fe(5)Nd3Fe8Si cuboctahedra, edges with two equivalent Fe(5)Nd3Fe8Si cuboctahedra, faces with two equivalent Fe(5)Nd3Fe8Si cuboctahedra, faces with four equivalent Fe(1)Nd2Fe8Si2 cuboctahedra, faces with four equivalent Fe(4)Nd2Fe8Si2 cuboctahedra, and faces with four equivalent H(1)Nd2Fe4 octahedra. In the fourth Fe site, Fe(4) is bonded to two equivalent Nd(1), two equivalent Fe(1), two equivalent Fe(2), two equivalent Fe(5), two equivalent Fe(6), and two equivalent Si(1) atoms to form distorted FeNd2Fe8Si2 cuboctahedra that share corners with two equivalent Fe(1)Nd2Fe8Si2 cuboctahedra, corners with two equivalent Fe(3)Nd2Fe8Si2 cuboctahedra, corners with two equivalent Fe(4)Nd2Fe8Si2 cuboctahedra, corners with two equivalent Fe(5)Nd3Fe8Si cuboctahedra, corners with two equivalent H(1)Nd2Fe4 octahedra, edges with two equivalent Fe(1)Nd2Fe8Si2 cuboctahedra, edges with two equivalent Fe(5)Nd3Fe8Si cuboctahedra, faces with two equivalent Fe(1)Nd2Fe8Si2 cuboctahedra, faces with two equivalent Fe(3)Nd2Fe8Si2 cuboctahedra, faces with two equivalent Fe(4)Nd2Fe8Si2 cuboctahedra, faces with two equivalent Fe(5)Nd3Fe8Si cuboctahedra, and faces with two equivalent H(1)Nd2Fe4 octahedra. The corner-sharing octahedral tilt angles are 47°. In the fifth Fe site, Fe(5) is bonded to three equivalent Nd(1), two equivalent Fe(1), two equivalent Fe(2), two equivalent Fe(4), two equivalent Fe(6), and one Si(1) atom to form FeNd3Fe8Si cuboctahedra that share corners with two equivalent Fe(1)Nd2Fe8Si2 cuboctahedra, corners with two equivalent Fe(4)Nd2Fe8Si2 cuboctahedra, corners with three equivalent Fe(3)Nd2Fe8Si2 cuboctahedra, corners with four equivalent Fe(5)Nd3Fe8Si cuboctahedra, corners with four equivalent H(1)Nd2Fe4 octahedra,  an edgeedge with one Fe(3)Nd2Fe8Si2 cuboctahedra,  an edgeedge with one Fe(5)Nd3Fe8Si cuboctahedra, edges with two equivalent Fe(4)Nd2Fe8Si2 cuboctahedra,  a faceface with one Fe(3)Nd2Fe8Si2 cuboctahedra,  a faceface with one Fe(5)Nd3Fe8Si cuboctahedra, faces with two equivalent Fe(4)Nd2Fe8Si2 cuboctahedra, faces with four equivalent Fe(1)Nd2Fe8Si2 cuboctahedra, and faces with two equivalent H(1)Nd2Fe4 octahedra. The corner-sharing octahedral tilt angles range from 63-71°. In the sixth Fe site, Fe(6) is bonded in a single-bond geometry to one Fe(1), one Fe(3), one Fe(4), one Fe(5), one Si(1), and one H(1) atom. Si(1) is bonded in a 14-coordinate geometry to one Nd(1), one Fe(3), one Fe(5), two equivalent Fe(1), two equivalent Fe(4), two equivalent Fe(6), four equivalent Fe(2), and one Si(1) atom. H(1) is bonded to two equivalent Nd(1), two equivalent Fe(2), and two equivalent Fe(6) atoms to form HNd2Fe4 octahedra that share corners with two equivalent Fe(4)Nd2Fe8Si2 cuboctahedra, corners with four equivalent Fe(1)Nd2Fe8Si2 cuboctahedra, corners with four equivalent Fe(5)Nd3Fe8Si cuboctahedra, corners with two equivalent H(1)Nd2Fe4 octahedra, edges with two equivalent Fe(1)Nd2Fe8Si2 cuboctahedra, faces with two equivalent Fe(3)Nd2Fe8Si2 cuboctahedra, faces with two equivalent Fe(4)Nd2Fe8Si2 cuboctahedra, and faces with two equivalent Fe(5)Nd3Fe8Si cuboctahedra. The corner-sharing octahedral tilt angles are 61°.
Nd2Fe15(SiH)2 crystallizes in the monoclinic C2/m space group. Nd(1) is bonded in a distorted bent 120 degrees geometry to one Fe(3), two equivalent Fe(1), two equivalent Fe(4), three equivalent Fe(5), one Si(1), and two equivalent H(1) atoms. The Nd(1)-Fe(3) bond length is 3.35 Å. Both Nd(1)-Fe(1) bond lengths are 3.05 Å. Both Nd(1)-Fe(4) bond lengths are 3.34 Å. There are a spread of Nd(1)-Fe(5) bond distances ranging from 3.06-3.23 Å. The Nd(1)-Si(1) bond length is 3.09 Å. Both Nd(1)-H(1) bond lengths are 2.46 Å. There are six inequivalent Fe sites. In the first Fe site, Fe(1) is bonded to two equivalent Nd(1), two equivalent Fe(2), two equivalent Fe(4), two equivalent Fe(5), two equivalent Fe(6), and two equivalent Si(1) atoms to form distorted FeNd2Fe8Si2 cuboctahedra that share corners with two equivalent Fe(1)Nd2Fe8Si2 cuboctahedra, corners with two equivalent Fe(3)Nd2Fe8Si2 cuboctahedra, corners with two equivalent Fe(4)Nd2Fe8Si2 cuboctahedra, corners with two equivalent Fe(5)Nd3Fe8Si cuboctahedra, corners with four equivalent H(1)Nd2Fe4 octahedra,  an edgeedge with one Fe(1)Nd2Fe8Si2 cuboctahedra, edges with two equivalent Fe(4)Nd2Fe8Si2 cuboctahedra, edges with two equivalent H(1)Nd2Fe4 octahedra,  a faceface with one Fe(1)Nd2Fe8Si2 cuboctahedra, faces with two equivalent Fe(3)Nd2Fe8Si2 cuboctahedra, faces with two equivalent Fe(4)Nd2Fe8Si2 cuboctahedra, and faces with four equivalent Fe(5)Nd3Fe8Si cuboctahedra. The corner-sharing octahedral tilt angles range from 24-29°. Both Fe(1)-Fe(2) bond lengths are 2.40 Å. Both Fe(1)-Fe(4) bond lengths are 2.44 Å. Both Fe(1)-Fe(5) bond lengths are 2.70 Å. Both Fe(1)-Fe(6) bond lengths are 2.54 Å. Both Fe(1)-Si(1) bond lengths are 2.74 Å. In the second Fe site, Fe(2) is bonded in a single-bond geometry to one Fe(1), one Fe(3), one Fe(4), one Fe(5), two equivalent Si(1), and one H(1) atom. The Fe(2)-Fe(3) bond length is 2.44 Å. The Fe(2)-Fe(4) bond length is 2.44 Å. The Fe(2)-Fe(5) bond length is 2.52 Å. There is one shorter (2.70 Å) and one longer (2.71 Å) Fe(2)-Si(1) bond length. The Fe(2)-H(1) bond length is 1.86 Å. In the third Fe site, Fe(3) is bonded to two equivalent Nd(1), four equivalent Fe(2), four equivalent Fe(6), and two equivalent Si(1) atoms to form distorted FeNd2Fe8Si2 cuboctahedra that share corners with four equivalent Fe(1)Nd2Fe8Si2 cuboctahedra, corners with four equivalent Fe(4)Nd2Fe8Si2 cuboctahedra, corners with six equivalent Fe(5)Nd3Fe8Si cuboctahedra, edges with two equivalent Fe(5)Nd3Fe8Si cuboctahedra, faces with two equivalent Fe(5)Nd3Fe8Si cuboctahedra, faces with four equivalent Fe(1)Nd2Fe8Si2 cuboctahedra, faces with four equivalent Fe(4)Nd2Fe8Si2 cuboctahedra, and faces with four equivalent H(1)Nd2Fe4 octahedra. All Fe(3)-Fe(6) bond lengths are 2.43 Å. Both Fe(3)-Si(1) bond lengths are 2.58 Å. In the fourth Fe site, Fe(4) is bonded to two equivalent Nd(1), two equivalent Fe(1), two equivalent Fe(2), two equivalent Fe(5), two equivalent Fe(6), and two equivalent Si(1) atoms to form distorted FeNd2Fe8Si2 cuboctahedra that share corners with two equivalent Fe(1)Nd2Fe8Si2 cuboctahedra, corners with two equivalent Fe(3)Nd2Fe8Si2 cuboctahedra, corners with two equivalent Fe(4)Nd2Fe8Si2 cuboctahedra, corners with two equivalent Fe(5)Nd3Fe8Si cuboctahedra, corners with two equivalent H(1)Nd2Fe4 octahedra, edges with two equivalent Fe(1)Nd2Fe8Si2 cuboctahedra, edges with two equivalent Fe(5)Nd3Fe8Si cuboctahedra, faces with two equivalent Fe(1)Nd2Fe8Si2 cuboctahedra, faces with two equivalent Fe(3)Nd2Fe8Si2 cuboctahedra, faces with two equivalent Fe(4)Nd2Fe8Si2 cuboctahedra, faces with two equivalent Fe(5)Nd3Fe8Si cuboctahedra, and faces with two equivalent H(1)Nd2Fe4 octahedra. The corner-sharing octahedral tilt angles are 47°. Both Fe(4)-Fe(5) bond lengths are 2.43 Å. Both Fe(4)-Fe(6) bond lengths are 2.43 Å. Both Fe(4)-Si(1) bond lengths are 2.58 Å. In the fifth Fe site, Fe(5) is bonded to three equivalent Nd(1), two equivalent Fe(1), two equivalent Fe(2), two equivalent Fe(4), two equivalent Fe(6), and one Si(1) atom to form FeNd3Fe8Si cuboctahedra that share corners with two equivalent Fe(1)Nd2Fe8Si2 cuboctahedra, corners with two equivalent Fe(4)Nd2Fe8Si2 cuboctahedra, corners with three equivalent Fe(3)Nd2Fe8Si2 cuboctahedra, corners with four equivalent Fe(5)Nd3Fe8Si cuboctahedra, corners with four equivalent H(1)Nd2Fe4 octahedra,  an edgeedge with one Fe(3)Nd2Fe8Si2 cuboctahedra,  an edgeedge with one Fe(5)Nd3Fe8Si cuboctahedra, edges with two equivalent Fe(4)Nd2Fe8Si2 cuboctahedra,  a faceface with one Fe(3)Nd2Fe8Si2 cuboctahedra,  a faceface with one Fe(5)Nd3Fe8Si cuboctahedra, faces with two equivalent Fe(4)Nd2Fe8Si2 cuboctahedra, faces with four equivalent Fe(1)Nd2Fe8Si2 cuboctahedra, and faces with two equivalent H(1)Nd2Fe4 octahedra. The corner-sharing octahedral tilt angles range from 63-71°. Both Fe(5)-Fe(6) bond lengths are 2.50 Å. The Fe(5)-Si(1) bond length is 2.58 Å. In the sixth Fe site, Fe(6) is bonded in a single-bond geometry to one Fe(1), one Fe(3), one Fe(4), one Fe(5), one Si(1), and one H(1) atom. The Fe(6)-Si(1) bond length is 2.58 Å. The Fe(6)-H(1) bond length is 1.98 Å. Si(1) is bonded in a 14-coordinate geometry to one Nd(1), one Fe(3), one Fe(5), two equivalent Fe(1), two equivalent Fe(4), two equivalent Fe(6), four equivalent Fe(2), and one Si(1) atom. The Si(1)-Si(1) bond length is 2.55 Å. H(1) is bonded to two equivalent Nd(1), two equivalent Fe(2), and two equivalent Fe(6) atoms to form HNd2Fe4 octahedra that share corners with two equivalent Fe(4)Nd2Fe8Si2 cuboctahedra, corners with four equivalent Fe(1)Nd2Fe8Si2 cuboctahedra, corners with four equivalent Fe(5)Nd3Fe8Si cuboctahedra, corners with two equivalent H(1)Nd2Fe4 octahedra, edges with two equivalent Fe(1)Nd2Fe8Si2 cuboctahedra, faces with two equivalent Fe(3)Nd2Fe8Si2 cuboctahedra, faces with two equivalent Fe(4)Nd2Fe8Si2 cuboctahedra, and faces with two equivalent Fe(5)Nd3Fe8Si cuboctahedra. The corner-sharing octahedral tilt angles are 61°.