Y2Fe4Si9 crystallizes in the trigonal P-3m1 space group. Y(1) is bonded in a 6-coordinate geometry to three equivalent Fe(2), one Si(3), one Si(4), three equivalent Si(1), and three equivalent Si(2) atoms. There are two inequivalent Fe sites. In the first Fe site, Fe(1) is bonded in a 7-coordinate geometry to three equivalent Si(1), three equivalent Si(5), and four equivalent Si(3) atoms. In the second Fe site, Fe(2) is bonded in a 10-coordinate geometry to three equivalent Y(1), three equivalent Si(2), and four equivalent Si(4) atoms. There are five inequivalent Si sites. In the first Si site, Si(1) is bonded in a 10-coordinate geometry to three equivalent Y(1), three equivalent Fe(1), one Si(5), and three equivalent Si(3) atoms. In the second Si site, Si(2) is bonded in a 9-coordinate geometry to three equivalent Y(1), three equivalent Fe(2), and three equivalent Si(4) atoms. In the third Si site, Si(3) is bonded in a 11-coordinate geometry to one Y(1), four equivalent Fe(1), three equivalent Si(1), and three equivalent Si(5) atoms. In the fourth Si site, Si(4) is bonded in a 11-coordinate geometry to one Y(1), four equivalent Fe(2), three equivalent Si(2), and three equivalent Si(4) atoms. In the fifth Si site, Si(5) is bonded in a 14-coordinate geometry to six equivalent Fe(1), two equivalent Si(1), and six equivalent Si(3) atoms.
Y2Fe4Si9 crystallizes in the trigonal P-3m1 space group. Y(1) is bonded in a 6-coordinate geometry to three equivalent Fe(2), one Si(3), one Si(4), three equivalent Si(1), and three equivalent Si(2) atoms. All Y(1)-Fe(2) bond lengths are 3.21 Å. The Y(1)-Si(3) bond length is 3.12 Å. The Y(1)-Si(4) bond length is 3.20 Å. All Y(1)-Si(1) bond lengths are 2.87 Å. All Y(1)-Si(2) bond lengths are 2.94 Å. There are two inequivalent Fe sites. In the first Fe site, Fe(1) is bonded in a 7-coordinate geometry to three equivalent Si(1), three equivalent Si(5), and four equivalent Si(3) atoms. All Fe(1)-Si(1) bond lengths are 2.47 Å. All Fe(1)-Si(5) bond lengths are 2.69 Å. There are three shorter (2.31 Å) and one longer (2.46 Å) Fe(1)-Si(3) bond length. In the second Fe site, Fe(2) is bonded in a 10-coordinate geometry to three equivalent Y(1), three equivalent Si(2), and four equivalent Si(4) atoms. All Fe(2)-Si(2) bond lengths are 2.31 Å. There is one shorter (2.31 Å) and three longer (2.46 Å) Fe(2)-Si(4) bond lengths. There are five inequivalent Si sites. In the first Si site, Si(1) is bonded in a 10-coordinate geometry to three equivalent Y(1), three equivalent Fe(1), one Si(5), and three equivalent Si(3) atoms. The Si(1)-Si(5) bond length is 2.40 Å. All Si(1)-Si(3) bond lengths are 2.65 Å. In the second Si site, Si(2) is bonded in a 9-coordinate geometry to three equivalent Y(1), three equivalent Fe(2), and three equivalent Si(4) atoms. All Si(2)-Si(4) bond lengths are 2.64 Å. In the third Si site, Si(3) is bonded in a 11-coordinate geometry to one Y(1), four equivalent Fe(1), three equivalent Si(1), and three equivalent Si(5) atoms. All Si(3)-Si(5) bond lengths are 2.50 Å. In the fourth Si site, Si(4) is bonded in a 11-coordinate geometry to one Y(1), four equivalent Fe(2), three equivalent Si(2), and three equivalent Si(4) atoms. All Si(4)-Si(4) bond lengths are 2.66 Å. In the fifth Si site, Si(5) is bonded in a 14-coordinate geometry to six equivalent Fe(1), two equivalent Si(1), and six equivalent Si(3) atoms.