CaY2(FeO2)4 crystallizes in the monoclinic C2/m space group. Ca(1) is bonded to two equivalent O(2) and four equivalent O(1) atoms to form CaO6 octahedra that share corners with four equivalent Y(1)O6 octahedra, corners with six equivalent Fe(2)O6 octahedra, edges with two equivalent Fe(3)O6 octahedra, edges with four equivalent Fe(1)O6 octahedra, and faces with two equivalent Y(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 13-55°. Y(1) is bonded to one O(2), one O(3), and four equivalent O(1) atoms to form distorted YO6 octahedra that share corners with two equivalent Ca(1)O6 octahedra, corners with two equivalent Fe(2)O6 octahedra, corners with two equivalent Fe(3)O6 octahedra, corners with eight equivalent Fe(1)O6 octahedra, edges with two equivalent Y(1)O6 octahedra,  a faceface with one Ca(1)O6 octahedra,  a faceface with one Fe(2)O6 octahedra, and  a faceface with one Fe(3)O6 octahedra. The corner-sharing octahedral tilt angles range from 35-72°. There are three inequivalent Fe sites. In the first Fe site, Fe(1) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(3) atoms to form distorted FeO6 octahedra that share corners with eight equivalent Y(1)O6 octahedra, edges with two equivalent Ca(1)O6 octahedra, edges with two equivalent Fe(1)O6 octahedra, edges with two equivalent Fe(2)O6 octahedra, and edges with two equivalent Fe(3)O6 octahedra. The corner-sharing octahedral tilt angles range from 37-56°. In the second Fe site, Fe(2) is bonded to two equivalent O(2) and four equivalent O(1) atoms to form distorted FeO6 octahedra that share corners with four equivalent Y(1)O6 octahedra, corners with six equivalent Ca(1)O6 octahedra, edges with two equivalent Fe(3)O6 octahedra, edges with four equivalent Fe(1)O6 octahedra, and faces with two equivalent Y(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 13-72°. In the third Fe site, Fe(3) is bonded to two equivalent O(3) and four equivalent O(1) atoms to form FeO6 octahedra that share corners with four equivalent Y(1)O6 octahedra, edges with two equivalent Ca(1)O6 octahedra, edges with two equivalent Fe(2)O6 octahedra, edges with four equivalent Fe(1)O6 octahedra, and faces with two equivalent Y(1)O6 octahedra. The corner-sharing octahedral tilt angles are 35°. There are three inequivalent O sites. In the first O site, O(1) is bonded to one Ca(1), two equivalent Y(1), one Fe(1), one Fe(2), and one Fe(3) atom to form distorted OCaY2Fe3 pentagonal pyramids that share corners with seven equivalent O(1)CaY2Fe3 pentagonal pyramids, corners with two equivalent O(3)YFe3 trigonal pyramids, edges with three equivalent O(1)CaY2Fe3 pentagonal pyramids, edges with four equivalent O(2)CaYFe3 trigonal bipyramids, edges with two equivalent O(3)YFe3 trigonal pyramids, and  a faceface with one O(1)CaY2Fe3 pentagonal pyramid. In the second O site, O(2) is bonded to one Ca(1), one Y(1), one Fe(2), and two equivalent Fe(1) atoms to form distorted OCaYFe3 trigonal bipyramids that share corners with four equivalent O(2)CaYFe3 trigonal bipyramids, corners with three equivalent O(3)YFe3 trigonal pyramids, edges with eight equivalent O(1)CaY2Fe3 pentagonal pyramids, and  an edgeedge with one O(3)YFe3 trigonal pyramid. In the third O site, O(3) is bonded to one Y(1), one Fe(3), and two equivalent Fe(1) atoms to form OYFe3 trigonal pyramids that share corners with four equivalent O(1)CaY2Fe3 pentagonal pyramids, corners with three equivalent O(2)CaYFe3 trigonal bipyramids, corners with three equivalent O(3)YFe3 trigonal pyramids, edges with four equivalent O(1)CaY2Fe3 pentagonal pyramids, and  an edgeedge with one O(2)CaYFe3 trigonal bipyramid.
CaY2(FeO2)4 crystallizes in the monoclinic C2/m space group. Ca(1) is bonded to two equivalent O(2) and four equivalent O(1) atoms to form CaO6 octahedra that share corners with four equivalent Y(1)O6 octahedra, corners with six equivalent Fe(2)O6 octahedra, edges with two equivalent Fe(3)O6 octahedra, edges with four equivalent Fe(1)O6 octahedra, and faces with two equivalent Y(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 13-55°. Both Ca(1)-O(2) bond lengths are 2.27 Å. All Ca(1)-O(1) bond lengths are 2.43 Å. Y(1) is bonded to one O(2), one O(3), and four equivalent O(1) atoms to form distorted YO6 octahedra that share corners with two equivalent Ca(1)O6 octahedra, corners with two equivalent Fe(2)O6 octahedra, corners with two equivalent Fe(3)O6 octahedra, corners with eight equivalent Fe(1)O6 octahedra, edges with two equivalent Y(1)O6 octahedra,  a faceface with one Ca(1)O6 octahedra,  a faceface with one Fe(2)O6 octahedra, and  a faceface with one Fe(3)O6 octahedra. The corner-sharing octahedral tilt angles range from 35-72°. The Y(1)-O(2) bond length is 2.49 Å. The Y(1)-O(3) bond length is 2.19 Å. There are two shorter (2.27 Å) and two longer (2.36 Å) Y(1)-O(1) bond lengths. There are three inequivalent Fe sites. In the first Fe site, Fe(1) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(3) atoms to form distorted FeO6 octahedra that share corners with eight equivalent Y(1)O6 octahedra, edges with two equivalent Ca(1)O6 octahedra, edges with two equivalent Fe(1)O6 octahedra, edges with two equivalent Fe(2)O6 octahedra, and edges with two equivalent Fe(3)O6 octahedra. The corner-sharing octahedral tilt angles range from 37-56°. Both Fe(1)-O(1) bond lengths are 2.58 Å. Both Fe(1)-O(2) bond lengths are 2.29 Å. Both Fe(1)-O(3) bond lengths are 2.00 Å. In the second Fe site, Fe(2) is bonded to two equivalent O(2) and four equivalent O(1) atoms to form distorted FeO6 octahedra that share corners with four equivalent Y(1)O6 octahedra, corners with six equivalent Ca(1)O6 octahedra, edges with two equivalent Fe(3)O6 octahedra, edges with four equivalent Fe(1)O6 octahedra, and faces with two equivalent Y(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 13-72°. Both Fe(2)-O(2) bond lengths are 1.95 Å. All Fe(2)-O(1) bond lengths are 2.58 Å. In the third Fe site, Fe(3) is bonded to two equivalent O(3) and four equivalent O(1) atoms to form FeO6 octahedra that share corners with four equivalent Y(1)O6 octahedra, edges with two equivalent Ca(1)O6 octahedra, edges with two equivalent Fe(2)O6 octahedra, edges with four equivalent Fe(1)O6 octahedra, and faces with two equivalent Y(1)O6 octahedra. The corner-sharing octahedral tilt angles are 35°. Both Fe(3)-O(3) bond lengths are 2.07 Å. All Fe(3)-O(1) bond lengths are 2.30 Å. There are three inequivalent O sites. In the first O site, O(1) is bonded to one Ca(1), two equivalent Y(1), one Fe(1), one Fe(2), and one Fe(3) atom to form distorted OCaY2Fe3 pentagonal pyramids that share corners with seven equivalent O(1)CaY2Fe3 pentagonal pyramids, corners with two equivalent O(3)YFe3 trigonal pyramids, edges with three equivalent O(1)CaY2Fe3 pentagonal pyramids, edges with four equivalent O(2)CaYFe3 trigonal bipyramids, edges with two equivalent O(3)YFe3 trigonal pyramids, and  a faceface with one O(1)CaY2Fe3 pentagonal pyramid. In the second O site, O(2) is bonded to one Ca(1), one Y(1), one Fe(2), and two equivalent Fe(1) atoms to form distorted OCaYFe3 trigonal bipyramids that share corners with four equivalent O(2)CaYFe3 trigonal bipyramids, corners with three equivalent O(3)YFe3 trigonal pyramids, edges with eight equivalent O(1)CaY2Fe3 pentagonal pyramids, and  an edgeedge with one O(3)YFe3 trigonal pyramid. In the third O site, O(3) is bonded to one Y(1), one Fe(3), and two equivalent Fe(1) atoms to form OYFe3 trigonal pyramids that share corners with four equivalent O(1)CaY2Fe3 pentagonal pyramids, corners with three equivalent O(2)CaYFe3 trigonal bipyramids, corners with three equivalent O(3)YFe3 trigonal pyramids, edges with four equivalent O(1)CaY2Fe3 pentagonal pyramids, and  an edgeedge with one O(2)CaYFe3 trigonal bipyramid.