Ca9(FeN4)2 crystallizes in the monoclinic C2/m space group. There are five inequivalent Ca sites. In the first Ca site, Ca(1) is bonded in a linear geometry to two equivalent N(4) atoms. In the second Ca site, Ca(2) is bonded to one N(2), two equivalent N(1), and two equivalent N(4) atoms to form a mixture of distorted corner and edge-sharing CaN5 square pyramids. In the third Ca site, Ca(3) is bonded to one N(3), one N(4), and three equivalent N(2) atoms to form a mixture of distorted corner and edge-sharing CaN5 trigonal bipyramids. In the fourth Ca site, Ca(4) is bonded in a 5-coordinate geometry to one N(3), two equivalent N(1), and two equivalent N(4) atoms. In the fifth Ca site, Ca(5) is bonded in a 5-coordinate geometry to one N(1), one N(2), and three equivalent N(3) atoms. Fe(1) is bonded in a trigonal planar geometry to one N(1), one N(2), and one N(3) atom. There are four inequivalent N sites. In the first N site, N(1) is bonded to one Ca(5), two equivalent Ca(2), two equivalent Ca(4), and one Fe(1) atom to form distorted NCa5Fe octahedra that share corners with two equivalent N(1)Ca5Fe octahedra,  an edgeedge with one N(1)Ca5Fe octahedra, and edges with four equivalent N(4)Ca6 octahedra. The corner-sharing octahedral tilt angles are 17°. In the second N site, N(2) is bonded in a 5-coordinate geometry to one Ca(2), one Ca(5), three equivalent Ca(3), and one Fe(1) atom. In the third N site, N(3) is bonded in a 6-coordinate geometry to one Ca(3), one Ca(4), three equivalent Ca(5), and one Fe(1) atom. In the fourth N site, N(4) is bonded to one Ca(1), one Ca(3), two equivalent Ca(2), and two equivalent Ca(4) atoms to form NCa6 octahedra that share corners with three equivalent N(4)Ca6 octahedra,  an edgeedge with one N(4)Ca6 octahedra, and edges with four equivalent N(1)Ca5Fe octahedra. The corner-sharing octahedral tilt angles range from 0-5°.
Ca9(FeN4)2 crystallizes in the monoclinic C2/m space group. There are five inequivalent Ca sites. In the first Ca site, Ca(1) is bonded in a linear geometry to two equivalent N(4) atoms. Both Ca(1)-N(4) bond lengths are 2.31 Å. In the second Ca site, Ca(2) is bonded to one N(2), two equivalent N(1), and two equivalent N(4) atoms to form a mixture of distorted corner and edge-sharing CaN5 square pyramids. The Ca(2)-N(2) bond length is 2.51 Å. There is one shorter (2.61 Å) and one longer (2.67 Å) Ca(2)-N(1) bond length. Both Ca(2)-N(4) bond lengths are 2.47 Å. In the third Ca site, Ca(3) is bonded to one N(3), one N(4), and three equivalent N(2) atoms to form a mixture of distorted corner and edge-sharing CaN5 trigonal bipyramids. The Ca(3)-N(3) bond length is 2.65 Å. The Ca(3)-N(4) bond length is 2.44 Å. All Ca(3)-N(2) bond lengths are 2.50 Å. In the fourth Ca site, Ca(4) is bonded in a 5-coordinate geometry to one N(3), two equivalent N(1), and two equivalent N(4) atoms. The Ca(4)-N(3) bond length is 3.08 Å. Both Ca(4)-N(1) bond lengths are 2.49 Å. There is one shorter (2.35 Å) and one longer (2.56 Å) Ca(4)-N(4) bond length. In the fifth Ca site, Ca(5) is bonded in a 5-coordinate geometry to one N(1), one N(2), and three equivalent N(3) atoms. The Ca(5)-N(1) bond length is 2.47 Å. The Ca(5)-N(2) bond length is 3.13 Å. There are two shorter (2.49 Å) and one longer (2.78 Å) Ca(5)-N(3) bond length. Fe(1) is bonded in a trigonal planar geometry to one N(1), one N(2), and one N(3) atom. The Fe(1)-N(1) bond length is 1.75 Å. The Fe(1)-N(2) bond length is 1.73 Å. The Fe(1)-N(3) bond length is 1.75 Å. There are four inequivalent N sites. In the first N site, N(1) is bonded to one Ca(5), two equivalent Ca(2), two equivalent Ca(4), and one Fe(1) atom to form distorted NCa5Fe octahedra that share corners with two equivalent N(1)Ca5Fe octahedra,  an edgeedge with one N(1)Ca5Fe octahedra, and edges with four equivalent N(4)Ca6 octahedra. The corner-sharing octahedral tilt angles are 17°. In the second N site, N(2) is bonded in a 5-coordinate geometry to one Ca(2), one Ca(5), three equivalent Ca(3), and one Fe(1) atom. In the third N site, N(3) is bonded in a 6-coordinate geometry to one Ca(3), one Ca(4), three equivalent Ca(5), and one Fe(1) atom. In the fourth N site, N(4) is bonded to one Ca(1), one Ca(3), two equivalent Ca(2), and two equivalent Ca(4) atoms to form NCa6 octahedra that share corners with three equivalent N(4)Ca6 octahedra,  an edgeedge with one N(4)Ca6 octahedra, and edges with four equivalent N(1)Ca5Fe octahedra. The corner-sharing octahedral tilt angles range from 0-5°.