Ca2Mo3O8 is beta indium sulfide-derived structured and crystallizes in the monoclinic C2/m space group. Ca(1) is bonded to one O(1), one O(2), and four equivalent O(3) atoms to form distorted CaO6 pentagonal pyramids that share corners with three equivalent Mo(1)O6 octahedra, corners with four equivalent Mo(2)O6 octahedra,  an edgeedge with one Mo(1)O6 octahedra, edges with two equivalent Mo(2)O6 octahedra, and edges with two equivalent Ca(1)O6 pentagonal pyramids. The corner-sharing octahedral tilt angles range from 5-53°. There are two inequivalent Mo sites. In the first Mo site, Mo(1) is bonded to two equivalent O(2) and four equivalent O(3) atoms to form MoO6 octahedra that share corners with six equivalent Ca(1)O6 pentagonal pyramids, edges with four equivalent Mo(2)O6 octahedra, and edges with two equivalent Ca(1)O6 pentagonal pyramids. In the second Mo site, Mo(2) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(3) atoms to form MoO6 octahedra that share corners with four equivalent Ca(1)O6 pentagonal pyramids, edges with two equivalent Mo(1)O6 octahedra, edges with two equivalent Mo(2)O6 octahedra, and edges with two equivalent Ca(1)O6 pentagonal pyramids. There are three inequivalent O sites. In the first O site, O(1) is bonded in a trigonal planar geometry to one Ca(1) and two equivalent Mo(2) atoms. In the second O site, O(2) is bonded in a rectangular see-saw-like geometry to one Ca(1), one Mo(1), and two equivalent Mo(2) atoms. In the third O site, O(3) is bonded to two equivalent Ca(1), one Mo(1), and one Mo(2) atom to form a mixture of distorted corner and edge-sharing OCa2Mo2 trigonal pyramids.
Ca2Mo3O8 is beta indium sulfide-derived structured and crystallizes in the monoclinic C2/m space group. Ca(1) is bonded to one O(1), one O(2), and four equivalent O(3) atoms to form distorted CaO6 pentagonal pyramids that share corners with three equivalent Mo(1)O6 octahedra, corners with four equivalent Mo(2)O6 octahedra,  an edgeedge with one Mo(1)O6 octahedra, edges with two equivalent Mo(2)O6 octahedra, and edges with two equivalent Ca(1)O6 pentagonal pyramids. The corner-sharing octahedral tilt angles range from 5-53°. The Ca(1)-O(1) bond length is 2.22 Å. The Ca(1)-O(2) bond length is 2.34 Å. There are two shorter (2.28 Å) and two longer (2.42 Å) Ca(1)-O(3) bond lengths. There are two inequivalent Mo sites. In the first Mo site, Mo(1) is bonded to two equivalent O(2) and four equivalent O(3) atoms to form MoO6 octahedra that share corners with six equivalent Ca(1)O6 pentagonal pyramids, edges with four equivalent Mo(2)O6 octahedra, and edges with two equivalent Ca(1)O6 pentagonal pyramids. Both Mo(1)-O(2) bond lengths are 2.12 Å. All Mo(1)-O(3) bond lengths are 2.02 Å. In the second Mo site, Mo(2) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(3) atoms to form MoO6 octahedra that share corners with four equivalent Ca(1)O6 pentagonal pyramids, edges with two equivalent Mo(1)O6 octahedra, edges with two equivalent Mo(2)O6 octahedra, and edges with two equivalent Ca(1)O6 pentagonal pyramids. Both Mo(2)-O(1) bond lengths are 2.00 Å. Both Mo(2)-O(2) bond lengths are 2.10 Å. Both Mo(2)-O(3) bond lengths are 2.01 Å. There are three inequivalent O sites. In the first O site, O(1) is bonded in a trigonal planar geometry to one Ca(1) and two equivalent Mo(2) atoms. In the second O site, O(2) is bonded in a rectangular see-saw-like geometry to one Ca(1), one Mo(1), and two equivalent Mo(2) atoms. In the third O site, O(3) is bonded to two equivalent Ca(1), one Mo(1), and one Mo(2) atom to form a mixture of distorted corner and edge-sharing OCa2Mo2 trigonal pyramids.