Ca5Hg3 crystallizes in the monoclinic C2/c space group. There are three inequivalent Ca sites. In the first Ca site, Ca(1) is bonded to two equivalent Hg(1) and four equivalent Hg(2) atoms to form distorted CaHg6 octahedra that share corners with six equivalent Ca(1)Hg6 octahedra, corners with eight equivalent Ca(2)Hg5 trigonal bipyramids, corners with eight equivalent Ca(3)Hg5 trigonal bipyramids, faces with four equivalent Ca(2)Hg5 trigonal bipyramids, and faces with four equivalent Ca(3)Hg5 trigonal bipyramids. The corner-sharing octahedral tilt angles range from 0-50°. In the second Ca site, Ca(2) is bonded to two equivalent Hg(1) and three equivalent Hg(2) atoms to form distorted CaHg5 trigonal bipyramids that share corners with four equivalent Ca(1)Hg6 octahedra, corners with four equivalent Ca(2)Hg5 trigonal bipyramids, corners with eight equivalent Ca(3)Hg5 trigonal bipyramids, edges with three equivalent Ca(3)Hg5 trigonal bipyramids, edges with four equivalent Ca(2)Hg5 trigonal bipyramids, faces with two equivalent Ca(1)Hg6 octahedra, and  a faceface with one Ca(3)Hg5 trigonal bipyramid. The corner-sharing octahedral tilt angles range from 43-64°. In the third Ca site, Ca(3) is bonded to two equivalent Hg(1) and three equivalent Hg(2) atoms to form distorted CaHg5 trigonal bipyramids that share corners with four equivalent Ca(1)Hg6 octahedra, corners with four equivalent Ca(3)Hg5 trigonal bipyramids, corners with eight equivalent Ca(2)Hg5 trigonal bipyramids, edges with three equivalent Ca(2)Hg5 trigonal bipyramids, edges with four equivalent Ca(3)Hg5 trigonal bipyramids, faces with two equivalent Ca(1)Hg6 octahedra, and  a faceface with one Ca(2)Hg5 trigonal bipyramid. The corner-sharing octahedral tilt angles range from 43-64°. There are two inequivalent Hg sites. In the first Hg site, Hg(1) is bonded in a 10-coordinate geometry to two equivalent Ca(1), four equivalent Ca(2), and four equivalent Ca(3) atoms. In the second Hg site, Hg(2) is bonded in a 8-coordinate geometry to two equivalent Ca(1), three equivalent Ca(2), and three equivalent Ca(3) atoms.
Ca5Hg3 crystallizes in the monoclinic C2/c space group. There are three inequivalent Ca sites. In the first Ca site, Ca(1) is bonded to two equivalent Hg(1) and four equivalent Hg(2) atoms to form distorted CaHg6 octahedra that share corners with six equivalent Ca(1)Hg6 octahedra, corners with eight equivalent Ca(2)Hg5 trigonal bipyramids, corners with eight equivalent Ca(3)Hg5 trigonal bipyramids, faces with four equivalent Ca(2)Hg5 trigonal bipyramids, and faces with four equivalent Ca(3)Hg5 trigonal bipyramids. The corner-sharing octahedral tilt angles range from 0-50°. Both Ca(1)-Hg(1) bond lengths are 3.64 Å. All Ca(1)-Hg(2) bond lengths are 3.21 Å. In the second Ca site, Ca(2) is bonded to two equivalent Hg(1) and three equivalent Hg(2) atoms to form distorted CaHg5 trigonal bipyramids that share corners with four equivalent Ca(1)Hg6 octahedra, corners with four equivalent Ca(2)Hg5 trigonal bipyramids, corners with eight equivalent Ca(3)Hg5 trigonal bipyramids, edges with three equivalent Ca(3)Hg5 trigonal bipyramids, edges with four equivalent Ca(2)Hg5 trigonal bipyramids, faces with two equivalent Ca(1)Hg6 octahedra, and  a faceface with one Ca(3)Hg5 trigonal bipyramid. The corner-sharing octahedral tilt angles range from 43-64°. There is one shorter (3.42 Å) and one longer (3.43 Å) Ca(2)-Hg(1) bond length. There is one shorter (3.18 Å) and two longer (3.27 Å) Ca(2)-Hg(2) bond lengths. In the third Ca site, Ca(3) is bonded to two equivalent Hg(1) and three equivalent Hg(2) atoms to form distorted CaHg5 trigonal bipyramids that share corners with four equivalent Ca(1)Hg6 octahedra, corners with four equivalent Ca(3)Hg5 trigonal bipyramids, corners with eight equivalent Ca(2)Hg5 trigonal bipyramids, edges with three equivalent Ca(2)Hg5 trigonal bipyramids, edges with four equivalent Ca(3)Hg5 trigonal bipyramids, faces with two equivalent Ca(1)Hg6 octahedra, and  a faceface with one Ca(2)Hg5 trigonal bipyramid. The corner-sharing octahedral tilt angles range from 43-64°. There is one shorter (3.41 Å) and one longer (3.42 Å) Ca(3)-Hg(1) bond length. There are a spread of Ca(3)-Hg(2) bond distances ranging from 3.17-3.27 Å. There are two inequivalent Hg sites. In the first Hg site, Hg(1) is bonded in a 10-coordinate geometry to two equivalent Ca(1), four equivalent Ca(2), and four equivalent Ca(3) atoms. In the second Hg site, Hg(2) is bonded in a 8-coordinate geometry to two equivalent Ca(1), three equivalent Ca(2), and three equivalent Ca(3) atoms.