Ca4Mg3H14 crystallizes in the hexagonal P-62m space group. There are two inequivalent Ca sites. In the first Ca site, Ca(1) is bonded in a 9-coordinate geometry to three equivalent H(1), three equivalent H(2), and three equivalent H(3) atoms. In the second Ca site, Ca(2) is bonded in a 9-coordinate geometry to three equivalent H(2) and six equivalent H(1) atoms. Mg(1) is bonded in a 5-coordinate geometry to two equivalent H(1), two equivalent H(4), and three equivalent H(3) atoms. There are four inequivalent H sites. In the first H site, H(1) is bonded to one Ca(1), two equivalent Ca(2), and one Mg(1) atom to form distorted HCa3Mg tetrahedra that share corners with three equivalent H(2)Ca4 tetrahedra, corners with eleven equivalent H(1)Ca3Mg tetrahedra, corners with two equivalent H(3)Ca2Mg3 trigonal bipyramids,  an edgeedge with one H(1)Ca3Mg tetrahedra, edges with three equivalent H(2)Ca4 tetrahedra, and edges with two equivalent H(3)Ca2Mg3 trigonal bipyramids. In the second H site, H(2) is bonded to two equivalent Ca(1) and two equivalent Ca(2) atoms to form HCa4 tetrahedra that share corners with four equivalent H(2)Ca4 tetrahedra, corners with six equivalent H(1)Ca3Mg tetrahedra, corners with six equivalent H(3)Ca2Mg3 trigonal bipyramids, edges with two equivalent H(2)Ca4 tetrahedra, and edges with six equivalent H(1)Ca3Mg tetrahedra. In the third H site, H(3) is bonded to two equivalent Ca(1) and three equivalent Mg(1) atoms to form distorted HCa2Mg3 trigonal bipyramids that share corners with four equivalent H(1)Ca3Mg tetrahedra, corners with six equivalent H(2)Ca4 tetrahedra, corners with four equivalent H(3)Ca2Mg3 trigonal bipyramids, edges with four equivalent H(1)Ca3Mg tetrahedra, and faces with two equivalent H(3)Ca2Mg3 trigonal bipyramids. In the fourth H site, H(4) is bonded in a trigonal planar geometry to three equivalent Mg(1) atoms.
Ca4Mg3H14 crystallizes in the hexagonal P-62m space group. There are two inequivalent Ca sites. In the first Ca site, Ca(1) is bonded in a 9-coordinate geometry to three equivalent H(1), three equivalent H(2), and three equivalent H(3) atoms. All Ca(1)-H(1) bond lengths are 2.43 Å. All Ca(1)-H(2) bond lengths are 2.30 Å. All Ca(1)-H(3) bond lengths are 2.31 Å. In the second Ca site, Ca(2) is bonded in a 9-coordinate geometry to three equivalent H(2) and six equivalent H(1) atoms. All Ca(2)-H(2) bond lengths are 2.33 Å. All Ca(2)-H(1) bond lengths are 2.47 Å. Mg(1) is bonded in a 5-coordinate geometry to two equivalent H(1), two equivalent H(4), and three equivalent H(3) atoms. Both Mg(1)-H(1) bond lengths are 1.93 Å. Both Mg(1)-H(4) bond lengths are 1.83 Å. There is one shorter (2.02 Å) and two longer (2.41 Å) Mg(1)-H(3) bond lengths. There are four inequivalent H sites. In the first H site, H(1) is bonded to one Ca(1), two equivalent Ca(2), and one Mg(1) atom to form distorted HCa3Mg tetrahedra that share corners with three equivalent H(2)Ca4 tetrahedra, corners with eleven equivalent H(1)Ca3Mg tetrahedra, corners with two equivalent H(3)Ca2Mg3 trigonal bipyramids,  an edgeedge with one H(1)Ca3Mg tetrahedra, edges with three equivalent H(2)Ca4 tetrahedra, and edges with two equivalent H(3)Ca2Mg3 trigonal bipyramids. In the second H site, H(2) is bonded to two equivalent Ca(1) and two equivalent Ca(2) atoms to form HCa4 tetrahedra that share corners with four equivalent H(2)Ca4 tetrahedra, corners with six equivalent H(1)Ca3Mg tetrahedra, corners with six equivalent H(3)Ca2Mg3 trigonal bipyramids, edges with two equivalent H(2)Ca4 tetrahedra, and edges with six equivalent H(1)Ca3Mg tetrahedra. In the third H site, H(3) is bonded to two equivalent Ca(1) and three equivalent Mg(1) atoms to form distorted HCa2Mg3 trigonal bipyramids that share corners with four equivalent H(1)Ca3Mg tetrahedra, corners with six equivalent H(2)Ca4 tetrahedra, corners with four equivalent H(3)Ca2Mg3 trigonal bipyramids, edges with four equivalent H(1)Ca3Mg tetrahedra, and faces with two equivalent H(3)Ca2Mg3 trigonal bipyramids. In the fourth H site, H(4) is bonded in a trigonal planar geometry to three equivalent Mg(1) atoms.