Mg7As6(HO6)4 crystallizes in the triclinic P-1 space group. There are four inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to two equivalent O(12), two equivalent O(2), and two equivalent O(7) atoms to form MgO6 octahedra that share corners with two equivalent Mg(2)O6 octahedra, corners with two equivalent As(1)O4 tetrahedra, corners with two equivalent As(2)O4 tetrahedra, and corners with two equivalent Mg(3)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles are 57°. In the second Mg site, Mg(2) is bonded to one O(10), one O(2), one O(3), one O(8), and two equivalent O(5) atoms to form distorted MgO6 octahedra that share  a cornercorner with one Mg(1)O6 octahedra, corners with two equivalent As(1)O4 tetrahedra, corners with three equivalent As(2)O4 tetrahedra,  an edgeedge with one Mg(2)O6 octahedra, and  an edgeedge with one Mg(3)O5 trigonal bipyramid. The corner-sharing octahedral tilt angles are 57°. In the third Mg site, Mg(3) is bonded to one O(1), one O(12), one O(3), one O(8), and one O(9) atom to form distorted MgO5 trigonal bipyramids that share  a cornercorner with one Mg(1)O6 octahedra,  a cornercorner with one As(2)O4 tetrahedra, corners with two equivalent As(1)O4 tetrahedra, and  an edgeedge with one Mg(2)O6 octahedra. The corner-sharing octahedral tilt angles are 60°. In the fourth Mg site, Mg(4) is bonded in a 6-coordinate geometry to one O(1), one O(10), one O(11), one O(9), and two equivalent O(6) atoms. There are three inequivalent As sites. In the first As site, As(1) is bonded to one O(1), one O(2), one O(3), and one O(4) atom to form AsO4 tetrahedra that share  a cornercorner with one Mg(1)O6 octahedra, corners with two equivalent Mg(2)O6 octahedra, and corners with two equivalent Mg(3)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles range from 57-70°. In the second As site, As(2) is bonded to one O(5), one O(6), one O(7), and one O(8) atom to form AsO4 tetrahedra that share  a cornercorner with one Mg(1)O6 octahedra, corners with three equivalent Mg(2)O6 octahedra, and  a cornercorner with one Mg(3)O5 trigonal bipyramid. The corner-sharing octahedral tilt angles range from 25-55°. In the third As site, As(3) is bonded in a distorted trigonal non-coplanar geometry to one O(10), one O(12), and one O(9) atom. There are two inequivalent H sites. In the first H site, H(1) is bonded in a linear geometry to one O(11) and one O(7) atom. In the second H site, H(2) is bonded in a single-bond geometry to one O(10) atom. There are twelve inequivalent O sites. In the first O site, O(1) is bonded in a distorted trigonal planar geometry to one Mg(3), one Mg(4), and one As(1) atom. In the second O site, O(2) is bonded in a trigonal planar geometry to one Mg(1), one Mg(2), and one As(1) atom. In the third O site, O(3) is bonded in a trigonal planar geometry to one Mg(2), one Mg(3), and one As(1) atom. In the fourth O site, O(4) is bonded in a distorted water-like geometry to one As(1) and one O(11) atom. In the fifth O site, O(5) is bonded in a distorted trigonal planar geometry to two equivalent Mg(2) and one As(2) atom. In the sixth O site, O(6) is bonded in a trigonal planar geometry to two equivalent Mg(4) and one As(2) atom. In the seventh O site, O(7) is bonded in a distorted T-shaped geometry to one Mg(1), one As(2), and one H(1) atom. In the eighth O site, O(8) is bonded in a trigonal planar geometry to one Mg(2), one Mg(3), and one As(2) atom. In the ninth O site, O(9) is bonded in a distorted trigonal non-coplanar geometry to one Mg(3), one Mg(4), and one As(3) atom. In the tenth O site, O(10) is bonded in a distorted single-bond geometry to one Mg(2), one Mg(4), one As(3), and one H(2) atom. In the eleventh O site, O(11) is bonded in a distorted single-bond geometry to one Mg(4), one H(1), and one O(4) atom. In the twelfth O site, O(12) is bonded in a trigonal planar geometry to one Mg(1), one Mg(3), and one As(3) atom.
Mg7As6(HO6)4 crystallizes in the triclinic P-1 space group. There are four inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to two equivalent O(12), two equivalent O(2), and two equivalent O(7) atoms to form MgO6 octahedra that share corners with two equivalent Mg(2)O6 octahedra, corners with two equivalent As(1)O4 tetrahedra, corners with two equivalent As(2)O4 tetrahedra, and corners with two equivalent Mg(3)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles are 57°. Both Mg(1)-O(12) bond lengths are 2.16 Å. Both Mg(1)-O(2) bond lengths are 2.44 Å. Both Mg(1)-O(7) bond lengths are 2.17 Å. In the second Mg site, Mg(2) is bonded to one O(10), one O(2), one O(3), one O(8), and two equivalent O(5) atoms to form distorted MgO6 octahedra that share  a cornercorner with one Mg(1)O6 octahedra, corners with two equivalent As(1)O4 tetrahedra, corners with three equivalent As(2)O4 tetrahedra,  an edgeedge with one Mg(2)O6 octahedra, and  an edgeedge with one Mg(3)O5 trigonal bipyramid. The corner-sharing octahedral tilt angles are 57°. The Mg(2)-O(10) bond length is 2.11 Å. The Mg(2)-O(2) bond length is 2.19 Å. The Mg(2)-O(3) bond length is 2.07 Å. The Mg(2)-O(8) bond length is 2.08 Å. There is one shorter (2.07 Å) and one longer (2.17 Å) Mg(2)-O(5) bond length. In the third Mg site, Mg(3) is bonded to one O(1), one O(12), one O(3), one O(8), and one O(9) atom to form distorted MgO5 trigonal bipyramids that share  a cornercorner with one Mg(1)O6 octahedra,  a cornercorner with one As(2)O4 tetrahedra, corners with two equivalent As(1)O4 tetrahedra, and  an edgeedge with one Mg(2)O6 octahedra. The corner-sharing octahedral tilt angles are 60°. The Mg(3)-O(1) bond length is 2.20 Å. The Mg(3)-O(12) bond length is 2.04 Å. The Mg(3)-O(3) bond length is 2.13 Å. The Mg(3)-O(8) bond length is 2.12 Å. The Mg(3)-O(9) bond length is 2.00 Å. In the fourth Mg site, Mg(4) is bonded in a 6-coordinate geometry to one O(1), one O(10), one O(11), one O(9), and two equivalent O(6) atoms. The Mg(4)-O(1) bond length is 2.09 Å. The Mg(4)-O(10) bond length is 2.58 Å. The Mg(4)-O(11) bond length is 2.08 Å. The Mg(4)-O(9) bond length is 2.06 Å. There is one shorter (2.05 Å) and one longer (2.12 Å) Mg(4)-O(6) bond length. There are three inequivalent As sites. In the first As site, As(1) is bonded to one O(1), one O(2), one O(3), and one O(4) atom to form AsO4 tetrahedra that share  a cornercorner with one Mg(1)O6 octahedra, corners with two equivalent Mg(2)O6 octahedra, and corners with two equivalent Mg(3)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles range from 57-70°. The As(1)-O(1) bond length is 1.70 Å. The As(1)-O(2) bond length is 1.72 Å. The As(1)-O(3) bond length is 1.71 Å. The As(1)-O(4) bond length is 1.81 Å. In the second As site, As(2) is bonded to one O(5), one O(6), one O(7), and one O(8) atom to form AsO4 tetrahedra that share  a cornercorner with one Mg(1)O6 octahedra, corners with three equivalent Mg(2)O6 octahedra, and  a cornercorner with one Mg(3)O5 trigonal bipyramid. The corner-sharing octahedral tilt angles range from 25-55°. The As(2)-O(5) bond length is 1.72 Å. The As(2)-O(6) bond length is 1.73 Å. The As(2)-O(7) bond length is 1.73 Å. The As(2)-O(8) bond length is 1.72 Å. In the third As site, As(3) is bonded in a distorted trigonal non-coplanar geometry to one O(10), one O(12), and one O(9) atom. The As(3)-O(10) bond length is 1.95 Å. The As(3)-O(12) bond length is 1.80 Å. The As(3)-O(9) bond length is 1.76 Å. There are two inequivalent H sites. In the first H site, H(1) is bonded in a linear geometry to one O(11) and one O(7) atom. The H(1)-O(11) bond length is 1.05 Å. The H(1)-O(7) bond length is 1.47 Å. In the second H site, H(2) is bonded in a single-bond geometry to one O(10) atom. The H(2)-O(10) bond length is 0.99 Å. There are twelve inequivalent O sites. In the first O site, O(1) is bonded in a distorted trigonal planar geometry to one Mg(3), one Mg(4), and one As(1) atom. In the second O site, O(2) is bonded in a trigonal planar geometry to one Mg(1), one Mg(2), and one As(1) atom. In the third O site, O(3) is bonded in a trigonal planar geometry to one Mg(2), one Mg(3), and one As(1) atom. In the fourth O site, O(4) is bonded in a distorted water-like geometry to one As(1) and one O(11) atom. The O(4)-O(11) bond length is 1.47 Å. In the fifth O site, O(5) is bonded in a distorted trigonal planar geometry to two equivalent Mg(2) and one As(2) atom. In the sixth O site, O(6) is bonded in a trigonal planar geometry to two equivalent Mg(4) and one As(2) atom. In the seventh O site, O(7) is bonded in a distorted T-shaped geometry to one Mg(1), one As(2), and one H(1) atom. In the eighth O site, O(8) is bonded in a trigonal planar geometry to one Mg(2), one Mg(3), and one As(2) atom. In the ninth O site, O(9) is bonded in a distorted trigonal non-coplanar geometry to one Mg(3), one Mg(4), and one As(3) atom. In the tenth O site, O(10) is bonded in a distorted single-bond geometry to one Mg(2), one Mg(4), one As(3), and one H(2) atom. In the eleventh O site, O(11) is bonded in a distorted single-bond geometry to one Mg(4), one H(1), and one O(4) atom. In the twelfth O site, O(12) is bonded in a trigonal planar geometry to one Mg(1), one Mg(3), and one As(3) atom.