SrMgFe2(SeO3)4 crystallizes in the monoclinic Pm space group. Sr(1) is bonded in a distorted body-centered cubic geometry to two equivalent O(1), two equivalent O(3), two equivalent O(6), and two equivalent O(8) atoms. Mg(1) is bonded in a 4-coordinate geometry to two equivalent O(1) and two equivalent O(3) atoms. There are two inequivalent Fe sites. In the first Fe site, Fe(1) is bonded in an octahedral geometry to one O(4), one O(7), two equivalent O(3), and two equivalent O(6) atoms. In the second Fe site, Fe(2) is bonded in an octahedral geometry to one O(2), one O(5), two equivalent O(1), and two equivalent O(8) atoms. There are four inequivalent Se sites. In the first Se site, Se(1) is bonded in a trigonal non-coplanar geometry to one O(5) and two equivalent O(6) atoms. In the second Se site, Se(2) is bonded in a distorted trigonal non-coplanar geometry to one O(4) and two equivalent O(8) atoms. In the third Se site, Se(3) is bonded in a trigonal non-coplanar geometry to one O(7) and two equivalent O(1) atoms. In the fourth Se site, Se(4) is bonded in a trigonal non-coplanar geometry to one O(2) and two equivalent O(3) atoms. There are eight inequivalent O sites. In the first O site, O(1) is bonded to one Sr(1), one Mg(1), one Fe(2), and one Se(3) atom to form distorted edge-sharing OSrMgFeSe tetrahedra. In the second O site, O(2) is bonded in a bent 150 degrees geometry to one Fe(2) and one Se(4) atom. In the third O site, O(3) is bonded in a 4-coordinate geometry to one Sr(1), one Mg(1), one Fe(1), and one Se(4) atom. In the fourth O site, O(4) is bonded in a bent 150 degrees geometry to one Fe(1) and one Se(2) atom. In the fifth O site, O(5) is bonded in a bent 120 degrees geometry to one Fe(2) and one Se(1) atom. In the sixth O site, O(6) is bonded in a 3-coordinate geometry to one Sr(1), one Fe(1), and one Se(1) atom. In the seventh O site, O(7) is bonded in a bent 150 degrees geometry to one Fe(1) and one Se(3) atom. In the eighth O site, O(8) is bonded in a 3-coordinate geometry to one Sr(1), one Fe(2), and one Se(2) atom.
SrMgFe2(SeO3)4 crystallizes in the monoclinic Pm space group. Sr(1) is bonded in a distorted body-centered cubic geometry to two equivalent O(1), two equivalent O(3), two equivalent O(6), and two equivalent O(8) atoms. Both Sr(1)-O(1) bond lengths are 2.77 Å. Both Sr(1)-O(3) bond lengths are 2.89 Å. Both Sr(1)-O(6) bond lengths are 2.59 Å. Both Sr(1)-O(8) bond lengths are 2.55 Å. Mg(1) is bonded in a 4-coordinate geometry to two equivalent O(1) and two equivalent O(3) atoms. Both Mg(1)-O(1) bond lengths are 2.08 Å. Both Mg(1)-O(3) bond lengths are 2.02 Å. There are two inequivalent Fe sites. In the first Fe site, Fe(1) is bonded in an octahedral geometry to one O(4), one O(7), two equivalent O(3), and two equivalent O(6) atoms. The Fe(1)-O(4) bond length is 2.09 Å. The Fe(1)-O(7) bond length is 2.15 Å. Both Fe(1)-O(3) bond lengths are 2.36 Å. Both Fe(1)-O(6) bond lengths are 2.05 Å. In the second Fe site, Fe(2) is bonded in an octahedral geometry to one O(2), one O(5), two equivalent O(1), and two equivalent O(8) atoms. The Fe(2)-O(2) bond length is 2.12 Å. The Fe(2)-O(5) bond length is 2.05 Å. Both Fe(2)-O(1) bond lengths are 2.29 Å. Both Fe(2)-O(8) bond lengths are 2.18 Å. There are four inequivalent Se sites. In the first Se site, Se(1) is bonded in a trigonal non-coplanar geometry to one O(5) and two equivalent O(6) atoms. The Se(1)-O(5) bond length is 1.72 Å. Both Se(1)-O(6) bond lengths are 1.75 Å. In the second Se site, Se(2) is bonded in a distorted trigonal non-coplanar geometry to one O(4) and two equivalent O(8) atoms. The Se(2)-O(4) bond length is 1.69 Å. Both Se(2)-O(8) bond lengths are 1.73 Å. In the third Se site, Se(3) is bonded in a trigonal non-coplanar geometry to one O(7) and two equivalent O(1) atoms. The Se(3)-O(7) bond length is 1.68 Å. Both Se(3)-O(1) bond lengths are 1.79 Å. In the fourth Se site, Se(4) is bonded in a trigonal non-coplanar geometry to one O(2) and two equivalent O(3) atoms. The Se(4)-O(2) bond length is 1.69 Å. Both Se(4)-O(3) bond lengths are 1.78 Å. There are eight inequivalent O sites. In the first O site, O(1) is bonded to one Sr(1), one Mg(1), one Fe(2), and one Se(3) atom to form distorted edge-sharing OSrMgFeSe tetrahedra. In the second O site, O(2) is bonded in a bent 150 degrees geometry to one Fe(2) and one Se(4) atom. In the third O site, O(3) is bonded in a 4-coordinate geometry to one Sr(1), one Mg(1), one Fe(1), and one Se(4) atom. In the fourth O site, O(4) is bonded in a bent 150 degrees geometry to one Fe(1) and one Se(2) atom. In the fifth O site, O(5) is bonded in a bent 120 degrees geometry to one Fe(2) and one Se(1) atom. In the sixth O site, O(6) is bonded in a 3-coordinate geometry to one Sr(1), one Fe(1), and one Se(1) atom. In the seventh O site, O(7) is bonded in a bent 150 degrees geometry to one Fe(1) and one Se(3) atom. In the eighth O site, O(8) is bonded in a 3-coordinate geometry to one Sr(1), one Fe(2), and one Se(2) atom.