BaMgLa(CoO3)2 crystallizes in the monoclinic Cm space group. Ba(1) is bonded in a 8-coordinate geometry to four equivalent O(1) and four equivalent O(2) atoms. Mg(1) is bonded to one O(1) and four equivalent O(3) atoms to form distorted MgO5 trigonal bipyramids that share  a cornercorner with one Co(1)O6 octahedra, corners with four equivalent Mg(1)O5 trigonal bipyramids, and edges with four equivalent Co(2)O5 trigonal bipyramids. The corner-sharing octahedra are not tilted. La(1) is bonded in a 8-coordinate geometry to four equivalent O(2) and four equivalent O(4) atoms. There are two inequivalent Co sites. In the first Co site, Co(1) is bonded to one O(1), one O(4), and four equivalent O(2) atoms to form CoO6 octahedra that share corners with four equivalent Co(1)O6 octahedra,  a cornercorner with one Mg(1)O5 trigonal bipyramid, and  a cornercorner with one Co(2)O5 trigonal bipyramid. The corner-sharing octahedral tilt angles are 13°. In the second Co site, Co(2) is bonded to one O(4) and four equivalent O(3) atoms to form distorted CoO5 trigonal bipyramids that share  a cornercorner with one Co(1)O6 octahedra, corners with four equivalent Co(2)O5 trigonal bipyramids, and edges with four equivalent Mg(1)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles are 1°. There are four inequivalent O sites. In the first O site, O(1) is bonded to four equivalent Ba(1), one Mg(1), and one Co(1) atom to form distorted OBa4MgCo octahedra that share corners with four equivalent O(1)Ba4MgCo octahedra, corners with four equivalent O(3)Mg2Co2 trigonal pyramids, and edges with four equivalent O(1)Ba4MgCo octahedra. The corner-sharing octahedral tilt angles are 9°. In the second O site, O(2) is bonded in a 6-coordinate geometry to two equivalent Ba(1), two equivalent La(1), and two equivalent Co(1) atoms. In the third O site, O(3) is bonded to two equivalent Mg(1) and two equivalent Co(2) atoms to form distorted OMg2Co2 trigonal pyramids that share corners with two equivalent O(1)Ba4MgCo octahedra, corners with four equivalent O(3)Mg2Co2 trigonal pyramids, and edges with four equivalent O(3)Mg2Co2 trigonal pyramids. The corner-sharing octahedral tilt angles range from 71-72°. In the fourth O site, O(4) is bonded in a 6-coordinate geometry to four equivalent La(1), one Co(1), and one Co(2) atom.
BaMgLa(CoO3)2 crystallizes in the monoclinic Cm space group. Ba(1) is bonded in a 8-coordinate geometry to four equivalent O(1) and four equivalent O(2) atoms. There is one shorter (2.76 Å) and three longer (2.77 Å) Ba(1)-O(1) bond lengths. There are two shorter (2.88 Å) and two longer (2.90 Å) Ba(1)-O(2) bond lengths. Mg(1) is bonded to one O(1) and four equivalent O(3) atoms to form distorted MgO5 trigonal bipyramids that share  a cornercorner with one Co(1)O6 octahedra, corners with four equivalent Mg(1)O5 trigonal bipyramids, and edges with four equivalent Co(2)O5 trigonal bipyramids. The corner-sharing octahedra are not tilted. The Mg(1)-O(1) bond length is 2.01 Å. All Mg(1)-O(3) bond lengths are 2.06 Å. La(1) is bonded in a 8-coordinate geometry to four equivalent O(2) and four equivalent O(4) atoms. There are two shorter (2.49 Å) and two longer (2.52 Å) La(1)-O(2) bond lengths. There are a spread of La(1)-O(4) bond distances ranging from 2.68-2.89 Å. There are two inequivalent Co sites. In the first Co site, Co(1) is bonded to one O(1), one O(4), and four equivalent O(2) atoms to form CoO6 octahedra that share corners with four equivalent Co(1)O6 octahedra,  a cornercorner with one Mg(1)O5 trigonal bipyramid, and  a cornercorner with one Co(2)O5 trigonal bipyramid. The corner-sharing octahedral tilt angles are 13°. The Co(1)-O(1) bond length is 2.13 Å. The Co(1)-O(4) bond length is 2.21 Å. There are two shorter (1.96 Å) and two longer (1.97 Å) Co(1)-O(2) bond lengths. In the second Co site, Co(2) is bonded to one O(4) and four equivalent O(3) atoms to form distorted CoO5 trigonal bipyramids that share  a cornercorner with one Co(1)O6 octahedra, corners with four equivalent Co(2)O5 trigonal bipyramids, and edges with four equivalent Mg(1)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles are 1°. The Co(2)-O(4) bond length is 1.98 Å. There are two shorter (2.01 Å) and two longer (2.03 Å) Co(2)-O(3) bond lengths. There are four inequivalent O sites. In the first O site, O(1) is bonded to four equivalent Ba(1), one Mg(1), and one Co(1) atom to form distorted OBa4MgCo octahedra that share corners with four equivalent O(1)Ba4MgCo octahedra, corners with four equivalent O(3)Mg2Co2 trigonal pyramids, and edges with four equivalent O(1)Ba4MgCo octahedra. The corner-sharing octahedral tilt angles are 9°. In the second O site, O(2) is bonded in a 6-coordinate geometry to two equivalent Ba(1), two equivalent La(1), and two equivalent Co(1) atoms. In the third O site, O(3) is bonded to two equivalent Mg(1) and two equivalent Co(2) atoms to form distorted OMg2Co2 trigonal pyramids that share corners with two equivalent O(1)Ba4MgCo octahedra, corners with four equivalent O(3)Mg2Co2 trigonal pyramids, and edges with four equivalent O(3)Mg2Co2 trigonal pyramids. The corner-sharing octahedral tilt angles range from 71-72°. In the fourth O site, O(4) is bonded in a 6-coordinate geometry to four equivalent La(1), one Co(1), and one Co(2) atom.