K2Mg(CuO2)2 crystallizes in the monoclinic C2/m space group. K(1) is bonded to three equivalent O(1) and three equivalent O(2) atoms to form distorted edge-sharing KO6 pentagonal pyramids. Mg(1) is bonded in a distorted square co-planar geometry to four equivalent O(1) atoms. Cu(1) is bonded in a distorted T-shaped geometry to one O(1) and two equivalent O(2) atoms. There are two inequivalent O sites. In the first O site, O(1) is bonded to three equivalent K(1), two equivalent Mg(1), and one Cu(1) atom to form distorted OK3Mg2Cu octahedra that share corners with two equivalent O(1)K3Mg2Cu octahedra, corners with eight equivalent O(2)K3Cu2 trigonal bipyramids, edges with five equivalent O(1)K3Mg2Cu octahedra, and  a faceface with one O(2)K3Cu2 trigonal bipyramid. The corner-sharing octahedra are not tilted. In the second O site, O(2) is bonded to three equivalent K(1) and two equivalent Cu(1) atoms to form distorted OK3Cu2 trigonal bipyramids that share corners with eight equivalent O(1)K3Mg2Cu octahedra, corners with two equivalent O(2)K3Cu2 trigonal bipyramids, edges with three equivalent O(2)K3Cu2 trigonal bipyramids, and  a faceface with one O(1)K3Mg2Cu octahedra. The corner-sharing octahedral tilt angles range from 22-89°.
K2Mg(CuO2)2 crystallizes in the monoclinic C2/m space group. K(1) is bonded to three equivalent O(1) and three equivalent O(2) atoms to form distorted edge-sharing KO6 pentagonal pyramids. There are two shorter (2.84 Å) and one longer (2.88 Å) K(1)-O(1) bond length. There are two shorter (2.67 Å) and one longer (2.74 Å) K(1)-O(2) bond length. Mg(1) is bonded in a distorted square co-planar geometry to four equivalent O(1) atoms. All Mg(1)-O(1) bond lengths are 2.12 Å. Cu(1) is bonded in a distorted T-shaped geometry to one O(1) and two equivalent O(2) atoms. The Cu(1)-O(1) bond length is 1.88 Å. There is one shorter (1.80 Å) and one longer (1.95 Å) Cu(1)-O(2) bond length. There are two inequivalent O sites. In the first O site, O(1) is bonded to three equivalent K(1), two equivalent Mg(1), and one Cu(1) atom to form distorted OK3Mg2Cu octahedra that share corners with two equivalent O(1)K3Mg2Cu octahedra, corners with eight equivalent O(2)K3Cu2 trigonal bipyramids, edges with five equivalent O(1)K3Mg2Cu octahedra, and  a faceface with one O(2)K3Cu2 trigonal bipyramid. The corner-sharing octahedra are not tilted. In the second O site, O(2) is bonded to three equivalent K(1) and two equivalent Cu(1) atoms to form distorted OK3Cu2 trigonal bipyramids that share corners with eight equivalent O(1)K3Mg2Cu octahedra, corners with two equivalent O(2)K3Cu2 trigonal bipyramids, edges with three equivalent O(2)K3Cu2 trigonal bipyramids, and  a faceface with one O(1)K3Mg2Cu octahedra. The corner-sharing octahedral tilt angles range from 22-89°.