Mn II-Gd III phosphonate cages with a large magnetocaloric effect are studied. The use of the smallest organophosphonate leads to the formation of the highly symmetric complex, which crystallizes in the hexagonal space group, and the cage has a symmetry. Six of the Gd III centers lie on the nonequatorial edges of the trigonal bipyramid, while the final three Gd III sites form a triangle that lies between the two Mn II triangles. The crystal structure of manganese (II)-gadolinium (III) complex features a distorted [3×3] {Mn 4Gd 6} grid as its core, if a pair of manganese ions is viewed as a node. The two manganese ions of the upper hexagon are only four-coordinate with oxygen atoms from either phosphonates or pivalates, whereas the remaining Mn II ions are six-coordinate.