A series of monoclinic compounds DyCux (x = 4:5; 4 and 3.5) is described. It is constructed from structural blocks AB5 (cubic AuBe5 structure type) and AB2 (cubic MgCu2 structure type) by stacking nAB5 þ AB2 and giving the compositions A2B7;AB4;A4B17;A5B22;A6B27;…;AB5: The resulting monoclinic superstructures can be derived from the cubic AuBe5 type by introducing planar defects parallel to {hhh} that lead to a nearly orthogonal ≈(n + 2)x(n + 2)x(n + 2 - 0:5) supercells. The present series is analogous to the monoclinic–hexagonal–trigonal–orthorhombic series An+1B5n+2 obtained by the stacking (n-1)AB5 þ A2B7 where AB5 is of the hexagonal CaCu5 structure type and A2B7 is of the monoclinic Zr2Ni7 structure type.