Single crystals of Lu(ClO 4 ) 3 ´3 H 2 O were obtained by slow dehydration of Lu(ClO 4 ) 3 ´6 H 2 O at 140 °C under flowing argon. The compound crystallizes in the triclinic crystal system (P1, Z = 2, a = 750.3(1), b = 838.4(1), c = 1054.6(2) pm, a = 79.77(2)°, b = 79.18(2), c = 63.83(2), R all = 0.0426) with Lu 3+ eightfold coordinated by oxygen atoms, which belong to five ClO 4 ± groups and three H 2 O molecules. The [LuO 8 ] polyhedra and ClO 4 ± groups are connected to form chains which are held together only via hydrogen bridges. Er(ClO 4 ) 3 ´H2 O can also be prepared by dehydration of the respective hexahydrate but only at higher temperature and under vacuum. The triclinic compound (P1, Z = 2, a = 678.31(9), b = 783.4(1), c = 955.9(1) pm, a = 77.29(1)°, b = 75.71(1)°, c = 78.31(1)°, R all = 0.0292) contains Er 3+ ions which are coordinated by seven ClO 4 ± groups and one H 2 O molecule. The linkage of the [ErO 8 ] polyhedra and ClO 4
± tetrahedra results in a three-dimensional network. Attempts to dehydrate Sc(ClO 4 ) 3 ´6 H 2 O led to the basic perchlorate Sc(OH)(ClO 4 ) 2 ´H2 O. In the monoclinic structure (P2 1 /n, Z = 4, a = 942.8(1), b = 735.16(8), c = 1157.9(2) pm, b = 93.76(2)°, R all = 0.0579), Sc 3+ is surrounded by six oxygen atoms which belong to three ClO 4 ± ions, two OH ± groups and one H 2 O molecule. These octahedra are connected via common edges which are formed by the OH ± groups to pairs according to [Sc 2 (OH) 2 (ClO 4 ) 6 (H 2 O) 2 ] 2± . Four of the six ClO 4 ± groups link the pairs to two-dimensional infinite sheets, which are held together via hydrogen bonds.