Structural Systematics of Rare Earth Complexes. XX (Maximally) Hydrated Rare Earth Sulfates and the Double Sulfates (NH4)Ln(SO4)2.4H2O (Ln = La, Tb)

Abstract

Room-temperature single-crystal X-ray studies carried out on trivalent rare earth sulfate hydrates, Ln₂(SO₄)₃.xH₂O, crystallized at local ambience suggest the following arrays to be prevalent. For Ln = La, the nonahydrate is found, hexagonal P 6₃/m, with conventional R on |F| 0·023 for N_o 1159 ‘observed’ (I >3σ(I)) diffractometer reflections (redetermination). Although for Ln = Ce a similar structure has been previously recorded, we have obtained that adduct as the monoclinic C 2/c, Z = 4, octahydrate, a phase also found for Ln = Lu and diverse representative intermediate lanthanoids: a ≈ 13·6, b ≈ 6·6, c ≈ 18·2 Å, β ≈ 102°; for Ln = Ce (redetermination), Dy, Yb (redetermination), Lu, R was 0·022, 0·035, 0·031, 0·024 for N_o 3279, 2127, 3008, 3325 respectively. The structures of two lower hydrates adventitiously obtained are also recorded: the pentahydrate for Ln = Ce, monoclinic C 2/c, a 15·741(3), b 9·632(3), c 10·358(3) Å, β 119·72(2)°, Z = 4, R 0·030 for N_o 3372 (a redetermination), and the trihydrate for Ln = Lu, orthorhombic Cmc2₁, a 13·527(5), b 18·415(5), c 9·242(7) Å, Z = 8, R 0·040 for N_o 1743. All structures are infinite polymeric arrays, the lanthanoid atoms being bridged by sulfate ions. Studies are also recorded for the ammonium/trivalent rare earth double sulfate tetrahydrate salts, (NH₄)Ln(SO₄)₂.4H₂O, for the (hitherto) extremal members Ln = La, Tb, which are isomorphous with the previously studied Ln = Sm monoclinic P 2₁/c, Z = 4 array, a ≈ 6·6, b ≈ 19, c ≈ 8·8 Å, β 97°; R 0·035, 0·037 for N_o 3631, 3337. The array is a two-dimensional polymer, parallel to the ac plane.