Structural Systematics of Rare Earth Complexes. XVI (‘Maximally’) Hydrated Rare Earth(III) Bromides

Abstract

Room-temperature single-crystal X-ray structure determinations carried out on rare earth bromides crystallized from water at room temperature define three series of hydrates LnBr₃.nH₂O. For Ln = La, Ce, a heptahydrate phase (n = 7) is defined, triclinic P 1, a ≈ 8·6, b ≈ 9·4, c ≈ 8·3 Å, α ≈ 108, β ≈ 99, γ ≈ 72°, isomorphous with the array described for the ‘early’ (Ln = La-Pr) rare earth chlorides, being binuclear [(H₂O)₇Ln(-Br)₂Ln(OH₂)₇] Br₄, Z = 1 dimer; conventional R on |F| were 0·051, 0·042 for 2323, 3451 independent ‘observed’ (I > 3σ(I)) diffractometer reflections respectively. For Ln = Pr(-)Dy, a hexahydrate phase is defined, monoclinic P 2/n, a ≈ 10·0, b ≈ 6·8, c ≈ 8·2 Å, β ≈ 93·5°, Z = 2 f.u., isomorphous with the array defined for the heavier (Ln = Nd, Lu, Y) rare earth chlorides, being [(H₂O)₆LnBr₂] Br, with R 0·029, 0·034 for N_o 1590, 1388 respectively. For Ln = Ho(-)Lu, Y, an octahydrate is defined for the first time, monoclinic P 2₁/n, a ≈ 8·1, b ≈ 16·0, c ≈ 10·1 Å, b ≈ 94·0°, Z = 4 f.u., a new array of the form [Ln(OH₂)₈] Br₃ emerging, with R 0·061, 0·048, 0·042 for N_o 1191, 2402, 1674 respectively, the metal environment being square antiprismatic.