Structural Systematics of Rare Earth Complexes. XXII. ('Maximally') Hydrated Rare Earth Iodides

Abstract

Low-temperature (c. 153 K) single-crystal X-ray structure determinations, carried out on trivalent rare earth iodides crystallized from aqueous solution at room temperature, have defined two series of hydrates, LnI₃.nH₂O. For Ln = La–Ho, a nonahydrate phase (n = 9) is defined, orthorhombic Pmmn, a ~ 11.5, b ~ 8.0, c ~ 8.8 Å, Z = 2, the second phase (n = 10), monoclinic P2₁/c, Z = 4 being defined for Ln = Er–Lu, a ~ 8.2, b ~ 12.8, c ~ 17.1 Å, β ~ 103.7˚. Neither of these phases is isomorphous with any of those pertinent to the previously studied chloride or bromide (hydrated) arrays, nor, unlike those, does the halide (iodide) in any case enter the coordination sphere of the lanthanoid. The n = 9 phase takes the form [Ln(OH₂)₉]I₃, the nine-coordinate lanthanoid environment stereochemistry being tricapped trigonal-prismatic, while the n = 10 phase is [Ln(OH₂)₈]I₃.2H₂O, the eight-coordinate lanthanoid environment being square-antiprismatic.