Halide-templated assembly of polynuclear lanthanide-hydroxo complexes

A series of pentadecanuclear lanthanide-hydroxo complexes possessing a common core of the formula [Ln₁₅(μ₃OH)₂₀ (μ₅-X)]²⁴⁺(1, Ln = Eu, X = Cl^-; 2, Ln = Nd, X = Cl^-; 3, Ln = Gd, X = Cl^-; 4, Ln = Pr, X = Br^-; 5, Ln = Eu, X = Br^-) were prepared by L-tyrosine-controlled hydrolysis of corresponding lanthanide perchlorates in the presence of added Cl^- or Br^-. The cationic cluster core comprises five vertex-sharing cubane-like [Ln₄(μ₃-OH)₄]⁸⁺ units centered on the halide template. In the case of templating I^-, dodecanuclear complexes were isolated instead. The core component, [Ln₁₂(μ₃-OH)₁₆ (I)₂]¹⁸⁺ (6, Ln = Dy; 7, Ln = Er), consists of four vertex-sharing cubane-like [Ln₄(μ3-OH)₄]⁸⁺ units and exists as a square-shaped cyclic structure with one I- located on each side of the square plane. An analogous hydrolytic reaction involving Er(NO₃)₃, L-tyrosine, and NaOH affords the known hexanuclear complex [Er₆(μ6-O)(μ₃-OH)₈ (NO₃)₆(H₂O)₁₂] (NO₃)₂ whose core component is a face-capped octahedral [Er₆(μ₆-O)(μ₃- OH)₈]⁸⁺ cluster with an interstitial μ₆-oxo group (Wang, R.; Carducci, M. D.; Zheng, Z. Inorg. Chem. 2000, 39, 1836-1837.). The efficient self-assembly of halide-encapsulating multicubane complexes (1-7) and the inability to produce an analogous nitrate-containing complex demonstrate the superior templating roles played by the halide ion(s). Further credence for the halide template effects was provided by the isolation of the cationic pentadecanuclear complex 3 as the sole product when tyrosine-supported hydrolysis of Gd(NO₃)₃ was carried out in the presence of competitive Gl-Cl-. Magnetic moments of complexes 1-7 measured at room temperature by using Evans' method are in excellent agreement with those calculated by the Van Vleck equation, assuming magnetically noninteractive lanthanide ions.