pH-controlled construction of lanthanide clusters from lacunary polyoxometalate with single-molecule magnet behavior

Six lanthanide clusters were synthesized via pH-controlled strategy: Na-18[Ln(4)(Sb3O2)(2)(SbW10O37)(2)(SbW8O31)(2)(H2O)(6)]center dot(H2O)(60) [Ln = Dy3+ (1), Ho3+ (2), Er3+(3)) in pH 5.5 NaAc-HAc buffer solution displaying tetrameric architectures, and Na-23(Ln(3)(SbW9O33)(3)(CH3COO)(3)(WO4) (H2O)(3)]center dot(H2O)(50) [Ln = Dy3+ (4), Ho3+ (5), Er3+ (6)] in pH 7.2 NaAc/HAc solution featuring trimeric aggregates. Obviously, pH-controlled strategy can design the structures of lanthanide clusters. Moreover, the ac magnetic susceptibilities proved that compounds 1 and 4 manifested apparent slow magnetic relaxation behaviors. Interestingly, compound 1 exhibited both temperature- and frequency-dependent in-phase (chi') and out-of-phase (chi '') ac signals, behaving as a zero-field SMM with U-eff = 46.8 K, tau(0) = 8.11 x 10(-7) s calculated on the basis of Orbach process, and U-eff = 58.2 K, tau(0) = 3.63 x 10(-7) s according to Raman and Orbach relaxation processes. Compound 4 was found to be a SMM with a fast QTM, yielding a reversal barrier U-eff = 1.12 K with tau(0) = 9.27 x 10(-6) s.