Oxalate-bridging NdIII-based arsenotungstate with multifunctional NIR-luminescence and magnetic properties†
Abstract
Oxalate bridged Nd-based arsenotungstate, K14Na6H4[{(As2W19O67(H2O))Nd(H2O)2}2(C2O4)]·64H2O (1), was obtained from the reaction of K14[As2W19O67(H2O)], oxalic acid, and NdCl3·6H2O in mildly acidic aqueous solution. The polyanion exhibits a dimeric structure in which the fully deprotonated oxalate ligands bridge two NdIII cations and the arsenotungstate anions act as blocking ligands. The photoluminescence (PL) spectrum of 1 shows the characteristic emission peak of NdIII in the near-infrared (NIR) region. However, the O → W charge-transfer transitions of arsenotungstate cannot effectively sensitize the emission of NdIII cations as confirmed by the emission spectrum, due to the mismatch of the energy gap between 3T1u → 1A1g (21.57 × 103 cm−1) of arsenotungstate components and 4F3/2 → 4I9/2 (11.43 × 103 cm−1) of NdIII cations. Magnetic studies of 1 demonstrate its field-induced single-molecule magnet (SMM) behavior. Direct current magnetic susceptibility studies imply the weak ferromagnetic couplings present between the two neighboring NdIII cations. In addition, the synergy between the coordination configuration of NdIII cations and the intramolecular magnetic interaction was discussed.