Oxalate-bridging Nd III -based arsenotungstate with multifunctional NIR-luminescence and magnetic properties.

Oxalate bridged Nd-based arsenotungstate, K 14 Na 6 H 4 [{(As 2 W 19 O 67 (H 2 O))Nd(H 2 O) 2 } 2 (C 2 O 4 )]·64H 2 O (1), was obtained from the reaction of K 14 [As 2 W 19 O 67 (H 2 O)], oxalic acid, and NdCl 3 ·6H 2 O in mildly acidic aqueous solution. The polyanion exhibits a dimeric structure in which the fully deprotonated oxalate ligands bridge two Nd III cations and the arsenotungstate anions act as blocking ligands. The photoluminescence (PL) spectrum of 1 shows the characteristic emission peak of Nd III in the near-infrared (NIR) region. However, the O → W charge-transfer transitions of arsenotungstate cannot effectively sensitize the emission of Nd III cations as confirmed by the emission spectrum, due to the mismatch of the energy gap between 3 T 1u → 1 A 1g (21.57 × 10 3 cm -1 ) of arsenotungstate components and 4 F 3/2 → 4 I 9/2 (11.43 × 10 3 cm -1 ) of Nd III 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 Nd III cations. In addition, the synergy between the coordination configuration of Nd III cations and the intramolecular magnetic interaction was discussed.