Tetra-Ln 3+ -Implanted Tellurotungstates Covalently Modified by dl-Malic Acid: Proton Conduction and Photochromic Properties.

Three unique dl-malic acid covalently modified tetra-Ln 3+ -implanted tellurotungstates [H 2 (CH 3 ) 2 ] 9 NaH 9 [Ln 4 (H 2 O) 14 W 6 O 13 (OH) 5 (Mal) 2 (B-α-TeW 9 O 33 ) 4 ]·48H 2 O [Ln = La 3+ ( 1 ), Ce 3+ ( 2 ), Pr 3+ ( 3 ); H 3 Mal = dl-malic acid] were fabricated by reacting Na 2 TeO 3 , Na 2 WO 4 ·2H 2 O, Mal, and LnCl 3 ·6H 2 O with dimethylamine hydrochloride in an aqueous solution. The most prominent architectural feature of these compounds is the covalent connection mode of an organic ligand and a polyoxometallate backbone, which is relatively rare in the realm of polyoxotungstates. The tetrameric polyanion can be deemed as four [TeW 9 O 33 ] 8- fragments fused together via an intriguing hexanuclearity [W 6 O 13 (OH) 5 (Mal) 2 Ln 4 (H 2 O) 14 ] 13+ cluster. Impedance measurements manifest that all three complexes display splendid proton conduction properties, with an exceptional conductivity for 2 up to 2.48 × 10 -2 S·cm -1 under 85 °C and 95% relative humidity. Moreover, compounds 1 and 3 exhibited fast reversible photochromic properties with allochroic half-life periods t 1/2 of 1.046 and 0.544 min, respectively.