A Series of Arsenotungstates Based on the [HAs₂W₈O₃₁]^7– Building Block: Syntheses by Control of the Reaction Process

A series of arsenotungstates formulated as (H2en)3.5­[HAs2­W8O31]·6H2O (1), Na0.5­(H2en)6.5­{Ni3­(en)­[B-α-As­W9O34]­[B-β-As­W8O31]}­Cl1.5·9H2O (2), and [H2en]4­{[Ni4­(Hen)2]­[B-α-As­W9O34]2}·5H2O (3) have been sequentially synthesized by controlling the reaction process. First, 1 was synthesized in an aqueous medium by the reaction of NiCl2 and Na­AsO2 with Na2­WO4, then colorless crystals of 1 transformed to yellow-green crystals of 2 for the further development of slow solvent evaporation, and, finally, yellow crystals of 3 generated over a sufficiently long time of solvent evaporation. 3 can also be hydrothermally synthesized in three different routes. Notably, 1 presents a [HAs2­W8O31]7– building block, 2 exhibits an asymmetric sandwich-type arsenotungstate encapsulating two nonequivalent Keggin fragments [B-α-As­W9O34]9– and [B-β-As­W8O31]9–, and 3 is composed of two [B-α-As­W9O34]9– units sandwiching a tetranickel cluster. Their structural difference indicates that controlling the reaction process plays a key role in the structures and topologies of these complexes