文摘
A series of arsenotungstates formulated as (H2en)3.5[HAs2W8O31]路6H2O (1), Na0.5(H2en)6.5{Ni3(en)[B-伪-AsW9O34][B-尾-AsW8O31]}Cl1.5路9H2O (2), and [H2en]4{[Ni4(Hen)2][B-伪-AsW9O34]2}路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鈥?/sup> building block, 2 exhibits an asymmetric sandwich-type arsenotungstate encapsulating two nonequivalent Keggin fragments [B-伪-AsW9O34]9鈥?/sup> and [B-尾-AsW8O31]9鈥?/sup>, and 3 is composed of two [B-伪-AsW9O34]9鈥?/sup> 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