An organic–inorganic hybrid dimeric arsenotungstate [enH2]4{[Cu(en)2][(A-β-H2AsW9O34)Cu(en)2]2}·8H2O established by two trivacant Keggin [A-β-AsW9O34]9− fragments in the opposite orientation

A novel organic–inorganic hybrid dimeric arsenotungstate [enH2]4{[Cu(en)2][(A-β-H2AsW9O34)Cu(en)2]2}·8H2O (1) has been prepared by reaction of Na8[A-α-HAsW9O34]·11H2O with CuCl2·2H2O and ErCl3 in the presence of ethylenediamine (en) under hydrothermal conditions and structurally characterized by elemental analyses, IR spectra, UV spectra, powder X-ray diffraction (PXRD) and single-crystal X-ray diffraction. The skeleton of 1 exhibits an interesting centric dimeric structure formed by two opposite trivacant Keggin [(A-β-H2AsW9O34)Cu(en)2]5− subunits linked by a [Cu(en)2]2+ connector, which represents a rare organic–inorganic hybrid arsenotungstate consisting of [A-β-AsW9O34]9− fragments. Interestingly, the trivacant Keggin precursor [A-α-AsW9O34]9− has been isomerized to the trivacant Keggin fragment [A-β-AsW9O34]9− in 1 under hydrothermal conditions. The photocatalytic measurement illustrates that 1 can effectively inhibit the photodegradation of rhodamine-B.