Self-assembly of [β-As(V)W8O31]9− subunit in hydrothermal system with moderate acidity: Synthesis, crystal structure and characterizations of dimeric arsenotungstate H2[{Cu(phen)}8(β-AsW8O31)2] · 2.5H2O

A novel dimeric arsenotungstate based on tetravacant subunit, H2[{Cu(phen)}8(β-AsW8O31)2] · 2.5H2O (phen = 1,10-phenanthroline) 1, has been prepared by hydrothermal methods with moderate acidity and characterized by elemental analyses, IR (25–650 °C), EPR, XPS, TG–DTA, and single-crystal X-ray diffraction. The title compound represents the first arsenotungstate example based on tetravacant Keggin polyanions. Furthermore, the comparison of image with few known tetravacant blocks exhibits the variety of image family in synthesis methods and existent forms.