Hydrothermal syntheses and characterizations of 0D to 3D polyoxotungstates linked by copper ions

A new family of hybrid organic–inorganic materials built from polyoxotungstates and Cu(II) ions as linkers has been synthesized by hydrothermal reactions from a mixture of sodium tungstate, copper chloride and ethylenediamine. The initial pH and the presence or absence of heteroelement (P, Si) control the nature of the polyoxotungstate clusters and their connectivity via the copper ions, and hence the dimensionality of the framework. In the absence of heteroelement, three compounds have been isolated: at low pH (5) the molecular compound [Cu(en)2(H2O)]2[{Cu(en)2}H2W12O40] · 10H2O (1) is formed, at neutral pH the 3D material [{Cu(en)2}3{Cu(en)}2H2W12O42] · 27H2O (2) and at high pH (11) the 2D compound [Cu(en)2(H2O)2][Cu(en)2][{Cu(en)2}3H2W12O42] · 15H2O (3). In the whole range of pH (5–11.5) a single phase has been obtained with silicium as heteroelement, namely the 2D material [Cu(en)2(H2O)][{Cu(en)2}2SiW11CuO39] · 7H2O (4) with chains of Keggin polyoxotungstates linked by {Cu(en)2}2+ groups. Finally, a phosphotungstate with a chain-like structure has been characterized, [{Cu(en)2}3PW11CuClO39] · 6H2O (5), at low pH (5) which differs from the phase obtained at higher pH.