A novel Keggin-type tungstogermanate dimer bearing dinuclear copper-organic coordination ions: {H8[Cu(phen)(μ2-CH3COO)2Cu(phen)(H2O)]2[Ge2W23CuO80]}·24H2O

Fe2 and Fe4 Clusters Encapsulated in Vacant Polyoxotungstates: Hydrothermal Synthesis, Magnetic and Electrochemical Properties, and DFT Calculations

“…[22] The splitting in complex 4 is thus close to the largest splittings observed in the family of monosubstituted lacunary derivatives. The splitting in complex 2 is more along the order of the values reported for [PW 11 O 39 Fe [23] and the splitting in complex 1 is close to the zero splitting value of the saturated [PW 12 O 40 ] 3À anion. The increasing value of Dn from complexes 1 to 4 can be tentatively explained by weaker interactions between the metal and the POM as shown by the significant elongation of the FeÀOA C H T U N G T R E N N U N G (PO 3 ) bond from complex 1 to complex 4 ( Table 1, see also the structural description below).…”

“…[6] Most of these POM compounds are synthesized by the direct reaction of the lacunary precursor with transition-metal ions under mild conditions (ambient pressure, T < 100 8C). The use of hydrothermal conditions with preformed POMs as precursors has so far been limited to mainly saturated Keggin anions such as [SiW 12 O 40 ] 4À , leading to materials with isolated transition-metal ions. [7] A rare example of a vacant POM introduced in a hydrothermal reactor, [SiW 10 O 36 ] 8À , has led to the neutral molecular complex [Cu 2 - O 40 ] (bpy = bipyridine), because of the instability of the lacunary precursor.…”

“…[8] It is only very recently that the first example of the successful use of lacunary POMs as precursors (i.e., with conservation of the introduced lacunary POM ligand) has been reported, affording monomeric hexanuclear clusters. [9] On the other hand, numerous structures of polyoxotungstates synthesized with Na 2 WO 4 as a precursor and under hydrothermal conditions have been described in the last few years, giving access to materials based on isopolyoxotungstates, [10] phosphotungstates, [10b, 11] germanotungstates, [12] and silicotungstates [10b, 11d, 13] building units, according to the presence or absence of a heteroelement. It should be noted that when tungstate is used as a precursor in such conditions, so far it has been difficult, if at all possible, to control the nature of the resulting POM ligand.…”