pH-Controlled and Sulfite Anion-Directed Assembly of a Family of Cerium(III)-Containing Polyoxotungstates Clusters

A versatile one-pot strategy was
employed to synthesize five cerium­(III)-containing polyoxotungstate
nanoclusters through pH-controlled and sulfite anion-directed assembly:
[C2H8N]3Na7[Ce2(H2O)6W22O72(OH)4]·20H2O (1) at pH 5.0; [C2H8N]8Na16[Ce4(H2O)12W44O144(OH)12]·23H2O (2) at pH 4.5; [C2H8N]2Na4Ce2[Ce2(H2O)10W28O92(OH)2]·27H2O (3) at pH 2.8–3.3;
[C2H8N]2Na7[{α-SW7O28}­{Ce2(H2O)6}­(W3O6)­{α-SW9O32}­{α-SW9O31(OH)}]·18H2O (4) at pH 2.5; [C2H8N]2Na18[Ce2(H2O)9W36O110(OH)12]2·30H2O (5) at pH 1.5. These compounds were characterized
by single-crystal X-ray structure analysis, IR spectroscopy, thermogravimetric
(TG) analysis, X-ray photoelectron spectroscopy (XPS), and electrospray
ionization mass spectrometry (ESI-MS). Moreover, their electrochemical
properties were investigated. Single-crystal X-ray structure analysis
revealed that 1 and 2 were di- and tetra-cerium­(III)-bridged
polyoxotungstates, constructed from two different types of lacunary
{W11} units. 3 composed of the well-known
cerium­(III)-stabilized {W28} unit and organic amine–sodium–cerium
cations, was isolated in the pH range 2.8–3.3. In this reaction
system, the SO32– anion acted as a heteroanion
template at a lower pH 2.5. 4 was isolated by the combination
of cerium­(III) centers and SO32– heteroanion
template, which is the first lanthanide-containing polyoxotungstates
with sulfur heteroatoms, and the 4f metal cerium­(III) centers in 4 both have eight-coordinated modes and the SO32– heteroanion templates display μ7 and μ9 coordination modes. At a much lower pH 1.5,
the polyanion of 5 was obtained, two triangular-shaped
{W36} subunits were bridged by the cerium­(III) ions, resulting
in the largest lanthanide-containing iso-polyoxotungstates known to
date.