Incorporating polyoxometalates and organic ligands to pursue 3d–4f heterometallic clusters: a series of {Cr(4)Ln(4)} clusters stabilized by phthalic acid and [SiW(12)O(40)](4−)

By introduction of trilacunary Keggin-type polyoxometalate to the hydrothermal reaction system of Cr(3+), Ln(3+) and phthalic acid, a series of novel {Cr(4)Ln(4)} heterometallic clusters with the formula Cs(2)[Cr(4)Ln(4)(μ(4)-O)(4)(μ(3)-O)(4)(C(8)H(4)O(4))(4)(H(2)O)(12)](H(3)SiW(12)O(40))Cl·23H(2)O (1-Ln, Ln = Ce, Pr, Nd) and [Cr(4)Ln(4)(μ(4)-O)(4)(μ(3)-O)(4)(C(8)H(4)O(4))(4)(H(2)O)(10)](H(6)SiW(12)O(40))Cl(2)·18H(2)O (2-Ln, Ln = Sm, Eu, Gd, Tb, Dy, Ho, Er) have been obtained. Single-crystal structural analyses show that 1-Ln and 2-Ln constitute the first cases of Cr–Ln heterometallic clusters stabilized by inorganic polyoxometalate anions and organic ligands. Optical spectra studies demonstrate that 1-Ln and 2-Ln are narrow-gap semiconductors with band gaps of about 1.5 eV. Magnetic investigation shows that compound 2-Dy is a potential single molecule magnet.