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.