By introduction of trilacunary Keggin-type polyoxometalate to the hydrothermal reaction system of Cr3+, Ln3+ and phthalic acid, a series of novel {Cr4Ln4} heterometallic clusters with the formula Cs2[Cr4Ln4(μ4-O)4(μ3-O)4(C8H4O4)4(H2O)12](H3SiW12O40)Cl·23H2O (1-Ln, Ln = Ce, Pr, Nd) and [Cr4Ln4(μ4-O)4(μ3-O)4(C8H4O4)4(H2O)10](H6SiW12O40)Cl2·18H2O (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.
![Graphical abstract: Incorporating polyoxometalates and organic ligands to pursue 3d–4f heterometallic clusters: a series of {Cr4Ln4} clusters stabilized by phthalic acid and [SiW12O40]4−](http://hg.y866.cn/compound/lib/scimg/usr/1/C9RA01731C.jpg)
