By　introduction　of　trilacunary　Keggin-type　polyoxometalate　to　the　hydrothermal　reaction　system　of　Cr3+,　Ln(3+)　and　phthalic　acid,　a　series　of　novel　{Cr(4)Ln(4)}　heterometallic　clusters　with　the　formula　Cs-2[Cr(4)Ln(4)(mu(4)-O)(4)(mu(3)-O)(4)(C8H4O4)(4)(H2O)(12)](H3SiW12O40)Cl　center　dot　23H(2)O　(1-Ln,　Ln　=　Ce,　Pr,　Nd)　and　[Cr(4)Ln(4)(mu(4)-O)(4)(mu(3)-O)(4)(C8H4O4)(4)(H2O)(10)](H6SiW12O40)Cl-2　center　dot　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.