Two Pairs of Chiral "Tower-Like" Ln4 Cr4 (Ln=Gd, Dy) Clusters: Syntheses, Structure, and Magnetocaloric Effect.

Two pairs of novel chiral chromium lanthanide compounds, formulated as l- and d-[Gd4 Cr4 (IN)10 (μ3 -OH)4 (μ4 -O)4 (H2 O)12 ]⋅[IN]2 ⋅8 H2 O (1 and 3), and l- and d-[Dy4 Cr4 (IN)11 (μ3 -OH)4 (μ4 -O)4 (H2 O)8 ]⋅[IN]⋅1.5 H2 O (2 and 4) (HIN=isonicotinic acid) have been successfully synthesized and characterized. Structural analysis reveals that four Ln3+ ions and four Cr3+ ions connect with each other and yield a "tower-like" [Ln4 Cr4 ] skeleton. Apart from the above featuring an aesthetically charming structure, circular dichroism (CD) spectra confirm that compounds 1 and 3, 2 and 4 are enantiomers. To the best of our knowledge, these are the largest chiral chromium lanthanide compounds. In addition, magnetic interaction shows that Gd (the mixture of 1 and 3) exhibits significant cryogenic magnetocaloric effect (MCE) with -ΔSm =18.08 J kg-1  K-1 (34.69 mJ cm-3  K-1 ). Also, the observed second-harmonic generation efficiencies of [Gd4 Cr4 (IN)10 (μ3 -OH)4 (μ4 -O)4 (H2 O)12 ]⋅[IN]2 ⋅8 H2 O and [Dy4 Cr4 (IN)11 (μ3 -OH)4 (μ4 -O)4 (H2 O)8 ]⋅[IN]⋅1.5 H2 O are 0.3 and 0.4 times that of urea, respectively.