Three New Three-Dimensional Frameworks Based on Hepta‑, Hexa‑, and Pentanuclear Cobalt Clusters Derived from Substituted Isophthalic Acids: Synthesis, Structures, and Magnetic Properties

Three new cluster-based cobalt/carboxylate frameworks, formulated as {[H3O]­[CoII 7­(μ3-OH)3­(MeO-ip)6­(H2O)3]­·4.5H2O} n (1), {[CoII 6­(μ3-OH)2­(But-ip)4­(But-Hip)2­(H2O)2]­·2CH3CN} n (2), and {[CoII 5(Me-ip)4­(Me-Hip)2­(H2O)4]­·6H2O} n (3) (MeO-H2ip = 5-methoxyisophthalic acid, But-H2ip = 5-tert-buthylisophthalic acid, and Me-H2ip = 5-methylisophthalic acid) have been synthesized by the hydro(solvo)thermal reactions of Co2(CO)8 with the corresponding isophthalic acids in CH3CN, Pr i OH, and water. Single-crystal X-ray diffraction studies reveal that 1 and 2 both exhibit a three-dimensional (3D) pcu net based on hepta- and hexanuclear cobalt hydroxyl clusters {CoII 7(μ3-OH)3} and {CoII 6(μ3-OH)2}, respectively. Compound 3 is a 3D porous framework with an eight-connected bcu topology constructed from a pentanuclear cobalt cluster. It has been found that the structures of cobalt clusters in these compounds largely depend on the substituents on isophthalic acids. The magnetic studies indicate that both 1 and 2 show spin-canting antiferromagnetism, while 3 exhibits a magnetocaloric effect (MCE). The resulting entropy change of 3 is 13.23 J kg–1 K–1 for ΔH = 80 kG at 4 K.