Three new three-dimensional frameworks based on hepta-, hexa-, and pentanuclear cobalt clusters derived from substituted isophthalic acids: Synthesis, structures, and magnetic properties

摘要

Three new cluster-based cobalt/carboxylate frameworks, formulated as {[H_3O][Co _7~(II)(μ_3-OH) _3(MeO-ip)_6(H_2O)_3]·4.5H _2O}_n (1), {[Co_6~(II) (μ_3- OH)_2(But-ip)_4(But-Hip) _2(H_2O)_2]·2CH_3CN}_n (2), and {[Co _5~(II)(Me-ip)_4(Me-Hip) _2(H_2O)_4]·6H_2O}_n (3) (MeO-H_2ip = 5-methoxyisophthalic acid, Bu~t-H _2ip = 5-tert-buthylisophthalic acid, and Me-H_2ip = 5-methylisophthalic acid) have been synthesized by the hydro(solvo)thermal reactions of Co_2(CO)_8 with the corresponding isophthalic acids in CH_3CN, Pr~iOH, 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 {Co _7~(II)(μ_3-OH)_3} and {Co _6~(II)(μ_3-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.