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][Co-7(II)(mu(3)-OH)(3)(MeO-ip)(6)(H2O)(3)]center dot 4.5H(2)O}(n) (1), {[Co-6(II)(mu(3)-OH)(2)(Bu-t-ip)(4)(Bu-t-Hip)(2)(H2O)(2)]center dot 2CH(3)CN}(n) (2), and {[Co-5(II)(Me-ip)(4)(Me-Hip)(2)(H2O)(4)]center dot 6H(2)O}(n) (3) (MeO-H(2)ip = 5-methoxyisophthalic acid, Bu-t-H(2)ip = 5-tert-buthylisophthalic acid, and Me-H(2)ip = 5-methylisophthalic acid) have been synthesized by the hydro(solvo)thermal reactions of Co-2(CO)(8) with the corresponding isophthalic acids in CH3CN, (PrOH)-O-i, 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)(mu(3)-OH)(3)} and {Co-6(II)(mu(3)-OH)(2)}, respectively. Compound 3 is a 3D porous framework with an eight-connected bcu topology constructed from a pentanuclear cobalt duster. It has been found that the structures of cobalt dusters 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 Delta H = 80 kG at 4 K.