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]­[CoII7­(μ3-OH)3­(MeO-ip)6­(H2O)3]­·4.5H2O}n (1), {[CoII6­(μ3-OH)2­(But-ip)4­(But-Hip)2­(H2O)2]­·2CH3CN}n (2), and {[CoII5(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, PriOH, 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 {CoII7(μ3-OH)3} and {CoII6(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.