Three New Three-Dimensional Frameworks Based on Hepta‑,
Hexa‑, and Pentanuclear Cobalt Clusters Derived from Substituted
Isophthalic Acids: Synthesis, Structures, and Magnetic Properties
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Abstract
Three new cluster-based cobalt/carboxylate
frameworks, formulated as {[H<sub>3</sub>O][Co<sup>II</sup><sub>7</sub>(μ<sub>3</sub>-OH)<sub>3</sub>(MeO-ip)<sub>6</sub>(H<sub>2</sub>O)<sub>3</sub>]·4.5H<sub>2</sub>O}<sub><i>n</i></sub> (<b>1</b>), {[Co<sup>II</sup><sub>6</sub>(μ<sub>3</sub>-OH)<sub>2</sub>(Bu<sup>t</sup>-ip)<sub>4</sub>(Bu<sup>t</sup>-Hip)<sub>2</sub>(H<sub>2</sub>O)<sub>2</sub>]·2CH<sub>3</sub>CN}<sub><i>n</i></sub> (<b>2</b>), and {[Co<sup>II</sup><sub>5</sub>(Me-ip)<sub>4</sub>(Me-Hip)<sub>2</sub>(H<sub>2</sub>O)<sub>4</sub>]·6H<sub>2</sub>O}<sub><i>n</i></sub> (<b>3</b>) (MeO-H<sub>2</sub>ip = 5-methoxyisophthalic
acid, Bu<sup>t</sup>-H<sub>2</sub>ip = 5-<i>tert</i>-buthylisophthalic
acid, and Me-H<sub>2</sub>ip = 5-methylisophthalic acid) have been
synthesized by the hydro(solvo)thermal reactions of Co<sub>2</sub>(CO)<sub>8</sub> with the corresponding isophthalic acids in CH<sub>3</sub>CN, Pr<sup><i>i</i></sup>OH, and water. Single-crystal
X-ray diffraction studies reveal that <b>1</b> and <b>2</b> both exhibit a three-dimensional (3D) <b>pcu</b> net based
on hepta- and hexanuclear cobalt hydroxyl clusters {Co<sup>II</sup><sub>7</sub>(μ<sub>3</sub>-OH)<sub>3</sub>} and {Co<sup>II</sup><sub>6</sub>(μ<sub>3</sub>-OH)<sub>2</sub>}, respectively.
Compound <b>3</b> is a 3D porous framework with an eight-connected <b>bcu</b> 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 <b>1</b> and <b>2</b> show spin-canting antiferromagnetism, while <b>3</b> exhibits
a magnetocaloric effect (MCE). The resulting entropy change of <b>3</b> is 13.23 J kg<sup>–1</sup> K<sup>–1</sup> for
Δ<i>H</i> = 80 kG at 4 K
