Cluster-based metal–organic frameworks (MOFs) supported by mixed ligands usually have unique properties due to the combined features from different ligands. In this regard, it is rather rare for carboxylate and pyrazolate ligands as “struts” to be present in one MOF. Herein, four isostructural heptanuclear Co(II)-based MOFs based on mixed carboxylate and pyrazolate ligands, [Co₇(μ₃-OH)₄(BDP)₂(IPA-X)₅] (BUT-127-X; X = H, OH, Br, and NH₂, respectively; BDP^2– = 1,4-benzenedipyrozolate and IPA^2– = isophthalate), were synthesized through carefully tuning the solvothermal reaction conditions. Structurally, in these MOFs, alternately connecting Co₇(μ₃-OH)₄ clusters with carboxylate ligands (IPA^2–-X) generate two-dimensional (2D) layers, which are further supported by the pyrazolate ligands (BDP^2–), giving rise to the final pillared-layer frameworks with well adjustable pore surface environments. They have permanent porosity with high Brunauer–Emmett–Teller surfaces from 1030 to 1314 m² g^–1, as well as good chemical stability. Interestingly, four Co(II) atoms in the Co₇(μ₃-OH)₄ cluster exhibit a five-coordinated configuration that affords open metal sites. The feature allows these MOFs to present good CO₂ adsorption performance and catalytic activity for the CO₂ fixation, where BUT-127-NH₂ gave the best catalytic performance for the cycloaddition of CO₂ with epoxides into cyclic carbonates under mild conditions (1 bar, 25 and 50 °C).

中文翻译：

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羧酸盐和吡唑酸盐配体的基于Co ₇的基于簇的金属有机骨架：结构，CO ₂吸附和固定

由于不同配体的综合特征，混合配体支持的基于簇的金属有机骨架（MOF）通常具有独特的性能。在这一点上，在一个MOF中很少存在羧酸根和吡唑根配体作为“支撑物”。在此，4同构heptanuclear钴（II）基的MOF基于混合羧酸盐和吡配体，[CO ₇（μ ₃ -OH）₄（BDP）₂（IPA-X）₅ ]（BUT-127-X; X =分别为H，OH，Br和NH ₂； BDP ^2– = 1,4-苯二吡^唑酯和IPA ^2–通过仔细调节溶剂热反应条件合成。在结构上，在这些的MOF，交替连接钴₇（μ ₃ -OH）₄簇与羧酸根配体（IPA ^2- -X）生成二维（2D）的层，其由配体吡进一步支持（BDP ^2-） ，从而产生具有可调节孔隙表面环境的最终柱状层框架。它们具有永久的孔隙度，其Brunauer-Emmett-Teller表面高，从1030到1314 m ² g ^–1，并且具有良好的化学稳定性。有趣的是，在共4的Co（II）原子₇（μ ₃ -OH）₄集群显示五坐标配置，提供了开放的金属站点。该功能使这些MOF表现出良好的CO ₂吸附性能和对CO ₂固定的催化活性，其中BUT-127-NH ₂在温和的条件下（1巴）将CO ₂与环氧化物环化成环状碳酸酯具有最佳的催化性能。，25和50°C）。