Supramolecular Architectures and Magnetic Properties of Coordination Polymers Based on Pyrazinedicarboxylato Ligands Showing Embedded Water Clusters

The synthesis, crystal structure, and magnetic behavior of nine transition-metal complexes based on pyrazine-2,5-dicarboxylato (pz25dc) and pyrazine-2,3-dicarboxylato (pz23dc) ligands are reported. The pz25dc ligand displays
a bis-bidentate coordination mode, with the carboxylate groups almost coplanar with the pyrazine ring, to afford
polymeric 1-D chains [Mn(1), Fe(2), Zn(3), and Cu(4 and 5)] and discrete dimeric entities [Mn(6)] when the 1,10-phenanthroline (phen) blocking ligand is used to avoid further polymerization. The nonplanar pz23dc ligand chelates
to a unique copper center, while it bridges another one or two metal centers via the remaining carboxylate group,
leading to 1-D polymeric chains (7), ladder chains (8), and sheets (9). The crystal packing of the metal-organic
frameworks of compounds 4−9 generates voids which are occupied by assembled water molecules. The different
water cluster patterns (tapes, four-membered discrete rings, and chains for compounds 6, 8, and 9, respectively)
and their role in the cohesiveness of supramolecular architectures are analyzed. Thermogravimetric and variable-temperature X-ray powder diffraction studies have revealed the occurrence of reversible dehydration processes in
compounds 6, 8, and 9. Furthermore, the magnetic behavior of these compounds has been studied in order to
analyze the capability of the pyrazine ring to transmit magnetic interactions.

本文报道了9种基于吡嗪-2,5-二羧酸根（pyrazine-2,5-dicarboxylato，pz25dc）与吡嗪-2,3-二羧酸根（pyrazine-2,3-dicarboxylato，pz23dc）配体的过渡金属配合物的合成、晶体结构及磁学行为。其中pz25dc配体呈现双双齿配位模式，其羧酸根基团与吡嗪环近乎共平面；当使用1,10-邻菲啰啉（1,10-phenanthroline，phen）作为封闭配体以阻止进一步聚合时，可得到一维聚合物链[对应配合物1：Mn、2：Fe、3：Zn、4与5：Cu]以及离散二聚体实体[对应配合物6：Mn]。非平面构型的pz23dc配体可螯合至单个铜中心，同时通过剩余的羧酸根基团桥联另外一个或两个金属中心，进而构筑得到一维聚合物链（7）、梯状链（8）与层状结构（9）。配合物4~9的金属有机框架（metal-organic frameworks）经晶体堆积后形成孔洞，这些孔洞由组装的水分子填充。本文分析了配合物6、8、9对应的不同水簇结构——分别为带状、四元离散环与链状结构——及其在超分子架构凝聚性中的作用。热重分析与变温X射线粉末衍射研究证实，配合物6、8、9存在可逆脱水过程。此外，为探究吡嗪环传递磁相互作用的能力，本文对上述配合物的磁学行为展开了研究。