Self-Assembly of Supramolecular Porphyrin Arrays by Hydrogen Bonding: New Structures and Reflections

This study relates to the self-assembly of the free-base 5,10,15,20-tetrakis(4-carboxyphenyl)porphyrin (TCPP), six-coordinate manganese-5,10,15,20-tetrakis(4-carboxyphenyl)porphyrin with molecules of water or methanol as axial ligands
[MnIII(H2O)2-TCPP or MnIII(CH3OH)2-TCPP, respectively], and manganese chloride-5,10,15,20-tetrakis(4-hydroxyphenyl)porphyrin
[MnIII(Cl)-TOHPP] into multiporphyrin hydrogen-bonding “polymers”. In the first case, the porphyrin units hydrogen bond directly
to each other through their carboxylic acid functions. The two-dimensional (2D) square-grid polymeric arrays thus formed are
sustained by characteristic intermolecular cyclic dimeric (COOH)2 hydrogen-bond synthons between a given porphyrin unit and
four other neighboring species along the equatorial directions. They stack tightly one on top of the other in an offset manner along
the normal direction, yielding channeled lattice architecture. In an aqueous basic environment insertion of MnIII into the porphyrin
core involves deprotonation of one of the carboxylic groups, to balance the charge, and attraction of two water molecules as axial
ligands. The MnIII(H2O)2-TCPP units hydrogen bond, however, directly to one another through their carboxylic/carboxylate functions
in the equatorial plane in a catemeric (rather than cyclic dimeric) manner. The 2D networks that form in this case are interconnected
in the normal direction by additional hydrogen bonds through the axial water ligands, yielding a three-dimensional (3D) hydrogen-bonding architecture. In a methanolic solution of H3PO4, the methanol molecules replace water as axial ligands to the metal ion. The
phosphate anions balance the extra positive charge of the trivalent metal, and they act also as effective bridges between adjacent
MnIII(CH3OH)2-TCPP moieties by interacting as proton acceptors with the peripheral carboxylic functions of four different porphyrins.
This affords open square-grid-type layers with alternating porphyrin and phosphate components. The 2D arrays stack in an offset
manner, interconnecting to one another through hydrogen bonds involving the methanol axial ligands. The Mn(Cl)-TOHPP building
blocks arrange in a unique tetragonal structure around axes of 4-fold rotation and self-assemble through multiple O−H···Cl- attractions
between neighboring units into a single-framework hydrogen-bonding polymer. The directional asymmetry introduced to them by
the Cl-axial ligand, which is amplified by the preferred hydrogen-bonding scheme, induces the formation of a noncentrosymmetric
crystal structure. The nanoporous nature of TCPP-based multiporphyrin assemblies and the chirality of the Mn(Cl)-TOHPP structure
are highlighted.

本研究涉及游离基5,10,15,20-四(4-羧基苯基)卟啉（TCPP）的自组装，以及六配位锰-5,10,15,20-四(4-羧基苯基)卟啉（MnIII(H2O)2-TCPP或MnIII(CH3OH)2-TCPP，分别）和水或甲醇分子作为轴向配体的配合物，以及锰氯化物-5,10,15,20-四(4-羟基苯基)卟啉（MnIII(Cl)-TOHPP）自组装成多卟啉氢键“聚合物”。在前一种情况下，卟啉单元通过其羧基功能团直接相互氢键结合。因此形成的二维（2D）正方形网格聚合物阵列由特定卟啉单元与沿赤道方向的四个其他邻近物种之间的特征性分子间循环二聚（COOH）2氢键合成子维持。它们沿法线方向紧密堆叠，以错位方式排列，从而形成带状晶格结构。在碱性水溶液中，MnIII插入卟啉核心涉及一个羧基团的去质子化，以平衡电荷，并吸引两个水分子作为轴向配体。然而，MnIII(H2O)2-TCPP单元在赤道平面通过其羧基/羧酸盐功能团以猫聚（而非循环二聚）方式直接相互氢键结合。在这种情况下形成的二维网络通过轴向水配体在法线方向上的额外氢键相互连接，从而形成三维（3D）氢键结构。在H3PO4的甲醇溶液中，甲醇分子取代水作为金属离子的轴向配体。磷酸阴离子平衡三价金属的额外正电荷，并且它们通过与四个不同卟啉的周围羧基功能团作为质子受体相互作用，充当相邻MnIII(CH3OH)2-TCPP基元之间的有效桥梁。这提供了开放的正方形网格层，其中卟啉和磷酸成分交替。二维阵列以错位方式堆叠，通过涉及甲醇轴向配体的氢键相互连接。Mn(Cl)-TOHPP构建单元围绕四重旋转轴以独特的正方形结构排列，并通过相邻单元之间的多个O−H···Cl-相互作用自组装成单框架氢键聚合物。Cl-轴向配体引入的方向不对称性，通过优选的氢键方案得到放大，导致非中心对称晶体结构的形成。TCPP基多卟啉组装的纳米多孔性质和Mn(Cl)-TOHPP结构的手性被突出展示。