Metal‐Ion Tuning in Triple‐Stranded Helicate‐Based Metallosupramolecules

Abstract

Effective incorporation of multiple types of ligands in a given coordination structure provides structural complexity and functional diversity to the resultant coordination‐driven assembly. One of the most widely used synthetic approaches is the utilization of the molecular symmetry principle to combine multiple ligands and specific metallic centers in a preferred manner. The variation of metal ions can be helpful to understand the importance of symmetry for the generation of structurally hierarchical supramolecular platforms. We describe the synthesis and characterization of isostructural supramolecular helicates, [M8(PDA)6(AIP)3(DMF)6−x(H2O)x] (M=Ni (1), Co (2), and Mn (3); PDA=2,6‐pyridinedicarboxylate; AIP=5‐aminoisophthalate; x=0 for 1, and x=4 for 2 and 3). The effect of metal variation on the formation of supramolecular helicates and their solid‐state crystal packing are discussed. Despite the disparity in the ionic radii and distinct coordination‐geometry preferences of Co2+, Ni2+, and Mn2+, all metal centers engaged in the assembly with the heteroleptic ligands in the same manner to form isostructural supramolecular helicates.

Heteroleptic Triple-Stranded Metallosupramolecules with Hydrophobic Inner Voids

“…Note that the coordinated solvents in terminal nickels may not be the same in every experiment. The metal clusters possess chirality, either clockwise or counterclockwise, which is similar to the reported structures. − Each discrete supramolecule of 1 is constructed from two metal clusters with opposite chirality, resulting in a meso-helicate (Figure ). The existence of one mirror plane of symmetry passing through the middle point of the three CH 3 -TP ligands initiates C 3h symmetry of the meso-helicate.…”

“… 42 , 43 The oxidation state of nickel ions was determined to be +2 by the presence of two strong peaks at 855.98 and 873.11 eV standing for Ni 2p 3/2 and Ni 2p 1/2 , respectively ( Figure S7d ). 35 , 36 The bond valence sum calculation also revealed that nickel ions in these clusters have a +2 oxidation state ( Table S2 ). 44 , 45 The measurement of temperature-dependent magnetization (emu/g) of 1 was conducted using a Quantum Design MPMS3 magnetometer for temperatures 3 K ≤ T ≤ 300 K with 1000 Oe applied fields ( Figure S8a ).…”

“…CH 3 -H 2 TP (5′-methyl-[1,1′:3′,1′′-terphenyl]-4,4′′-dicarboxylic acid) and HO-H 2 TP (5′-hydroxy-[1,1′:3′,1′′-terphenyl]-4,4′′-dicarboxylic acid) were synthesized through a Suzuki coupling reaction according to the method reported in the literature with a slight modification. − Similar to H 2 PTA (benzene-1,3-dicarboxylic acid) and H 2 CDBA (4,4′-carbonyl­dibenzoic acid) used in the syntheses of the previously reported triple-stranded supramolecules, − both CH 3 -H 2 TP and HO-H 2 TP are ditopic ligands with a bending angle of ∼120° (Scheme ). The fundamental difference between substituted H 2 TP ligands and H 2 PTA or H 2 CDBA lies in their length and flexibility, that is, the distance between the carbon atoms in the two carboxyl groups of H 2 TP ligand is significantly longer than those of H 2 PTA and H 2 CDBA (Scheme ).…”

“…Depending on the substituent/functional group attached to C5 of the PTA ligand, various higher-order assembly modes were obtained such as discrete, polymeric, and cage metallosupramolecules. 31 − 35 When moving from a one-benzene ring system (PTA) to a two-benzene ring system (CDBA), TSHs could also be obtained with C 3 symmetry. 36 The inner voids surrounded by three CDBA ligands are larger than those surrounded by three PTA derivative ligands.…”

“…In our reported works, we have reported a range of supramolecules in which metal ions (Co 2+ , Ni 2+ , or Mn 2+ ) coordinated with 2,6-pyridine­dicarboxylate (PDA) to form tetranuclear metal clusters (primary assembly), and two metal clusters are interlinked by three bridging ligands, that is, benzene-1,3-dicarboxylate (PTA) derivatives or 4,4′-carbonyl­dibenzoate (CDBA), to form triple-stranded helicates (TSH) with C 3 symmetry. − For supramolecules constructed from PTA derivative, three bridging ligands with a bending angle of 120° create an empty space within the supramolecule. Depending on the substituent/functional group attached to C5 of the PTA ligand, various higher-order assembly modes were obtained such as discrete, polymeric, and cage metallo­supramolecules. − When moving from a one-benzene ring system (PTA) to a two-benzene ring system (CDBA), TSHs could also be obtained with C 3 symmetry . The inner voids surrounded by three CDBA ligands are larger than those surrounded by three PTA derivative ligands.…”