Influencing the Self‐Sorting Behavior of [2.2]Paracyclophane‐Based Ligands by Introducing Isostructural Binding Motifs

Abstract

Two isostructural ligands with either nitrile (Lnit) or isonitrile (Liso) moieties directly connected to a [2.2]paracyclophane backbone with pseudo‐meta substitution pattern have been synthesized. The ligand itself (Lnit) or its precursors (Liso) were resolved by HPLC on a chiral stationary phase and the absolute configuration of the isolated enantiomers was assigned by XRD analysis and/or by comparison of quantum‐chemical simulated and experimental electronic circular dichroism (ECD) spectra. Surprisingly, the resulting metallosupramolecular aggregates formed in solution upon coordination of [(dppp)Pd(OTf)2] differ in their composition: whereas Lnit forms dinuclear complexes, Liso exclusively forms trinuclear ones. Furthermore, they also differ in their chiral self‐sorting behavior as (rac)‐Liso undergoes exclusive social self‐sorting leading to a heterochiral assembly, whereas (rac)‐Liso shows a twofold preference for the formation of homochiral complexes in a narcissistic self‐sorting manner as proven by ESI mass spectrometry and NMR spectroscopy. Interestingly, upon crystallization, these discrete aggregates undergo structural transformation to coordination polymers, as evidenced by single‐crystal X‐ray diffraction.

Self-sorting assembly of artificial building blocks

“…Interestingly, the only difference between them was the element on the nearest carbon of the chiral nitrogen: one was O and the other was S. Similar results were observed when the atoms or groups changed their position on the molecules. 82,83 For instance, Yashima and co-workers changed the sequence of amide (NHCO or CONH) on cyclohexane derivates and totally changed their assembly behaviour (Fig. 7b and c).…”

“…Chan et al reported a series of terpyridine based multi-armed ligands that assembled with Cd 2+ into nanocapsules, 111 starlike structures, 28 triangles or hexagons. 111 Other structures like snowflake 112 and cage 83,113 were also achieved by varying the structure of ligands. Overall, this inspiring strategy has greatly expanded the ligand-based self-sorting assembly library, and was applicable in the synthesis of a metal complex with a controllable structure.…”

Heterochiral or Homochiral Self‐Assembly: Mercury(II), Cadmium(II), and Spontaneous Resolution of Silver(I) Complexes Derived from a Racemic Bis(pyridyl) Ligand

“…The solid-state fluorescence emission maxima of the racemic ligand were observed at 448 nm upon excitation at λ ex = 419 nm, which can be ascribed to the π-π* and n-π* transitions. The main emission peaks occur at 486 nm for 1, 462 nm for 2, 472 nm for 3, and 492 nm for 4, exhibiting a red shift (38,14,24, and 44 nm) as compared with the racemic ligand, which indicates that the emission of 1-4 may presumably be associated with metal to ligand charge-transfer transitions (MLCT). [43] In fact, the different emissions are also related to other factors, such as the coordination environments of the metal ions or solvent molecules in different complexes, as well as the formation of different structural types.…”

“…[22] Mastering the self-sorting behavior is of utmost importance to cope with the immense structural complexity that such systems offer. [23][24][25][26][27] Thus the exploration and understanding of the factors that affect the structural self-assembly is essential for crystal engineers who design structures, in particular those of materials based on coordination networks with racemic ligands. recognition or self-discrimination of the ligand units.…”

“…For example, Rudbari group has reported that the reaction of a racemic mixture of Schiff base tridentate ligand with vanadium(V) affords homochiral vanadium complex in a ligand self‐recognition process, and the Bian group reported that a racemic bisbipyridines ligand discriminates its own chirality and results in a heterochiral metallocycle in a chiral self‐discriminating manner . Mastering the self‐sorting behavior is of utmost importance to cope with the immense structural complexity that such systems offer . Thus the exploration and understanding of the factors that affect the structural self‐assembly is essential for crystal engineers who design structures, in particular those of materials based on coordination networks with racemic ligands.…”