Self‐Assembly Processes of Pd(II)‐ and Pt(II)‐Linked Discrete Self‐Assemblies Revealed by QASAP

Abstract

Recent progress in the understanding of discrete coordination self‐assembly processes is summarized. Aiming to make the problems in the investigation of molecular self‐assembly processes clear, a novel method (QASAP: quantitative analysis of self‐assembly process) to obtain the information about all intermediates that are transiently produced during the self‐assembly in an indirect way was introduced. Through the application of QASAP to over ten kinds of Pd(II)‐ or Pt(II)‐linked discrete coordination self‐assemblies, similarities between molecular self‐assembly and protein folding, general principles underlying coordination self‐assembly, and the mechanism of homochiral self‐sorting along the self‐assembly pathway have been revealed and are discussed below.

Bifurcation of self-assembly pathways to sheet or cage controlled by kinetic template effect

“…The order of the binding strength for anions is ClO 4 − > BF 4 − > ReO 4 − > PF 6 − , which suggests that smaller anions are more strongly bound in the cage with the exception that ClO 4 − (62.5 Å 3 ) is a better guest than BF 4 − (49.3 Å 3 ) 36 . The self-assembly of the cage from 1 and [PdPy* 4 ](OTf) 2 in CD 3 NO 2 at 298 K was carried out to investigate the intermediates produced during the selfassembly by QASAP (quantitative analysis of self-assembly process) [37][38][39] . In our previous research on the self-assembly process of this cage from 1 and [PdPy* 4 ](BF 4 ) 2 , a 200-nm-sized sheet structure was transiently produced during the self-assembly and this sheet structure was finally converted to the (BF 4 − )@ [Pd 2 1 4 ] 4+ cage 40 .…”

“…Investigation of the self-assembly process of the cage. The selfassembly process of the cage was investigated by the n-k analysis [37][38][39] and Py*). The change in the (〈n〉, 〈k〉) value with time suggests the type of occurring reactions and the mainly produced intermediates during the self-assembly.…”

Self-assembly process of a quadruply interlocked palladium cage

“…In order to investigate the intermediates for the Pd 2 1 4 cage and for the Pd 4 1 8 IC, n-k analysis [27][28][29][30] was carried out. In QASAP, two parameters (〈n〉 and 〈k〉) indicating the nature of Int (whose average composition is indicated as Pd 〈a〉 1 〈b〉 Py* 〈c〉 ) are defined and used for the characterization of the intermediates.…”

“…However, how molecular building blocks assemble into such complicated interlocked structures has rarely been discussed 26 mainly because the observation of transiently produced intermediates, whose stability is lower than the final product, is quite difficult. Recent progress in the investigation of coordination self-assembly processes by a method that can provide information about intermediates by quantifying all substrates and products instead of intermediates (QASAP: quantitative analysis of self-assembly process) has gradually unveiled ordering processes of supramolecular self-assemblies at the molecular level [27][28][29][30] .…”

Unlocking the computational design of metal–organic cages

“…123 By understanding the self-assembly process one can access and evaluate the potential intermediates via methods like above. On this path, substantial work done by Hiraoka and co-workers in quantitative (QASAP) and numerical (NASAP) analysis of self-assembly processes, with a specific focus on Pd and Pt-based MOC assembly, 124,125 provides a map of complex cage-assembly processes. Their numerical, reaction-network analysis can reproduce experimental intermediate populations and uncover kinetically trapped species.…”