Pyrene-Functionalized\nRu-Catenated Metallacycles:\nConversion of Catenated System to Monorectangle through Aging

Molecular transformation behavior within a mechanically\ninterlocked\nsystem is often assisted by chemical manipulation, such as the inclusion\nof guest molecules, variation in the solution concentration, or swapping\nof solvents. We present in this report the synthesis of ruthenium\nmetal and π-conjugated pyrene-based (2 + 2)<sub>2</sub> catenated\nrectangles. Additionally, we discuss the structural conversion of\nthese catenated rectangles into monorectangles through adjustments\nin concentration and solvent composition. In the presence of a methanol\nsolution, a transformation into monorectangles was observed as the\nconcentration declined. However, interestingly, in the presence of\na nitromethane solution, an alteration in conformation to monorectangles\nwas noted by just standing at room temperature for a few hours without\nany chemical manipulation. Furthermore, theoretical calculations were\nstudied to provide insights into the formation of catenated structures\nover other potential ring-in-ring or Borromean-ring-type structures.\nThe computational study with the GFN2-xTB method combined with density\nfunctional theory (DFT) calculations showed that the lower binding\nenergy within the rectangles favors a catenated structure over other\npotential ring-in-ring or Borromean-ring-type structures. This work\nrepresents a new example of an intertwined structure that self-assembles\ninto a catenated ring rather than a ring-in-ring or Borromean ring\nand transforms into a monorectangle in nitromethane without the use\nof any template, alteration in solution concentration, or exchange\nof solvents, but simply by standing at room temperature.