Squaric acid-directed transformation of metal-organic macrocycles

Squaric acid directed the metal-organic PdnL2n macrocycles transforming into a more stable Pd4L8 square. This host-guest complex was characterized by NMR, ESI-TOF-MS, and X-ray crystallography. Multiple weak interactions, including electrostatic and hydrogen-bonding interactions, and the perfectly matched shape and size between the Pd4L8 square and squarate dianion well stabilized this host-guest complex, revealing the templating-effect of guest is crucial in supermolecular self-assembly. The stability of the PdnL2n macrocycles under acidic conditions paves the way for their further applications in organic catalysis.90