Self-assembly of triangular metallomacrocycles using unsymmetrical bisterpyridine ligands: isomer differentiation via TWIM mass spectrometry

Three unsymmetrical, 60 degrees-bended bisterpyridine ligands with varying phenylene spacer lengths have been synthesized via the Suzuki-Miyaura coupling reactions. Their self-assembly processes were found to be strongly dependent on the ligand geometry. Upon complexation with Zn-II ions, only 2,4 ''-di(4'-terpyridinyl)- 1,1':4',1 ''-terphenyl underwent self-selection to give a trinuclear metallomacrocycle with perfect heteroleptic connectivity and the other two afforded a mixture of constitutional isomers. The metallosupramolecular assemblies were characterized by NMR spectroscopy, electrospray mass spectrometry (ESI MS), and single-crystal X-ray diffraction. In particular, the identification of isomeric architecture was accomplished using tandem mass spectrometry (MS2) coupled with traveling wave ion mobility mass spectrometry (TWIM MS).