Determination of the relative ligand-binding strengths in heteroleptic Ir ~(III) complexes by ESI-Q-TOF tandem mass spectrometry

摘要

An electrospray ionization quadrupole time-of-flight mass spectrometer has been utilized to investigate the relative ligand-binding strengths in a series of heteroleptic-charged iridium(III) complexes of the general formula [(C^N) _2Ir ~(III)(S-tpy)](PF _6) by using variable collision energies. Collision-induced dissociation experiments were performed in order to study the stability of the Ir ~(III) complexes that are, for instance, suitable phosphors in light-emitting electrochemical cells. The ratio of signal intensities belonging to the fragment and the undissociated complex depends on the collision energy applied for the tandem mass spectra (MS/MS) analysis. By defining the threshold collision energy and the point of complete complex dissociation, it is possible to estimate the relative complex stabilities depending on the nature of the coordinated ligands [i.e. type of cyclometalating ligand (C^N), substituents on the S-shaped terpyridine (S-tpy)]. The collision energy values differed as a function of the coordination sphere of the Ir ~(III) centers.