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

• Published in: Journal of mass spectrometry. 2012-01, Vol.47 (1), p.34-40
• Main Authors: Altuntaş, Esra, Winter, Andreas, Baumgaertel, Anja, Paulus, Renzo M, Ulbricht, Christoph, Crecelius, Anna C, Risch, Nikolaus, Schubert, Ulrich S
• Format: Article
• Language: English
• Subjects: Cations - chemistry; Coordination Complexes - chemistry; Iridium - chemistry; Ligands; Pyridines - chemistry; Rhodium - chemistry; Spectrometry, Mass, Electrospray Ionization - methods; Tandem Mass Spectrometry - methods
• ISSN: 1096-9888
• DOI: 10.1002/jms.2023

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)(2) Ir(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.