Monitoring the mechanism of formation of [Ce(1,10-phenanthroline)2(NO3)3] by in situ luminescence analysis of 5d–4f electronic transitions

Abstract

This work introduces the application of the in situ luminescence analysis of coordination sensors (ILACS) technique for monitoring the emission of Ce³⁺ 5d–4f electronic transitions under real reaction conditions during the formation of [Ce(phen)₂(NO₃)₃] (phen = 1,10-phenanthroline). The mechanism of formation indicated by the ILACS data was confirmed by several additional methods, including ex situ and synchrotron-based in situ X-ray diffraction (XRD) analysis, in situ light transmission, and in situ infrared (IR) spectroscopy, among others. Initially, the in situ luminescence measurements presented a broad emission band at 415–700 nm, which was assigned to the Ce³⁺ ions in ethanolic solution. Upon the addition of the phen solution to the reactor, a gradual shift of the emission band to lower energies (500–900 nm) was observed. This occurs due to the changes in the Ce³⁺ coordination environment during its incorporation into the solid [Ce(phen)₂(NO₃)₃] complex. In situ IR measurements during the crystallization of [Ce(phen)₂(NO₃)₃] confirmed the kinetics of the crystallization process by detecting changes in the phen and nitrate vibrations at e.g. 842 and 1301 cm⁻¹, respectively. Simultaneous in situ XRD measurements confirmed the induction time of approximately 3 minutes after the addition of the phen solution, previously detected by the in situ luminescence measurements, coinciding with the onset of the [Ce(phen)₂(NO₃)₃] Bragg reflections. In situ monitoring of events occurring during the formation of solid materials is a crucially important step for developing rational synthesis approaches and for tailoring structure-related properties, such as luminescence.