## 1 Introduction  
Time-resolved chemical dynamics experiments exploiting hard X-radiation have become a mainstream option over the past 20 years, and also part of the vast field of Femtochemistry [1]. This application was driven by the desire to add new observables to the portfolio of otherwise optical laser-based techniques, which can offer additional information about the electronic and molecular structural changes during the course of a chemical reaction. Early proof-of-principle studies used intense synchrotron radiation (SR) [2; 3; 4] as well as laser-driven plasma sources [5] for this purpose. While the X-ray plasma sources offered superior picosecond and even sub-picosecond time resolution at the expense of flux, the synchrotron studies improved their signal to noise ratios, but remained limited to around 50-100 ps. Therefore, X-ray absorption spectroscopy (XAS) including X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) investigations were far from being able to study structural wavepacket dynamics, but were already able to investigate short-lived reaction intermediates with lifetimes well below 1 ns [2; 4; 6; 7]. The improving signal quality of these time-resolved X-ray experiments triggered new studies towards improved modeling and theoretical interpretation of the measurements. This was performed for both time-resolved XANES and EXAFS studies [8; 9; 10; 11], while in parallel the structural interpretation of related time-resolved wide-angle X-ray scattering (WAXS) results [12; 13; 14; 15] improved considerably. This allowed for comparison of both complementary structural tools on the same time-resolved experiment, where [PERSON] et al. [6] analyzed the recorded time-resolved EXAFS of a photoexcited Pt-POP compound, while [PERSON] et al. [12] analyzed the pump-probe WAXS signals from the same molecule, yielding nearly identical results. In view of the difficulty to model the excited state structures in an unambiguous fashion, it is highly attractive to employ complementary structural tools for the same sample and experiment [10; 16; 17]. This also marks the strategy of the FXE instrument design at European XFEL: to enable complementary structural dynamics tools quasi-simultaneously. X-ray emission spectroscopy (XES) studies with 100 ps temporal resolution on photoexcited molecules in the solution phase were introduced by [PERSON] and colleagues at the Swiss Light Source [18], and were soon extended towards the first resonant inelastic X-ray scattering study with 100 ps time resolution [19]. This move opened the path for introducing more advanced X-ray spectroscopic techniques into the time domain with SR, and meanwhile K\(\alpha\), K\(\beta\) and even valence-to-core XES studies were successful [10; 11; 20; 21]. One new ingredient delivered by XES is the spin sensitivity around transition metal (TM) ions in photoactive TM complexes, and this property is now being used to unravel the intermediate (spin) states in the excited state manifold [22; 23; 24], which are extremely difficult to obtain with optical tools on the subnanosecond time scales. It also quickly became clear that studying photoexcited solutes using XES and WAXS (or solution scattering) in the same experiment can provide a deeper understanding of the interplay between structural and electronic structural dynamics. This was then demonstrated with SR [10; 16] and XFEL [25; 26; 27; 24] radiation in benchmarking studies, and today most hard X-ray FEL sources do include XES capabilities next to forward scattering, underlining the important steps undertaken in the past to open this new technological tool for structural dynamics studies with femtosecond time resolution. Below we present one result of this development in the scientific instrument FXE, which makes use of these complementary X-ray tools for chemistry applications.