In situ X-ray absorption spectroscopy was performed at beamline 11-2 at SSRL. The precursor mixture was packed into a quartz capillary, which was placed between two coil heaters. The typical temperature profile was followed, but the maximum temperature for this experiment was 800 °C rather than 900 °C as in all other heating experiments. Fluorescence spectra were collected. Calibration and detuning were performed in the same manner as ex situ experiments. Additional details of the spectroscopic analysis are available in the SI.