Aluminum species in AlCl3-arene and AlCl3-CuCl-arene solutions (including benzene, toluene, o-xylene, m-xylene, p-xylene, and mesitylene) were investigated using Al-27 NMR and infrared (IR) spectroscopy. The AlCl3 center dot arene and Al2Cl6 center dot arene complexes were demonstrated experimentally. AlCl3 could not coordinate with benzene and toluene at a low temperature (40 degrees C) but could form complexes at a high temperature (80 degrees C). AlCl3 could coordinate with xylene and mesitylene to form Al2Cl6 center dot arene complexes at both low and high temperatures (40 and 80 degrees C). As for AlCl3-CuCl-arene solutions with a molar ratio of 1:1:2, two signals were observed in Al-27 NMR spectra. The signal at around 101 ppm was assigned to CuAlCl4 center dot 2arene complexes, and the other signal at around 96 ppm belonged to AlCl3 center dot arene complexes. The characteristic peaks of AlCl3-CuCl-arene solutions in IR spectra moved toward the low field due to the strong pi-back-bonding. The CuAlCl4 center dot 2arene complexes would convert to CuAl2Cl7 center dot 2arene complexes with a further increase in AlCl3 content when the molar ratio of AlCl3/CuCl exceeded 1. The synthesis mechanism of AlCl3-CuCl-arene solutions was analyzed by in situ Fourier transform IR (FTIR) spectroscopy. Three reaction pathways originating from different aluminum species were proposed.