Infrared spectra (500–195 cm.–1) in di-isopropyl ether show bands due to the complex acids, HMX4, formed on solvent extraction of Ga3+, In3+, and Tl3+ from HCl and HBr solutions, confirming previous Raman deductions. The tetrahalogeno-ions have Td symmetry with the v3 frequencies: GaCl4–= 374; GaBr4–= 274; InCl4–= 333; InBr4–= 233; TlCl4–= 293; TlBr4–= 197 cm.–1. The same frequencies are found in crystalline tetramethylammonium salts of the bromo-ions and GaCl4– but the indium and thallium chloride complex salts have different spectra attributed to pentachloro-ions.