Single-crystalline tetrafluoridochlorates(III) A[ClF4] (A = K, Rb, Cs) were synthesized from solvolysis reactions of alkali metal fluorides in liquid chlorine trifluoride. The structures were examined by means of single-crystal X-ray diffraction. K[ClF4] crystallizes in the K[BrF4] structure type, whereas the Rb and Cs compounds crystallize in the Li[AuF4] structure type. The compounds were further characterized by Raman and IR spectroscopy. Solid-state quantum-chemical calculations with hybrid density functional methods reproduced the experimental structures and enabled the interpretation of the experimental Raman and IR spectra.