Five- to seven-membered common-sized heterocyclic compounds containing an oxygen, sulfur, or nitrogen were synthesized by the intramolecular condensation of alpha,omega-hydroxy, mercapto, or amino alkanes, respectively, over halide cluster complexes as a thermally stable molecular solid weak acid catalyst in the gas phase at temperatures >= 150 degrees C. From omega-mercapto and omega-amino alcohols, cyclic sulfides and amines were obtained, respectively. These unimolecular reactions are thermodynamically and kinetically favored.