The topochemical deintercalation of Na+ ions from solid NaFeAs at room temperature in THF with iodine yields the superconducting phase Na1-yFe2-xAs2 (T-c approximate to 11 K). This metastable iron arsenide decomposes at 120 degrees C and is not accessible by high-temperature solid-state synthesis. X-ray powder diffraction confirms the ThCr2Si2-type structure, but reveals very small coherently scattering domains with a mean composition Na0.9(2)Fe1.7(1)As2. HRTEM investigations show crystalline as well as strongly distorted areas with planar defects. The latter are probably due to sodium loss and disorder which is also detected by Na-23 solid state NMR. The Fe-57-Mossbauer spectrum of Na1-yFe2-xAs2 shows one type of iron atoms in tetrahedral coordination. All results point to one crystallographic phase with very small domains due to fluctuations of the chemical composition. From electronic reasons we suggest the superconducting phase is presumably NaFe2As2 in the ordered fractions of the sample.