  77Se and 87Rb nuclear magnetic resonance (NMR) experiments on Rb0.74Fe1.6Se2
reveal clearly distinct spectra originating from a majority antiferromagnetic
(AF) and a minority metallic-superconducting (SC) phase. The very narrow NMR
line of the SC phase evidences the absence of Fe vacancies and any trace of AF
order. The Rb content of the SC phase is deduced from intensity measurements
identifying Rb0.3(1)Fe2Se2 as the actual composition of the SC fraction. The
resulting estimate of 0:15 electrons/Fe brings this class of superconductors
245 family closer to the other Fe-based superconductor families.
