Top row: redshift determination from XMM-Newton spectroscopy in the kT-z plane. Red, green and blue contours trace 68, 95 and 99.9 percent confidence levels, respectively. The black error point shows the final best-fitting spectral results with associated statistical errors. Bottom row: epicemos12 (red and black points) and epn (green points) spectra. Only the data points above 2keV are shown for clarity but data down to 0.3keV are used in the spectral fitting. The line is the thermal model for the best-fitting redshift. The position of the redshifted Fe K line is marked. From left to right the figures are for sources PLCK G100.2−30.4, PLCK G277.8−51.7 and PLCK G241.2−28.7.