X-ray luminosity in the 0.1–2.4 keV band for the clusters in the sample here analyzed. Different symbols and colors refer to different sub-samples. Clusters that host a radio halo (red diamonds); clusters where a radio halo has not been detected so far, but with signature of on-going merger according to the literature (cyan triangles), other clusters (squares). The cluster A1650, whose merging state is debated, is signed with a blue asterisk.