Single crystals X-ray diffraction was performed on five crystals with nominal compositions Sr1/2Sm1/2FCl, Sr1/2Ca1/2FCl, Sr2/3Ba1/3FCl1/3Br2/3, Sr1/2Sm1/2FCl1/2Br1/2 and Sr0.6Sm0.1Ca0.3FCl. Population refinements confirm the presence of correlations between lattice constants and composition. A new correlation between the heavy halogen z value and the unit cell volume is found. Luminescence spectra of bivalent samarium in these crystals contribute to the structural characterization of these compounds.