code: def sort_members_by_importance(members):
      
      main = [x for x in members if x[0] not in config.METAL_IONS]
      ion = [x for x in members if x[0] in config.METAL_IONS]
      sorted_main = sorted(main, key=lambda x: (x[1], x[2]))
      sorted_main = sorted(main, key=lambda x: (x[1], x[2]))
      sorted_ion = sorted(ion, key=lambda x: (x[1], x[2]))
      return sorted_main + sorted_ion
docs: Sort the members of a composite ligand according to two criteria:
      1. Split up in main and ion group. Ion groups are located behind the main group.
      2. Within each group, sort by chain and position.