The crystal structures of the complexes formed by benzo-18-crown-6 with barium perchlorate and with strontium perchlorate, bisperchloratobisaquo(6, 7, 9, 10, 12, 13, 15, 16, 18, 19 decahydro benzo [b]-1, 4, 7, 10, 13, 16 hexaoxacyclooctadecin)- barium and trisaquo(6, 7, 9, 10, 12, 13, 15, 16, 18, 19 decahydrobenzo [b]-1, 4, 7, 10, 13, 16 hexaoxacyclooctadecin)strontium diperchlorate