Structure of 11,14,27,30,35,38,43,46-octaoxa-1,8,17,24-tetraazapentacyclo[22.8.8.88,17.23,6.219,22]dopentaconta-3,5,19,21,49,51-hexaene, C40H64N4O8, a tricyclic macrocycle featuring two [18]-N2O4 binding subunits and two benzene bridges