The effects of different substituents and basic agents on the crystal structure of the uranyl complexes of fully deprotonated p-R-hexahomotrioxacalix[3]arene have been investigated. The trigonal equatorial coordination previously observed with R = tert-butyl and NEt₃ or DABCO as deprotonating agents, and also with H₂NBu as reported herein, appears to be changed to distorted tetragonal coordination in the cases R = methyl and NEt₃ or R = tert-butyl and NPr₃ or to distorted pentagonal coordination for R = tert-butyl and 4-methylpiperidine, passing through an intermediate case with R = tert-butyl and HNBu₂. The rare trigonal uranyl coordination observed in these compounds is likely the result of a subtle equilibrium between electronic and steric factors, the macrocyclic effect probably playing a major role, and it can be easily modified by any perturbation of these factors. Stable complexes could be investigated by ¹H NMR on dissolving the crystals obtained using secondary and tertiary amines in halogenated solvents. Ammonium ion inclusion in the aromatic cavity of an apparently C_3v symmetric complex was observed. Although less symmetric forms could not be frozen out at low temperature, the equilibration between two different types of structures was investigated.