The self-assembly process involving the dianion of trimesic acid (Htrim(2-)) and {Cu(tmen)}(2+) templating cations (tmen = N,N,N',N'-tetramethylethylenediamine) affords a new metallacalixarene, [Cu-4(tmen)(4)(Htrim)(4)]center dot nH(2)O. The packing of the cyclic molecules in the crystal generates channels that are fitted by water molecules. The dehydration-rehydration process of the crystals was found to be reversible.