A novel trisprotonated beta-dialdiminate cryptand

The beta-dialdiminate cryptand L-4 can be isolated in the tris protonated state, [H3L4](3+), from the condensation of malonaldehyde (generated in situ from its tetraacetal derivative) with tris-2-aminoethylamine (tren) in [3 + 2] mode. The cryptate cannot be deprotonated under aqueous conditions, but the neutral cryptand can be made by treatment with KOH in dry methanol. This cryptand is water-sensitive, but may be treated with copper salts under anhydrous conditions to generate highly insoluble copper(II) derivatives. The reduced form of the cryptand L-5 can be isolated upon borohydride reduction, and used to make dicopper mu-hydroxo cryptates, where strong interaction between the pair of encapsulated paramagnetic cations leads to effective magnetic silence. Crystal structures of L-4 in three of its tris protonated salts and of the solvated neutral ligand L-4 are presented, together with that of a mu-hydroxo dicopper(II) cryptate of the fully reduced cryptand, [Cu-2(OH)L-5]center dot 3ClO(4)center dot MeCN.