A novel trisprotonated beta-dialdiminate cryptand.

The beta-dialdiminate cryptand L(4) can be isolated in the tris protonated state, [H(3)L(4)](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)] x 3 ClO(4) x MeCN.