A Distorted Cubic Tetranuclear Copper(II) Phosphonate Cage with a Double-Four-Ring-Type Core

The reaction of Cu2(O2CMe)4·2H2O with tert-butylphosphonic acid and 3,5-di-tert-butylpyrazole in the presence of
triethylamine leads to a high-yield synthesis of the tetranuclear compound [Cu2(3,5-t-Bu2PzH)2(t-BuPO3)2]2 (1). The
latter has a distorted cubic cage structure and its core resembles the D4R (double-four-ring) motif found in zeolites.
The phosphonate, [t-BuPO3]2-, functions as a dianionic tridentate ligand, while the pyrazole ligands are neutral
and are monodentate. The coordination geometry at each copper atom is distorted square planar with a 3O,1N
coordination environment. Magnetic measurements on 1 reveal that the χT product continuously decreases to
reach a value very close to zero at 1.8 K, indicating dominant antiferromagnetic interactions between Cu(II) ions
that leads to an S = 0 ground state. The tetranuclear cage 1 functions as a very effective artificial nuclease in the
presence of an external oxidant, magnesium monoperoxyphthalate.