Modular [FeM] (M = Pd, Co, Ni, Cu) Coordination Cages.

The reaction of the simple metalloligand [FeL] [HL = 1-(4-pyridyl)butane-1,3-dione] with a variety of different M salts results in the formation of a family of heterometallic cages of formulae [FePdL]Cl (1), [FeCuL(HO)Br]Br (2), FeCuL(HO) (3), [FeNiL(SCN)Cl] (4), and [FeCoL(SCN)(HO)]Cl (5). The metallic skeleton of each cage describes a cube in which the Fe ions occupy the eight vertices and the M ions lie at the center of the six faces. Direct-current magnetic susceptibility and magnetization measurements on 3-5 reveal the presence of weak antiferromagnetic exchange between the metal ions in all three cases. Computational techniques known in theoretical nuclear physics as statistical spectroscopy, which exploit the moments of the Hamiltonian to calculate relevant thermodynamic properties, determine J = 0.10 cm for 3 and J = 0.025 cm for 4. Q-band electron paramagnetic resonance spectra of 1 reveal a significantly wider spectral width in comparison to [FeL], indicating that the magnitude of the Fe zero-field splitting is larger in the heterometallic cage than in the monomer.