Synthesis, structural characterisation and magnetic studies of polymetallic iron phosphonate cages

Abstract

Four new polymetallic iron(III) phosphonate cages have been made and structurally characterised. These are an octanuclear cage [Fe₈O₃(OH)₂(O₂C^tBu)₁₁(PhCH₂PO₃)₃(py)₃], a decanuclear cage [Fe₁₀O₂(OH)₈(O₂C^tBu)₁₀(PhCH₂PO₃)₄(pip)₂], a heterometallic cage [Fe₆Li₅(μ₃-O)₂(^tBuPO₃)₆(O₂C^tBu)₈(MeOH)₂(Py)₄] and a tridecanuclear cage [Et₃NH]₂[Fe₁₃(μ₃-O)₃(μ₂-OH)₇(^tBuPO₃)₇(Me₃CCO₂)₁₄(H₂O)] (pip = piperidine, py = pyridine). Magnetic studies of the first three compounds show anti-ferromagnetic exchange between the iron(III) centers leading to diamagnetic ground states for the homometallic cages. For the heterometallic cage, the six Fe(III) centers are arranged in two triangles, and each triangle has an S = 1/2 spin ground state.