Synthesis and Characterization of Mixed‐Valent Manganese Phosphonate Cage Complexes

The reaction of phenylphosphonic acid (PhPO 3 H 2 ) with the mixed‐valent basic oxo‐centered manganese triangle [Mn 3 O(O 2 CCMe 3 ) 6 (py) 3 ] ( 1 ; where p y =pyridine) in the presence of a suitable base gives four different manganese clusters depending on the identity of the base. The syntheses and structural characterization of [Mn 18 (μ 3 ‐O) 8 (PhPO 3 ) 14 (O 2 CCMe 3 ) 12 (py) 6 (H 2 O) 2 ] ( 2 ), [Mn 7 (μ 3 ‐O) 3 (O 3 PPh) 3 (O 2 CCMe 3 ) 8 (py) 3 ] ( 3 ), [Mn 9 Na(μ 3 ‐O) 4 (μ 4 ‐O) 2 (O 3 PPh) 2 (O 2 CCMe 3 ) 12 (H 2 O) 2 (H 2 O) 0.67 (Py) 0.33 ] ( 4 ), and [Mn 13 (μ 3 ‐O) 8 (OMe) 8 (O 3 PPh) 4 (O 2 CCMe 3 ) 10 ] ( 5 ) are described. Complexes 4 and 5 are homovalent Mn III cages, while 2 and 3 contain divalent, trivalent, and/or tetravalent ions. All the manganese centers are valence‐localized, the octahedral Mn III sites being recognizable by marked Jahn–Teller distortions. The magnetic properties of compounds 2 – 5 have been investigated in the polycrystalline state by magnetic susceptibility and high‐field magnetization measurements, which reveal that spin ground states vary from 0≤ S ≥8. AC susceptibility measurements performed on 4 and 5 , in the 1.6–10.0 K ranges show the presence of out of AC susceptibility signal ( χ M ′′) for 4 , and an effective energy barrier ( U eff ) for the re‐orientation of the magnetization is found to be 17 K, but for 5 , the χ M ′′ maximum is found to be below 1.5 K.