Incorporating Paramagnetic IrIVCl62– in H-Bonded Networks of Metal-Phosphonate Hydrate: Slow Magnetic Relaxation and Proton Conduction

Abstract

The large spin–orbital coupling and spatially extended valence orbitals of the IrIV (5d5, S = 1/2 and L = 1) are parameters responsible for its interesting magnetism in addition to the geometrical arrangements in the crystals. In order to study the effect of the Ir···Ir distance on the magnetic behavior of IrIVCl62– species, we made use of diamagnetic supramolecular hosts of CoIIICaII(notpHx) [notpH6 = C9H18N3(PO3H2)3] to accommodate the guest anion of IrIVCl62–. Controlling the protonation of the acid affects the Co:Ca ratio and the degree of hydration but does not affect its coordination or the geometry to the cobalt center. Consequently, three different salts have been isolated, [CoIII2CaII2(notpH2)2(H2O)8](IrIVCl6)·2H2O at pH 3.5 (1), [CoIII2CaII(notpH3)2(H2O)2](IrIVCl6)·4H2O at pH 2.5 (2), and [CoIII2(notpH4)2](IrIVCl6)·6H2O at pH 1.7 (3). The distance between the IrIVCl62– anions varies in the sequence 3 < 1 < 2. Magnetic studies reveal that only 2 exhibits slow magnetic relaxation associated with IrIVCl62–, which correlates with the large Ir···Ir distance (9.428 Å) and the absence of a halogen bond between neighboring IrIVCl62– (Cl···Cl > 4.941 Å). Furthermore, the different degree of protonation in 1–3 also poses influences on their proton conductivities which increase with the protonation of the phosphonate groups under 95% RH and 25 °C.