Incorporating Paramagnetic Ir^IVCl₆^2– 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 Ir IV (5d 5 , 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 Ir IV Cl 6 2− species, we made use of diamagnetic supramolecular hosts of Co III Ca II (notpH x ) [notpH 6 = C 9 H 18 N 3 (PO 3 H 2 ) 3 ] to accommodate the guest anion of Ir IV Cl 6 2− . 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, [Co III 2 Ca II 2 (notpH 2 ) 2 (H 2 O) 8 ]-(Ir IV Cl 6 )•2H 2 O at pH 3.5 (1), [Co III 2 Ca II (notpH 3 ) 2 (H 2 O) 2 ](Ir IV Cl 6 )•4H 2 O at pH 2.5 (2), and [Co III 2 (notpH 4 ) 2 ](Ir IV Cl 6 )•6H 2 O at pH 1. 7 (3). The distance between the Ir IV Cl 6 2− anions varies in the sequence 3 < 1 < 2. Magnetic studies reveal that only 2 exhibits slow magnetic relaxation associated with Ir IV Cl 6 2− , which correlates with the large Ir•••Ir distance (9.428 Å) and the absence of a halogen bond between neighboring Ir IV Cl 6 2− (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.

A new family of one-dimensional bromo-bridged Ir(iv)–Cu(ii) complexes based on the hexabromoiridate(iv) metalloligand

“…0.35 cm 3 mol −1 K, which is as previously observed for one isolated Ir IV (5d 5 ion with t 2g 5 electronic configuration and S eff = 1/2). 5–7,11 Upon cooling, the χ M T value slowly decreases with decreasing temperature to approximately ca . 20 K, then it decreases faster, reaching a minimum value of ca .…”

“…Iridium molecular systems are currently being investigated due in large part to the potential technological applications that they exhibit in several research fields, such as catalysis, imaging, sensing or magnetism. 1–10 Nevertheless, it is worth noting that Ir IV complexes remain largely unexplored when compared to other oxidation states of this paramagnetic metal ion. 4–7…”

“…1–10 Nevertheless, it is worth noting that Ir IV complexes remain largely unexplored when compared to other oxidation states of this paramagnetic metal ion. 4–7…”

“…In particular, recent interest is being paid to the synthesis and investigation of compounds based on Ir IV metal ion (5d 5 ion with S = 1/2 and L = 1) in the field of molecular magnetism. 5–7,10,11 Thus, sodium hexachloroiridate salts (with a different degree of hydration) have been studied, which behave as spin-canted systems with short Cl⋯Cl interactions and magnetic ordering temperatures covering the range 2.7–7.4 K. 5 When the sodium cation is replaced by a diamagnetic metal-phosphonate (with a different degree of protonation), thus keeping the [IrCl 6 ] 2− anions more separate from each other, single-ion magnet (SIM) behaviour and proton conductivity are observed. 6 Besides, the Ir IV complexes of general formula (PPh 4 ) 2 [IrX 6 ] (X = F and Cl; PPh 4 + = tetraphenylphosphonium cation), both of them showing SIM behaviour, have been proposed as suitable models to explain the physics of some oxido-iridates.…”

“…The hexahaloiridate( iv ) salts, [IrX 6 ] 2− (X = F, Cl and Br), have been studied during several decades. 1–12 Nevertheless, in comparison to other highly anisotropic 5d metal ions, 13–23 the use of the [IrX 6 ] 2− anions as metalloligands towards paramagnetic metal ions has been barely explored.…”