Self-Assembly and Properties of a Discrete Water-Soluble Prussian Blue Analogue Fe^II/Co^IIICube: Confinement of a Water Molecule in Aqueous Solution

Abstract

A novel type of water-soluble anionic cubic cages K 4 [{Co III (Me 3-Tacn)} 4 {Fe II (CN) 6 } 4 ] and Na 4 [{Co III (Me 3-Tacn)} 4 {Fe II (CN) 6 } 4 ] were prepared by means of a mechanistically designed selfassembly process between [Co(Me 3-Tacn)Cl 3 ] and M 4 [Fe II (CN) 6 ] for M = Na or K, respectively; consisting on a rate limiting outer-sphere redox step followed by a fast substitution/inner-sphere redox reaction sequence. These compounds show a remarkable stability in aqueous solution at different pH ranges, displaying neat protonation processes and a reversible oxidation with peroxodisulfate to its neutral {Fe III 4 Co III 4 } form. Furthermore, the cages behave as a robust and water-soluble molecular PrussianBlueAnalog capable of encapsulating {Na-OH 2 } + pairs and K + cations in aqueous solution, where the cubic structure of the complex is preserved. The substitution of the {Na-OH 2 } + pairs by K + is easily accomplished, and the electrochemical properties of the sodium and potassium salts of the new cages have been found dramatically dependent on the encapsulated units.

Molecular Approach to Alkali-Metal Encapsulation by a Prussian Blue Analogue FeII/CoIIICube in Aqueous Solution: A Kineticomechanistic Exchange Study

“…56 The signal at 3.87 ppm is associated with water bound to residual amounts of Na + in the building block samples, which led to formation of the already described sodium salt of the cubic structure. 45 As for the signal at 4.21 ppm, it shows a very distinct line shape that is associated with coupling to a I = 3 / 2 spin nucleus in a very symmetrical environment, as expected for a small 7 Li center ( J H–Li = 1.1 Hz). Furthermore, the chemical shift (4.21 ppm), compared with that of encapsulated {Na–OH 2 } + (3.87 ppm), is consistent with a more acidic water molecule, as expected from the higher polarizing power of the attached lithium cation.…”

“… 35 − 38 A concerted redox-triggered ligand substitution approach has led to the family of complexes indicated in Chart 1 , where cyanido ligands bridge the metal centers and the remaining coordination sites are occupied by a macrocyclic tri-, tetra-, or pentaamine (N 3 , N 4 , or N 5 ). 39 − 45 These cobalt/iron PBAs behave as discrete molecular Class II mixed-valence complexes with remarkable thermal and pH stability, as well as reversible redox reactivity; 44 , 46 − 49 this chemistry has successfully included other metals as well. 40 , 50 − 52 Potential applications of the redox properties of these complexes on inert supports have also been explored.…”

Time-Resolved Spectroscopy of Photoinduced Electron Transfer in Dinuclear and Tetranuclear Fe/Co Prussian Blue Analogues

“…[15][16][17] Subsequently, a wide variety of multinuclear molecular PBAs with CTIST character was synthesized. [18][19][20][21][22][23][24][25][26][27][28][29] Apart from larger PBA units and network systems, 30 the field also evolved towards the smallest unit cell, the dinuclear [FeCo] PBA. 31,32 The first dinuclear PBA presented by Bernhardt et al, [33][34][35] however, showed neither thermal-nor photo-induced CTIST.…”

Time-Resolved Spectroscopy of Photo-Induced Electron Transfer in Dinuclear and Tetranuclear Fe/Co Prussian Blue Analogues

“…[15][16][17] Subsequently, a wide variety of multinuclear molecular PBAs with CTIST character was synthesized. [18][19][20][21][22][23][24][25][26][27][28][29] Apart from larger PBA units and network systems, 30 the field also evolved towards the smallest unit cell, the dinuclear [FeCo] PBA. 31,32 The first dinuclear PBA presented by Bernhardt et al, [33][34][35] however, showed neither thermal-nor photo-induced CTIST.…”