Expanded Prussian Blue Analogues Incorporating [Re₆Se₈(CN)₆]^3-/4- Clusters:  Adjusting Porosity via Charge Balance

Abstract

Face-capped octahedral [Re(6)Se(8)(CN)(6)](3-/4-) clusters are used in place of octahedral [M(CN)(6)](3-/4-) complexes for the synthesis of microporous Prussian blue type solids with adjustable porosity. The reaction between [Fe(H(2)O)(6)](3+) and [Re(6)Se(8)(CN)(6)](4-) in aqueous solution yields, upon heating, Fe(4)[Re(6)Se(8)(CN)(6)](3).36H(2)O (4). A single-crystal X-ray analysis confirms the structure of 4 to be a direct expansion of Prussian blue (Fe(4)[Fe(CN)(6)](3).14H(2)O), with [Re(6)Se(8)(CN)(6)](4-) clusters connected through octahedral Fe(3+) ions in a cubic three-dimensional framework. As in Prussian blue, one out of every four hexacyanide units is missing from the structure, creating sizable, water-filled cavities within the neutral framework. Oxidation of (Bu(4)N)(4)[Re(6)Se(8)(CN)(6)] (1) with iodine in methanol produces (Bu(4)N)(3)[Re(6)Se(8)(CN)(6)] (2), which is then metathesized to give the water-soluble salt Na(3)[Re(6)Se(8)(CN)(6)] (3). Reaction of [Co(H(2)O)(6)](2+) or [Ni(H(2)O)(6)](2+) with 3 in aqueous solution affords Co(3)[Re(6)Se(8)(CN)(6)](2).25H(2)O (5) or Ni(3)[Re(6)Se(8)(CN)(6)](2).33H(2)O (6). Powder X-ray diffraction data show these compounds to adopt structures based on the same cubic framework present in 4, but with one out of every three cluster hexacyanide units missing as a consequence of charge balance. In contrast, reaction of [Ga(H(2)O)(6)](3+) with 3 gives Ga[Re(6)Se(8)(CN)(6)].6H(2)O (7), wherein charge balance dictates a fully occupied cubic framework enclosing much smaller cavities. The expanded Prussian blue analogues 4-7 can be fully dehydrated, and retain their crystallinity with extended heating at 250 degrees C. Consistent with the trend in the frequency of framework vacancies, dinitrogen sorption isotherms show porosity to increase along the series of representative compounds 7, Ga(4)[Re(6)Se(8)(CN)(6)](3).38H(2)O, and 6. Furthermore, all of these phases display a significantly higher sorption capacity and surface area than observed in dehydrated Prussian blue. Despite incorporating paramagnetic [Re(6)Se(8)(CN)(6)](3-) clusters, no evidence for magnetic ordering in compound 6 is apparent at temperatures down to 5 K. Reactions related to those employed in preparing compounds 4-6, but carried out at lower pH, produce the isostructural phases H[cis-M(H(2)O)(2)][Re(6)Se(8)(CN)(6)].2H(2)O (M = Fe (8), Co (9), Ni (10)). The crystal structure of 8 reveals a densely packed three-dimensional framework in which [Re(6)Se(8)(CN)(6)](4-) clusters are interlinked through a combination of protons and Fe(3+) ions.

Syntheses, Crystal Structures and Adsorption Properties of Ultramicroporous Coordination Polymers Constructed from Hexafluorosilicate Ions and Pyrazine

“…For separation and purification of smaller gas molecules, such micropores need to be further narrowed to become ultramicropores, as in Prussian blue (M(CN) 2 ) analogues. [32,33] When we focus on SiF 6 2--containing coordination compounds, [M(SiF 6 )(4,4Ј-bpy) 2 ] n (M = Zn 2+ , Cu 2+ ), [31,[34][35][36] which are compounds that can be regarded as having been generated from square-grid coordination polymers that are cross-linked by µ-SiF 6 anions, replacing 4,4Ј-bpy by pyrazine (pyz) would produce the required ultramicropores. Herein, we show the synthesis and characterization of ultramicroporous coordination polymers with formulae [M(SiF 6 )(pyz) 2 ] n employed for gas and vapour adsorption studies and especially H 2 storage properties.…”

SPIN-ORBIT AND SOLVENT EFFECTS IN THE LUMINESCENT [Re6Q8(NCS)6]4-, Q=S, Se, Te CLUSTERS: MOLECULAR SENSORS AND MOLECULAR DEVICES

“…Moreover, the synthetic versatility of the [Re 6 Q 8 ] 2+ cluster core has allowed the synthesis of extended new porous materials that can be used as molecular sieves, or used as starting material for designing versatile chemical sensors for the detection of a large variety of volatile organic contaminants, (VOC), because due to the labile nature of the apical ligands they get substituted by VOC ligands, thus inducing an immediate color change at very low VOC concentrations, please see Scheme 1 [5][6][7][8].…”

“…The chemistry of the hexarhenium (III) chalcogenide cluster complexes is particularly attractive due to their synthetic versatility, photoluminescent and redox active properties [2][3][4][5][6][7][8][16][17][18][19][20][21][22][23]. The hexarhenium (III) chalcogenide clusters, the hexamolybdenum halide clusters and the hexatungsten halide cluster [9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25] complexes are characterized by showing long emission lifetimes (ms), electronic absorption spectra which are mostly characterized by intense LMCT transitions, emission spectra which arises from closely spaced excited states localized on the [M 6 (Q,X) 8 ] q+ cluster core with significant metal and bridging ligand content, and, all the cluster undergoes reversible oxidation process at a remarkable low potential, indicating that it can easily be switched between two stable oxidation states. In all cases we predicted that the terminal iodide ligands are the most kinetically labile and are the molecular precursor for functionalizing the hexanuclear clusters [19][20][21][22][23][24][25].…”

[Re6(μ3-Se)8]2+ Core-Containing Cluster Complexes with Isonicotinic Acid: Synthesis, Structural Characterization, and Hydrogen-Bonded Assemblies

“…cluster core have been reported [13,14]. Several of these compounds utilize [Re 6 (l 3 -Se) 8 (CN) 6 ] 4-as a linker to build polymeric arrays with direct coordination to secondary metal ions [15][16][17][18][19][20][21][22][23]. Other efforts involve incorporating cluster systems into polymers [24], nanoparticles [25], self-assembly structures [26][27][28], and surfaces [29], all for the purpose of integrating the red/nearinfrared luminescence and redox properties of the cluster for functional materials.…”