| Abstract
| - A technique for increasing the porosity in solid structures by replacing octahedral metal ions withhexanuclear cluster cores is extended with the expansion of the ion-exchange material Na2Zn3[Fe(CN)6]2·9H2O. At high relative cluster concentrations, the reaction between [Zn(H2O)6]2+ and Na4[Re6Se8(CN)6] producesNa2Zn3[Re6Se8(CN)6]2·24H2O (1), a compound exhibiting a porous three-dimensional framework isotypic withthat of Na2Zn3[Fe(CN)6]2·9H2O. Its framework is characterized by hexagonal bipyramidal cages, each enclosingtwo Na+ ions and 24 water molecules in a volume of 1340 Å3more than triple the volume of the cages inthe original structure. The expanded cavities and framework openings in compound 1 are shown to facilitateabsorption of larger cationic complexes, specifically [M(H2O)6]n+ (M = Mg2+, Cr3+, Mn2+, Ni2+, Zn2+) and[Cr(en)3]3+, via exchange for the Na+ ions. Indeed, when the preparation of 1 is attempted using a slightexcess of the zinc reactant, [Zn(H2O)6]2+ incorporates instead of Na+, leading to direct formation of the ion-exchanged compound [Zn(H2O)6]Zn3[Re6Se8(CN)6]2·18H2O (2). The crystal structure of 2 reveals the [Zn(H2O)6]2+ complexes to reside at the exact center of the hexagonal bipyramidal cages. With prolonged exposureto air, compound 1 and its ion-exchanged variants undergo a color change from orange to green, which isattributed to the one-electron oxidation of the [Re6Se8]2+ cluster cores in the solid framework. In a furtherparallel with ferrocyanide chemistry, the reaction between [Zn(H2O)6]2+ and Na4[Re6Se8(CN)6] at low relativecluster concentrations is found to yield [Zn(H2O)]2[Re6Se8CN)6]·13H2O (3), a phase exhibiting a two-dimensionalframework structure isotypic with that of [Zn(H2O)]2[Fe(CN)6]·0.5H2O.
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