ABSTRACT
A series of six coordination polymers based on octahedral cluster anions [Re6Q8(CN)6]4- (Q = S or Se) and Ag+ cations coordinated by bipyridine analogs were synthesized under solvothermal conditions. Their structures have been characterized by single crystal X-ray diffraction. Compounds 1 and 2 described by the general formula [{Ag(phen)}4Re6Q8(CN)6] (Q = Se (1), S (2); phen = 1,10-phenanthroline) exhibit layered structures assembled into a supramolecular network by CH π contacts. At the same time, compounds [{Ag(bipym)}2Ag2Re6Se8(CN)6] (bipym = 2,2'-bipyrimidine) (3), [{Ag2(bipy)}Ag2Re6Se8(CN)6]·CH3CN (bipy = 4,4'-bipyridine) (4) and [{Ag(dpbp)}4Re6Q8(CN)6]·2H2O·2CH3CN (Q = Se (5), S (6); dpbp = 4,4'-Di(4-pyridyl)biphenyl)) evince framework structures. In 1, 2, 5 and 6 weak Agâ¯Ag interactions are observed. All the compounds show luminescence in the red region. The luminescence quantum yields and lifetimes were found to be notably higher than those for most of the coordination polymers based on the octahedral rhenium cluster complexes.
ABSTRACT
The redox-active rhenium octahedral cluster unit [Re6Se8(CN)6]4- was combined with Gd3+ ions and dicarboxylate linkers in novel types of metal-organic frameworks (MOFs) that display a set of functional properties. The hydrolytically stable complexes [{Gd(H2O)3}2(L)Re6Se8(CN)6]·nH2O (1, L = furan-2,5-dicarboxylate, fdc; 2, L = thiophene-2,5-dicarboxylate, tdc) exhibit a 3D framework of trigonal symmetry where 1D chains of [{Gd(H2O)3}2(L)]4+ are connected by [Re6Se8(CN)6]4- clusters. Frameworks contain spacious channels filled with H2O. Solvent molecules can be easily removed under vacuum to produce permanently porous solids with high volumetric CO2 uptake and remarkable CO2/N2 selectivity at room temperature. The frameworks demonstrate an ability for reversible redox transformations of the cluster fragment. The orange powders of compounds 1 and 2 react with Br2, yielding dark-green powders of [{Gd(H2O)3}2(L)Re6Se8(CN)6]Br·nH2O (3, L = fdc; 4, L = tdc). Compounds 3 and 4 are isostructural with 1 and 2 and also have permanently porous frameworks but display different optical, magnetic, and sorption properties. In particular, oxidation of the cluster fragment "switches off" its luminescence in the red region, and the incorporation of Br- leads to a decrease of the solvent-accessible volume in the channels of 3 and 4. Finally, the green powders of 3 and 4 can be reduced back to the orange powders of 1 and 2 by reaction with hydrazine, thus displaying a rare ability for fully reversible chemical redox transitions. Compounds 1-4 are mentioned as a new class of redox-active cluster-based MOFs with potential usage as multifunctional materials for gas separation and chemical contamination sensors.
