Protic oligozwitterions as a means of introducing strong hydrogen bonding interactions in uranyl ion coordination polymers
Résumé
The neutral, dizwitterionic dicarboxylate 1,4‐bis(carboxylatomethyl)piperazine (cmpip) is used in the solvohydrothermal synthesis of three uranyl ion complexes. Both [(UO 2 ) 2 Cl 2 (pda)(cmpip) 2 ]·2H 2 O ( 1 ) and [(UO 2 ) 2 Cl 2 (chdc)(cmpip) 2 ] ( 2 ) are mixed‐ligand complexes involving additional dianionic dicarboxylates, 1,4‐phenylenediacetate (pda 2− ), or trans ‐1,4‐cyclohexanedicarboxylate (chdc 2− ), respectively, which crystallize as two‐stranded, ladder‐like monoperiodic coordination polymers. The chains in 1 and 2 are arranged into thick layers, adjacent chains being associated through strong NH…O reciprocal hydrogen bonding of cmpip ligands. The complex [UO 2 (cmpip) 2 (H 2 O)](NO 3 )Cl·2H 2 O ( 3 ) involves only cmpip as a carboxylate donor, and it crystallizes as a diperiodic assembly with the sql topology. The four cmpip ligands bound to uranyl are located on the same side of it so as to form a deep cavity, resulting in the heavily puckered geometry of the layers. The cmpip ligands in 3 are involved in extended hydrogen bonding with other cmpip ligands and chlorine and nitrate anions. Compound 2 is nonemissive, but 1 and 3 have a photoluminescence quantum yield of 7% in the solid state, with an emission spectrum showing the usual vibronic fine structure.
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