Role of N-Donor Sterics on the Coordination Environment and Dimensionality of Uranyl Thiophenedicarboxylate Coordination Polymers

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• 作者：Sonia G. Thangavelu ; Ray J. Butcher ; Christopher L. Cahill
• 刊名：Crystal Growth & Design
• 出版年：2015
• 出版时间：July 1, 2015
• 年：2015
• 卷：15
• 期：7
• 页码：3481-3492
• 全文大小：736K
• ISSN：1528-7505

文摘

Thiophene 2,5-dicarboxylic acid (TDC) was reacted with uranyl acetate dihydrate and one (or none) of six N-donor chelating ligands (2,2鈥?bipyridine (BPY), 4,4鈥?dimethyl-2,2鈥?bipyridine (4-MeBPY), 5,5鈥?dimethyl-2,2鈥?bipyridine (5-MeBPY), 6,6鈥?dimethyl-2,2鈥?bipyridine (6-MeBPY), 4,4鈥?6,6鈥?tetramethyl-2,2鈥?bipyridine (4,6-MeBPY), and tetrakis(2-pyridyl)pyrazine (TPPZ) to result in the crystallization of seven uranyl coordination polymers, which were characterized by their crystal structures and luminescence properties. The seven coordination polymers, Na₂[(UO₂)₂(C₆H₂O₄S)₃]路4H₂O (1), [(UO₂)₄(C₆H₂O₄S)₅(C₁₀H₈N₂)₂]路C₁₀H₁₀N₂路3H₂O (2), [(UO₂)(C₆H₂O₄S)(C₁₂H₁₂N₃)] (3), [(UO₂)(C₆H₂O₄S)(C₁₂H₁₂N₃)]路H₂O (4), [(UO₂)₂(C₆H₂O₄S)₃]路(C₁₂H₁₄N₂)路5H₂O (5), [(UO₂)₃(CH₃CO₂)(C₆H₂O₄S)₄](C₁₄H₁₇N₂)₃路(C₁₄H₁₆N₂)路H₂O (6), and [(UO₂)₂(C₆H₂O₄S)₃](C₂₄H₁₈N₆) (7), consist of either uranyl hexagonal bipyramidal or pentagonal bipyramidal coordination geometries. In all structures, structural variations in the local and global structures of 1鈥?b>7 are influenced by the positions (or number) of methyl groups or pyridyl rings on the N-donor species, thus resulting in a wide diversity of structures ranging from single chains, double chains, or 2-D sheets. Direct coordination of N-donor ligands to uranyl centers is observed in the chain structures of 2鈥?b>4 using BPY, 4-MeBPY, and 5-MeBPY, whereas the N-donor species participate as guests (as either neutral or charge balancing species) in the chain and sheet structures of 5鈥?b>7 using 6-MeBPY, 4,6-MeBPY, and TPPZ, respectively. Compound 1 is the only structure that does not contain any N-donor ligands and thus crystallizes as a 2-D interpenetrating sheet. The luminescent properties of 1鈥?b>7 are influenced by the direct coordination or noncoordination of N-donor species to uranyl centers. Compounds 2鈥?b>4 exhibit typical UO₂²⁺ emission upon direct coordination of N-donors, but its absence is observed in 1, 5, 6, and 7, when N-donor species participate as guest molecules. These results suggest that direct coordination of N-donor ligands participate as chromophores, thus resulting in possible UO₂²⁺ sensitization. The lack of emission in 1, 5, 6, and 7 may be explained by the extended conjugation of the TDC ligands within their structures.