Abstract
In order to demonstrate the role of the fluorination and some solvents in the structural organization of the Ag(I) coordination polymers with β-diketonate ligands (R1C(O)CαHC(O)R2)− we synthesized a series of the compounds containing tfac- (R1 = CH3, R2 = CF3) and pfpac- (R1 = CH3, R2 = C2F5) anions. Solvent-free [Ag(L)]∞ (L = tfac 1, pfpac 2) compounds and the corresponding acetonitrile and toluene adducts have been characterized by elemental analysis and/or NMR, IR and single-crystal XRD. This series includes five new coordination polymers. Compound 1 is a 3D coordination framework based on Ag–Ochelate/bridge, Ag–Cα bonds, and argentophilic interactions. An increase in the fluorinated group leads to a chain coordination polymer 2 of an unusual structural organization. These chains can be represented as a “DNA-type”, where two intertwined helices based on Ag–Ochelate and Ag–Cα bonds are connected through Ag–Obridge ones. Two structural types of chain coordination polymers, [Ag(tfac)(CH3CN)] and [Ag2(L)2(solvent)], have been revealed for the adducts. The latter structural type differs significantly from the previously studied toluene and acetonitrile adducts of fluorinated Ag(I) β-diketonates of the same stoichiometry. Thermal analysis in helium showed that both 1 and 2 decompose to metallic silver with the compound of pfpac-ligand being slightly more stable.
Highlights
Introduction β-Diketonate ligands (R1C(O)CαRC(O)R2)− are widely demanded building blocks in coordination chemistry, which are distinguished by a chelating effect and internal conjugation, providing stability, and their great structural versatility by their varying terminal groups (R1 and R2) and the substituent at the methine carbon atom (Cα) [1,2,3,4]
We have investigated the effect of a fluorinated substituent (CF3/C2F5) and N-donor (CH3CN) and aromatic solvents on the structural and thermal properties of this class of the silver compounds
The results obtained were analyzed in comparison with a series of related, fluorinated Ag (I) β-diketonates and their acetonitrile and toluene adducts
Summary
All reagents and solvents were commercially available. For synthesis under ambient conditions no additional purification was performed. The synthesis in air was performed for 1w; the solvent volume was reduced to prevent product dissolution. Adducts with acetonitrile and toluene were obtained by recrystallization of Ag(I) aqua-β-diketonates 1w and 2w from the corresponding solvents under ambient conditions. The products were formed as white powders and corresponded to stoichiometry [Ag2(L)2Q]∞ (Q = CH3CN, toluene; L = tfac, pfpac). Ag2(tfac)2(CH3CN), 1H NMR spectrum (DMSO-d6, 2.50 ppm): δ 5.14 (br s, 1H, Cα–H), 2.07 (s, (3H) × 0.5, –CH3, CH3CN), 1.98 (s, 3H, –CH3, tfac). [Ag2(pfpac)2(CH3CN)]∞ 2a, 1H NMR spectrum (DMSO-d6, 2.50 ppm): δ 5.06 (br s, 1H, Cα–H), 2.07 (s, (3H) × 0.5, –CH3, CH3CN), 2.02 (s, 3H, –CH3, pfpac). The crystals of the adducts suitable for single-crystal XRD were obtained by slow evaporation of the corresponding solvents at 5 ◦C. The stoichiometry of the crystals corresponded to powder samples, except with [Ag(tfac)(CH3CN)]∞ 1a
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