- Solid-state synthesis of mixed trihalides via reversible absorption of dihalogens by non porous onium salts
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1,6-Bis(trimethylammonium)hexane bis(trihalides) and mixed bis(trihalides) have been synthesized by treating the corresponding dihydrated halides with molecular dihalogens under gas-solid and solution conditions. Despite the starting halides being non-porous, the trihalide syntheses occur homogeneously, in quantitative yields, and reversibly. In all cases halogen bond prevails over hydrogen bond, dihalogens substitute for the hydration water of starting halide anions and trihalides are formed. The stability of the obtained trihalides is mainly due to cooperative halogen bond and cation templation effect. Hexamethonium halides are proven effective solids for the clathration and storage of molecular dihalogens. While the starting salts are not isostructural, all the formed trihalides and mixed trihalides are isostructural.
- Meazza, Lorenzo,Marti-Rujas, Javier,Terraneo, Giancarlo,Castiglioni, Chiara,Milani, Alberto,Pilati, Tullio,Metrangolo, Pierangelo,Resnati, Giuseppe
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experimental part
p. 4427 - 4435
(2012/05/19)
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- Flexibility, association constants, and salt effects in organic ion pairs: How single bonds affect molecular recognition
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Association free energies ΔG in water from NMR shift titrations with ten ion pairs from open-chain α,ω-dianions and α,ω-dications show a dependence on ionic strength that can be fitted to the Debye-Huckel equation. In spite of the anisotropic nature of the ions, the D - H coefficient m obtained in each case is close to the theoretical value m = 4.07 for the dication/dianion combination. The ΔG values of the ten complexes and six literature values are all around 16 kJmol-1 after extrapolation to ionic strength I = 0.00, yielding a constant increment of 8kJmol-1 for each cation-anion interaction. Although the number n of flexible single bonds in the ten complexes differs from 6 to 13, the difference between the strongest and the weakest complexes (ΔG = -16.3 and - 12,6 kJ mol-1, respectively) is surprisingly small. A fairly linear correlation between ΔG and n is observed, which yields an energetic disadvantage of only ΔΔG = 0.5 kJ mo1- 1 for one single bond. This value is close to numbers obtained recently with similar hydrogen-bonded complexes in chloroform, and shows that until now the importance of conformational preorganization for effective molecular recognition has been overestimated.
- Hossain, M. Alamgir,Schneider, Hans-Joerg
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p. 1284 - 1290
(2007/10/03)
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