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Dynamics and Counterion‐Dependence of the Structures of Weakly Bound Ag + –P 4 S 3 Complexes
Author(s) -
Raabe Ines,
Antonijevic Sasa,
Krossing Ingo
Publication year - 2007
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200601885
Subject(s) - counterion , alkoxide , cationic polymerization , chemistry , ion , crystallography , adduct , molecular dynamics , salt (chemistry) , stereochemistry , computational chemistry , polymer chemistry , organic chemistry , catalysis
In an earlier publication ( J. Am. Chem. Soc. 2002 , 124 , 7111) we showed that polymeric cationic [Ag(P 4 S 3 ) n ] + complexes ( n =1, 2) are accessible if partnered with a suitable weakly coordinating counterion of the type [Al(OR F ) 4 ] − (OR F : poly‐ or perfluorinated alkoxide). The present work addresses the following questions that could not be answered in the initial report: How many P 4 S 3 cages can be bound to a Ag + ion? Why are these complexes completely dynamic in solution in the 31 P NMR experiments? Can these dynamics be frozen out in a low‐temperature 31 P MAS NMR experiment? What are the principal binding sites of the P 4 S 3 cage towards the Ag + ion? What are likely other isomers on the [Ag(P 4 S 3 ) n ] + potential energy surface? Counterion influence: Reactions of P 4 S 3 with Ag[Al{OC(CH 3 )(CF 3 ) 2 } 4 ] (Ag[hftb]) and Ag[{(CF 3 ) 3 CO} 3 Al‐F‐Al{OC(CF 3 ) 3 )} 3 ] (Ag[al‐f‐al]) gave [(P 4 S 3 )Ag[hftb]] ∞ ( 7 ) as a molecular species, whereas [Ag 2 (P 4 S 3 ) 6 ] 2+ [al‐f‐al] − 2 ( 8 ) is an isolated 2:1 salt. We suggest that a maximum of three P 4 S 3 cages may be bound on average to an Ag + ion. Only isolated dimeric dications are formed with the largest cation, but polymeric species are obtained with all other smaller aluminates. Thermodynamic Born–Haber cycles, DFT calculations, as well as solution NMR and ESI mass spectrometry indicate that 8 exhibits an equilibrium between the dication [Ag 2 (P 4 S 3 ) 6 ] 2+ (in the solid state) and two [Ag(P 4 S 3 ) 3 ] + monocations (in the gas phase and in solution). Dynamics: 31 P MAS NMR spectroscopy showed these solid adducts to be highly dynamic, to an extent that the 2 J P,P coupling within the cages could be resolved ( J ‐res experiment). This is supported by DFT calculations, which show that the extended PES of [Ag(P 4 S 3 ) n ] + ( n =1–3) and [Ag 2 (P 4 S 3 ) 2 ] + is very flat. The structures of α‐ and γ‐P 4 S 3 were redetermined. Their variable‐temperature 31 P MAS NMR spectra are discussed jointly with those of all four currently known [Ag(P 4 S 3 ) n ] + adducts with n =1, 2, and 3.