Dynamics and counterion-dependence of the structures of weakly bound Ag+-P4S3 complexes.

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]](infinity) (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 alpha- and gamma-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.