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(P₄S₃)_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 P₄S₃ cages can be bound to a Ag⁺ ion? Why are these complexes completely dynamic in solution in the ³¹P NMR experiments? Can these dynamics be frozen out in a low‐temperature ³¹P MAS NMR experiment? What are the principal binding sites of the P₄S₃ cage towards the Ag⁺ ion? What are likely other isomers on the Ag(P₄S₃)_n]⁺ potential energy surface? Counterion influence: Reactions of P₄S₃ with AgAl{OC(CH₃)(CF₃)₂}₄] (Aghftb]) and Ag{(CF₃)₃CO}₃Al‐F‐Al{OC(CF₃)₃)}₃] (Agal‐f‐al]) gave (P₄S₃)Aghftb]]_∞ ( 7 ) as a molecular species, whereas Ag₂(P₄S₃)₆]²⁺al‐f‐al]^?₂ ( 8 ) is an isolated 2:1 salt. We suggest that a maximum of three P₄S₃ 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 Ag₂(P₄S₃)₆]²⁺ (in the solid state) and two Ag(P₄S₃)₃]⁺ monocations (in the gas phase and in solution). Dynamics: ³¹P MAS NMR spectroscopy showed these solid adducts to be highly dynamic, to an extent that the ²J_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(P₄S₃)_n]⁺ (n=1–3) and Ag₂(P₄S₃)₂]⁺ is very flat. The structures of α‐ and γ‐P₄S₃ were redetermined. Their variable‐temperature ³¹P MAS NMR spectra are discussed jointly with those of all four currently known Ag(P₄S₃)_n]⁺ adducts with n=1, 2, and 3.