Synthesis and crystal structure of tetra-kis-(perfluoro-benzo-nitrile)-silver(I) tetra-kis-(perfluoro-tert-but-oxy)aluminate(1-): a perfluorinated silver(I) nitrile cation with a perfluorinated weakly coordinating anion.

The title compound, [Ag(C6F5CN)4][Al{OC(CF3)3}4], was obtained by reaction of Ag[Al(OC(CF3)3)4] with excess perfluoro-benzo-nitrile. The crystals belong to the chiral space group P21 with Z' = 2, containing two independent [Ag(C6F5CN)4]+ cations and two [Al(OC(CF3)3)4]- anions in the asymmetric unit. Each AgI centre is four-coordinate and adopts a distorted tetra-hedral geometry. One of the nitrile ligands in both AgI centres has a noticeably longer Ag-N distance [2.383 (8) and 2.371 (9) Å] and the Ag-N-C angle [148.3 (7) and 148.8 (8)°] deviates significantly from linearity in both of these cases. The other Ag-N distances are between 2.207 (8) and 2.280 (8) Å with Ag-N-C angles between 165.4 (7) and 177.0 (7)°. N-Ag-N angles vary from 94.5 (3) to 120.3 (3)°. In the crystallographic overlay, the two AgI cations appear as approximate non-superimposable mirror images. The arrangement of the cations dominates the crystal packing with the anions occupying the spaces between the cations. There are no short Ag⋯anion contacts. The structure contains numerous short F⋯F contacts, which is unsurprising given the perfluorinated nature of the system, and there is an indication of C-F⋯π type inter-actions. 19F NMR spectra of the complex were consistent with the crystallographically determined structure with four perfluoro-benzo-nitrile ligands.