Exceptional Structural Compliance of the BF Superweak Anion.

The single-crystal X-ray structures, thermogravimetric analyses, and/or FTIR spectra of a series of salts of the BF anion and homoleptic Ag(L) cations are reported (L = CHCl, n = 2; L = PhCH, n = 3; L = CHCN; n = 2-4; L = CO, n = 1, 2). The superweak-anion nature of BF (Y) was demonstrated by the rapid reaction of microcrystalline Ag(Y) with 1 atm of CO to form a nonclassical silver(I) carbonyl compound with an FTIR ν(CO) band at 2198 cm (and with the proposed formula [Ag(CO)][Y]). In contrast, microcrystalline Ag(BCl) did not exhibit ν(CO) bands and therefore did not form Ag(CO) species, even after 32 h under 24 atm of CO. When Ag(Y) was treated with carbon monoxide pressures higher than 1 atm, a new ν(CO) band at 2190 cm appeared, which is characteristic of a Ag(CO) dicarbonyl cation. Both Ag(CHCN)(Y) and Ag(CHCN)(Y) rapidly lost coordinated CHCN at 25 °C to form Ag(CHCN)(Y), which formed solvent-free Ag(Y) only after heating above 100 °C. Similarly, Ag(PhCH)(Y) rapidly lost coordinated PhCH at 25 °C to form Ag(PhCH)(Y), which formed Ag(Y) after heating above 150 °C, and Ag(CHCl)(Y) rapidly lost three of the four coordinated CHCl ligands between 25 and 100 °C and formed Ag(Y) when it was heated above 200 °C. Solvent-free Ag(Y) was stable until it was heated above 380 °C. The rapid evaporative loss of coordinated ligands at 25 °C from nonporous crystalline solids requires equally rapid structural reorganization of the lattice and is one of three manifestations of the structural compliance of the Y anion reported in this work. The second, more quantitative, manifestation is that Ag bond-valence sums for Ag(CHCN)(Y) are virtually constant, 1.20 ± 0.03, for n = 8, 5, 4, because the Y anion precisely compensated for the lost CHCN ligands by readily forming the necessary number of weak Ag-F(B) bonds. The third, and most exceptional, manifestation is that the idealized structural reorganization accompanying the conceptual transformations Ag(CHCN)(Y) → Ag(CHCN)(Y) → Ag(CHCN)(Y) involve close-packed layers of Y anions that sandwich the Ag(CHCN) complexes splitting into staggered flat ribbons of interconnected (Y) triangles that surround the Ag(CHCN) complexes on four sides, conceptually re-forming close-packed layers of anions that sandwich the Ag(CHCN) complexes. The interconnected (Y) triangle lattice of anions in Ag(CHCN)(Y) may be the first example of this structure type.