Exceptional Structural Compliance of the B12F122- Superweak Anion

The single-crystal X-ray structures, thermogravimetric analyses, and/or FTIR spectra of a series of salts of the B12F122- anion and homoleptic Ag(L)(n)(+) cations are reported (L = CH2Cl2, n = 2; L = PhCH3, n = 3; L = CH3CN; n = 2-4; L = CO, n = 1, 2). The superweak-anion nature of Bi2F122- (Y2-) was demonstrated by the rapid reaction of microcrystalline Ag-2(Y) with 1 atm of CO to form a nonclassical silver(I) carbonyl compound with an FTIR v(CO) band at 2198 cm(-1) (and with the proposed formula [Ag(CO)(n)](2)[Y]). In contrast, microcrystalline Ag-2(B12Cl12) did not exhibit v(CO) bands and therefore did not form Ag(CO)(+) species, even after 32 h under 24 atm of CO. When Ag-2(Y) was treated with carbon monoxide pressures higher than 1 atm, a new v(CO) band at 2190 cm(-1) appeared, which is characteristic of a Ag(CO)(2)(+) dicarbonyl cation. Both Ag-2(CH3CN)(8)(Y) and Ag-2(CH3CN)(5)(Y) rapidly lost coordinated CH3CN at 25 degrees C to form Ag-2(CH3CN)(4)(Y), which formed solvent-free Ag-2(Y) only after heating above 100 degrees C. Similarly, Ag-2(PhCH3)(6)(Y) rapidly lost coordinated PhCH3 at 25 degrees C to form Ag-2(PhCH3)(2)(Y), which formed Ag-2(Y) after heating above 150 degrees C, and Ag-2(CH2Cl2)(4)(Y), rapidly lost three of the four coordinated CH2Cl2 ligands between 25 and 100 degrees C and formed Ag-2(Y) when it was heated above 200 degrees C. Solvent-free Ag-2(Y) was stable until it was heated above 380 degrees C. The rapid evaporative loss of coordinated ligands at 25 degrees 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 Y2- anion reported in this, work. The second, more quantitative, manifestation is that Ag+ bond-valence sums for Ag-2(CH3CN)(n)(Y) are virtually constant, 1.20 +/- 0.03, for n = 8, 5, 4, because the Y2- anion precisely compensated for the lost CH3CN 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-2(CH3CN)(8)(Y) -> Ag-2(CH3CN)(5)(Y) -> Ag-2(CH3CN)(4)(Y) involve close-packed layers of Y2- anions that sandwich the Ag(CH3CN)(4)(+) complexes splitting into staggered flat ribbons of interconnected (Y2-)(3) triangles that surround the Ag-2(CH3CN)(5)(2+) complexes on four sides, conceptually re-forming close-packed layers of anions that sandwich the Ag(CH3CN)(2)(+) complexes. The interconnected (Y2-)(3) triangle lattice of anions in Ag-2(CH3CN)(5)(Y) may be the first example of this structure type.