X-ray crystal structures of alpha-KrF2, [KrF][MF6] (M = As, Sb, Bi), [Kr2F3][SbF6]center dot KrF2, [Kr2F3](2)[SbF6](2)center dot KrF2, and [Kr2F3][AsF6]center dot[KrF][AsF6]; Synthesis and characterization of [Kr2F3][PF6]center dot nKrF(2); and theoretical studies of KrF2, KrF+, Kr2F3+, and the [KrF][MF6] (M = P, As, Sb, Bi) ion pairs

The crystal structures of alpha -KrF2 and salts containing the KrF+ and Kr2 F3+ cations have been investigated for the first time using low-temperature single-crystal X-ray diffraction. The low-temperature a-phase of KrF2 crys tallizes in the tetragonal space group I4/mmm with a = 4.1790(6) Angstrom, c = 6.489(1) Angstrom, Z = 2, V = 113.32(3) Angstrom (3), R-1 = 0.0231, and wR(2) = 0.0534 at -125 degreesC. The [KrF][MF6] (M = As, Sb, Pi) salts are isomorphous and isostructural and crystallize in the monoclinic space grou p P2(1)/c with Z = 4. The unit cell parameters are as follows: beta-[KrF]-[ AsF6], a = 5.1753(2) Angstrom, b = 10.2019(7) Angstrom, c = 10.5763(8) Angs trom, beta = 95.298(2)degrees, V = 556.02(6) Angstrom (3), R-1= 0.0265, and wR(2) = 0.0652 at -120 degreesC; [KrF][SbF6], a 5.2922(6) Angstrom, b = 10 .444(1) Angstrom, c 10.796(1) Angstrom, beta = 94.693(4)degrees, V = 594.73 (1) Angstrom (3), R-1 = 0.0266, wR(2) = 0.0526 at -113 degreesC; [KrF][BiF6 ], a = 5.336(1) Angstrom, b = 10.513(2) Angstrom, c = 11.046(2) Angstrom, b eta = 94.79(3)degrees, V = 617.6(2) Angstrom (3), R-1 = 0.0344, and wR(2) = 0.0912 at -130 degreesC. The Kr2F3+ cation was investigated in [Kr2F3][SbF 6]. KrF2, [Kr2F3](2)[SbF6](2). KrF2, and [Kr2F3][AsF6]. [KrF][AsF6]. [Kr2F3 ](2)-[SbF6](2). KrF2 crystallizes in the monoclinic P2(1)/c space group wit h Z = 4 and a = 8.042(2) Angstrom, b = 30.815(6) Angstrom, c = 8.137(2) Ang strom, beta = 111.945(2) Angstrom, V = 1870.1(7) Angstrom (3), R-1 = 0.0376 , and wR(2) = 0.0742 at -125 degreesC. [Kr2F3]-[SbF6]. KrF2 crystallizes in the triclinic P (1) over bar space group with Z = 2 and a = 8.032(3) Angst rom, b = 8.559(4) Angstrom, c = 8.948(4) Angstrom, alpha = 69.659(9)degrees , beta = 63.75(1)degrees, gamma = 82.60(1)degrees, V = 517.1(4) Angstrom (3 ), R-1 = 0.0402, and wR(2) = 0.1039 at -113 degreesC. [Kr2F3][AsF6]. [KrF][ AsF6] crystallizes in the monoclinic space group P2(1)/c with Z = 4 and a = 6.247(1) Angstrom, b = 24.705(4) Angstrom, c = 8.8616(6) Angstrom, beta = 90.304(6)degrees, V = 1367.6(3) Angstrom (3), R-1 = 0.0471 and wR(2) = 0.09 58 at -120 degreesC. The terminal Kr-F bond lengths of KrF+ and Kr2F3+ are very similar, exhibiting no crystallographically significant variation in t he structures investigated (range, 1.765(3)-1.774(6) Angstrom and 1.780(7)- 1.805(3) Angstrom in the KrF+ salts and from 2.027(5) to 2.065(4) Angstrom in the Kr2F3+ salts. The Kr-F bond lengths of KrF2 in [Kr2F3 ][SbF6]. KrF2 and [Kr2F3](2)[SbF6](2). KrF2 range from 1.868(4) to 1.888(4) Angstrom and are similar to those observed in alpha -KrF2 (1.894(5) Angstrom). The synth esis and Raman spectrum of the new salt, [Kr2F3][PF6]. nKrF(2), are also re ported. Electron structure calculations at the Hartree-Fock and local density-funct ional theory levels were used to calculate the gas-phase geometries, charge s, Mayer bond orders, and Mayer valencies of KrF+, KrF2, Kr2F3+, and the io n pairs, [KrF][MF6] (M = P, As, Sb, Bi), and to assign their experimental v ibrational frequencies.