Dimers and Chains of Hydrogen bonded [HS 2 O 7 ] – Anions in the Crystal Structures of M [HS 2 O 7 ] ( M = K, [NH 4 ], [NO], Rb, Cs)

The reactions of KCl, [NH 4 ] 2 [SO 4 ], Rb 2 [CO 3 ], and Cs 2 [CO 3 ] with fuming sulfuric acid (65 % SO 3 ) yielded colorless and moisture sensitive crystals of K[HS 2 O 7 ] (monoclinic, P 2 1 / c (no. 14), Z = 4, a = 716.67(3) pm, b = 1043.57(4) pm, c = 828.78(3) pm, β = 107.884(1)°, V = 589.89(4) × 10 6 pm 3 ), [NH 4 ][HS 2 O 7 ] (monoclinic, P 2 1 / c (no. 14), Z = 4, a = 729.29(1) pm, b = 1079.73(1) pm, c = 843.26(1) pm, β = 106.397(1)°, V = 637.01(1) × 10 6 pm 3 ), Rb[HS 2 O 7 ] (monoclinic, P 2 1 / c (no. 14), Z = 4, a = 724.49(2) pm, b = 1073.19(3) pm, c = 852.01(3) pm, β = 106.534(1)°, V = 635.06(3) × 10 6 pm 3 ), and Cs[HS 2 O 7 ] (triclinic, P $\bar{1}$ (no. 2), Z = 2, a = 537.61(3) pm, b = 784.71(4) pm, c = 867.93(4) pm, α = 94.214(2)°, β = 103.138(2)°, γ = 105.814(2)°, V = 339.47(3) × 10 6 pm 3 ). Colorless crystals of [NO][HS 2 O 7 ] (monoclinic, P 2 1 / c (no. 14), Z = 4, a = 739.90(4) pm, b = 1048.00(5) pm, c = 830.97(4) pm, β = 106.985(2)°, V = 106.985(2) × 10 6 pm 3 ) were obtained as a side product from the reaction of [NH 4 ] 2 [Rh(NO 2 ) 4 ] with oleum (65 % SO 3 ) in the ionic liquid [BMIm][OTf]. The crystal structures of K[HS 2 O 7 ], [NH 4 ][HS 2 O 7 ], [NO][HS 2 O 7 ], and Rb[HS 2 O 7 ] show the [HS 2 O 7 ] – ions linked into dimers by strong hydrogen bonds. Contrastingly, in the crystal structure of Cs[HS 2 O 7 ] the [HS 2 O 7 ] – ions are connected to infinite chains. Raman spectra were recorded for M [HS 2 O 7 ] ( M = K, Rb, Cs).