Dimers and Chains of Hydrogen bonded [HS₂O₇]^– Anions in the Crystal Structures of M[HS₂O₇] (M = K, [NH₄], [NO], Rb, Cs)

Abstract

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, P2 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) ϫ 10 6 pm 3 ), [NH 4 ][HS 2 O 7 ] (monoclinic, P2 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) ϫ 10 6 pm 3 ), Rb[HS 2 O 7 ] (monoclinic, P2 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) ϫ 10 6 pm 3 ), and Cs[HS 2 O 7 ] (triclinic, P1 (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)°, * Prof. Dr. M. S. Wickleder

Stabilizing Superacid Anions: The New [H(S4O13)2]3− Anion in the Crystal Structure of Li3[H(S4O13)2]

“…Even if these superacids are not known, we recently reported on the first conjugated base of trisulfuric acid—the highly acidic [HS 3 O 10 ] − anion—stabilized in salts with various monovalent counter cations . Similar to the previously described hydrogendisulfates, exhibiting the [HS 2 O 7 ] − anion, a main feature of these structures is the linkage of the [HS 3 O 10 ] − anions via hydrogen bonds to chains and dimers. According to the observed donor–acceptor distances of about 245 pm these hydrogen bonds are very strong and essentially symmetric .…”

“…The donor–acceptor distance of 242.9(5) pm and the D ‐H‐A angle of 180° indicate the strength of the hydrogen bond according to the classification of Jeffrey . The D –A distance is only by about 8 % longer than in the structure of the hydrogen bifluoride anion [HF 2 ] − which is the prime example for very strong hydrogen bonding and even shorter than in the symmetrical intramolecular hydrogen bond in the structure of potassium hydrogen maleate (243.7(4) pm) (another archetype of symmetric hydrogen bonds) and the above mentioned hydrogentrisulfates (Na[HS 3 O 10 ]: 254.31(6) pm, K[HS 3 O 10 ]: 247.7(1) pm, Rb[HS 3 O 10 ]: 245.7(1) pm) …”

Towards Polysulfuric Acids: The Hydrogentrisulfate Anion [HS3O10]− in A[HS3O10] (A=Na, K, Rb)

“…Such long-chained acids are still elusive but theoreticali nvestigations reveal that they are strong superacids exhibiting increasing acidity with growing chain length, that is, large numbers for n. [2] Even if these superacids are not known, we recently reported on the first conjugated base of trisulfuric acid-theh ighly acidic [HS 3 O 10 ] À anion-stabilized in salts with various monovalent counter cations. [3] Similar to the previously described hydrogendisulfates, exhibitingt he [HS 2 O 7 ] À anion, [4] am ain feature of these structures is the linkageoft he [HS 3 O 10 ] À anions via hydrogen bonds to chains and dimers. According to the observed donor-acceptor distances of about 245 pm these hydrogen bonds are very stronga nd essentially symmetric.…”

“…[3] Similar to the previously described hydrogendisulfates, exhibitingt he [HS 2 O 7 ] À anion, [4] am ain feature of these structures is the linkageoft he [HS 3 O 10 ] À anions via hydrogen bonds to chains and dimers. [5] In the present work we pass one step furthert ot he hydrogen containing saltso f tetrasulfuric acid, H 2 S 4 3 .Inexperiments performed via this synthetic route, ex-cessive SO 3 usually crystallizesi nt he asbestos-type modification, which is ah int for ar emaining quantity of water as the asbestos-like modifications a-a nd b-SO 3 are in fact very long chained polysulfuric acids. [5] In the present work we pass one step furthert ot he hydrogen containing saltso f tetrasulfuric acid, H 2 S 4 3 .Inexperiments performed via this synthetic route, ex-cessive SO 3 usually crystallizesi nt he asbestos-type modification, which is ah int for ar emaining quantity of water as the asbestos-like modifications a-a nd b-SO 3 are in fact very long chained polysulfuric acids.…”

“…[7] Ah ydrogen atom located between the two terminal oxygen atoms O13 on the special Wyckoff position2 b with site symmetry " 1l inks two tetrasulfate anions via av ery short symmetrical hydrogenb ond to the up to now unknown [11] and Li[H(HS 2 O 7 ) 2 ]. [4] The cations are located on two distinguishable positions, Li1 on the special Wyckoff position 2d with site symmetry " 1, Li2 on ag eneral position4 e.B oth Li cations show as lightly dis-torted octahedralc oordination by six oxygen atoms in the distance range from 199.6(2) pm to 226.6(2) pm, the distortion of the coordination polyhedron of Li2 is al ittle bit stronger due to the lower site symmetry.T he bridging oxygen atomsa sw ell as the protonated oxygen atom O13 do not take part in the cation coordination. In all of the other above-mentioned structures the hydrogen atom is either not found at all or the differenceF ourierm aps show two symmetrically equivalent positions close to the center of symmetry or ab road blurred electron density.T he donor-acceptor distance of 242.9(5) pm and the D-H-A angle of 1808 indicatet he strength of the hydrogen bond according to the classification of Jeffrey.…”