A Series of Discrete Dichloride Dihydrates: Characterisation and Symmetry Effects

Abstract

A series of three discrete dichloride dihydrates [Cl2(H2O)2]2− have been isolated with different triaminocyclopropenium (TAC) cations and with different crystallographic symmetries. The cluster exhibits D2h symmetry with the tris(dimethylamino)cyclopropenium cation [C3(NMe2)3]+, C2h symmetry with the fluorinated cation [C3(N(CH2CF3)2)(NBu2)2]+ (containing two 2,2,2‐trifluoroethyl substituents) and C2v symmetry with the more fluorinated [C3(N(CH2CF3)2)2(NBu2)]+ cation. The effect of symmetry on the infrared spectra of the dichloride ion‐pair clusters, as well as deuterated analogues, has been investigated. The D2h‐ and C2h‐symmetric clusters each exhibit two stretching bands in the infrared at 3427 and 3368 cm−1 for D2h symmetry and 3444 and 3392 cm−1 for C2h symmetry, whereas the C2v‐symmetric cluster exhibits three bands at 3475, 3426 and 3373 cm−1. Computational studies were carried out on a [Cl2(H2O)2]2− cluster with C2v symmetry to aid the infrared band assignments.

Structures and Spectra of Halide Hydrate Clusters in the Solid State: A Link between the Gas Phase and Solution State

“… Mid‐IR spectra in the O−H stretching region for encapsulated chloride hydrates in the solid state: (a) [Cl(H 2 O)] − ; (b) [Cl 2 (H 2 O)] 2− ; (c) D 2h [Cl 2 (H 2 O) 2 ] 2− ; (d) C 2h [Cl 2 (H 2 O) 2 ] 2− ; (e) C 2v [Cl 2 (H 2 O) 2 ] 2− ; (f) [Cl 2 (H 2 O) 4 ] 2− ; (g) [Cl 2 (H 2 O) 6 ] 2− ; (h) [Cl 4 (H 2 O) 4 ] 4− ; (i) {[Cl(H 2 O)] − } ∞ [6,9,11–14] …”

Discrete Oligomers and Polymers of Chloride Monohydrate Can Form in Encapsulated Environments: Structures and Infrared Spectra of [Cl4(H2O)4]4− and {[Cl(H2O)]−}∞

“…We have recently been investigating the synthesis and properties of partially‐fluorinated TAC salts. We have previously reported that treatment of tetrachlorocyclopropene with NH(CH 2 CF 3 ) 2 and NBu 3 leads primarily to a mixture of [C 3 (N(CH 2 CF 3 ) 2 ) 2 (NBu 2 )]Cl and [C 3 (N(CH 2 CF 3 ) 2 )(NBu 2 )Cl]Cl, and that the latter can be further treated with the secondary amine NHBu 2 to give [C 3 (N(CH 2 CF 3 ) 2 )(NBu 2 ) 2 ]Cl [9] . By using the less bulky tertiary amine NEt 3 instead of NBu 3 , a small amount of the diaminochloro‐TAC cation [C 3 (N(CH 2 CF 3 ) 2 )(NEt 2 )Cl] + is produced (Scheme 1).…”

“… The structures of known discrete chloride hydrates (a) [Cl(H 2 O)] − ; (b) [Cl 2 (H 2 O) 2 ] 2− ; (c) [Cl 2 (H 2 O)] 2− ; (d) [Cl 2 (H 2 O) 4 ] 2− ; (e) [Cl 2 (H 2 O) 6 ] 2− [1,9,17–19] …”

“…More commonly, chloride monohydrate is found in the solid state as its dimer dichloride dihydrate, [Cl 2 (H 2 O) 2 ] 2− (Figure 1b), which has been calculated to be metastable in the gas phase [7,8] . We have recently reported three discrete examples of this dimer, each with different crystallographic symmetry ( D 2h , C 2h and C 2v ) [9] . In each case, we used triaminocyclopropenium (TAC) cations as the counterion as they are known to have weak cation‐anion interactions [10,11] .…”

“…However, vibrational modes associated only with chloride hydrates can be hard to pinpoint due to the presence of overlapping bands from other species present (e. g. OH and/or NH stretching modes). We have recently reported infrared and far‐infrared band centres for several discrete chloride hydrate species encapsulated within cyclopropenium salts, using a selective deuteration strategy to clearly and uniquely identify the relevant vibrational transitions [1,9,17–19] …”