A Series of Discrete Dichloride Dihydrates: Characterisation and Symmetry Effects.

A series of three discrete dichloride dihydrates [Cl2 (H2 O)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(CH2 CF3 )2 )(NBu2 )2 ]+ (containing two 2,2,2-trifluoroethyl substituents) and C2v symmetry with the more fluorinated [C3 (N(CH2 CF3 )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 (H2 O)2 ]2- cluster with C2v symmetry to aid the infrared band assignments.