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

Abstract

This Review describes and assesses known solid‐state examples of halide hydrates that are discrete in nature. Most of these are chloride hydrates, and most discrete clusters are dihalides, with very few mono‐ or multi‐halide species found in the solid state. Polymeric chloride hydrates, on the other hand, are mostly 2D layered structures. We also observe that there is a gap in the chloride:water ratio between 8–20 waters per chloride. Isolated clusters can be found with 1–3 waters per chloride, 2D layers with 2–8 waters, and 3D semiclathrates with 20–38 waters. However, 1D chains comprise only 1–2 waters per chloride. [Cl(H2O)]− is the only species found in both the solid state and gas phase and is also the only halide hydrate with a free OH group. Infrared spectra in the ν(OH) region are distinctive and useful for identification. Agreement between computed (gas phase) and experimentally‐observed solid state structures and their vibrational spectra gives us confidence that discrete halide hydrate species observed in the solid state provide a useful link between gas phase species and structural motifs of halide hydrates in solution, especially microsolvated ion‐pairs.

Halocyclopropenium‐Halide Halogen‐Bonded Ion Pairs and Their Hydrogen‐Bonded Halide Solvates

“…Another notable feature of the halogen-bonded chloride ions is their pyramidal geometries; the ClÀ ClÀ H angles being either very acute (77.222( 16)°a nd 76.652(15)°) or nearer 100°(99.598(17)°and 107.91(2)°) while the HÀ ClÀ H angles are both acute (81.488(16)°and 81.444(18)°). This is in fact a common feature of chloride geometries involving weak bonds, [52] as we will also see in the other salts described here.…”

Highly‐fluorinated Triaminocyclopropenium Ionic Liquids

“…The cluster in [ 1 b ]Cl.H 2 O has longer Cl−O distances (3.262(5) and 3.31(5) Å versus 3.2051(15) and 3.2975(15) Å) and, consequently, the infrared stretching bands (Figure 7S) are at higher energy and the bending bands are at lower energy (Table 18S). Curnow and Crittenden have recently reviewed the structures and infrared spectra of halide hydrates in the solid state [55] …”

“…Curnow and Crittenden have recently reviewed the structures and infrared spectra of halide hydrates in the solid state. [55] Crystals of [C 3 (N(CH 2 CF 3 ) 2 ) 2 (NEt 2 )]Cl.2.17H 2 O ([1 a]Cl.2.17H 2 O) were obtained by slow evaporation of a CH 2 Cl 2 /EtOH solution at room temperature. It crystallizes in the triclinic space group P-1 (Table 9S).…”

Molecular Insights into Water–Chloride and Water–Water Interactions in the Supramolecular Architecture of Aconine Hydrochloride Dihydrate

“…5 The interaction between water and chloride is of great significance in biological environments, as well as in seawater and various geological/atmospheric processes. 13 However, in the crystal structure, the water−chloride interaction plays a crucial role in the nucleation and growth of molecular crystals, effectively modifying the physicochemical properties of APIs. 14 Additionally, calculated interaction energies for H 2 O•••Cl − clusters confirm that the water−chloride interaction is primarily the electrostatic attraction.…”

“… 2 The distinctive characteristics of water molecule, including its relatively small size, high polarity, and ability to form hydrogen bonding network, make it indispensable building materials in the field of crystal engineering. 12 Hydrogen bonding interactions involving water molecule can be classified into three groups: water–chloride, 13 water–water, 14 and water–host. 15 Among these interactions, the water–chloride and water–water interactions are particularly significant in the crystal engineering since they greatly contribute to the overall supramolecular assembly or aggregate in hydrated HCl salts.…”