Identification and H(D)-bond energies of C–H(D)⋯Cl interactions in chloride–haloalkane clusters: a combined X-ray crystallographic, spectroscopic, and theoretical study

Abstract

The cationic (1,3,5-triazapentadiene)Pt^II complex [Pt{NHC(N(CH₂)₅)N(Ph)C(NH₂)NPh}₂]Cl₂ ([1]Cl₂) was crystallized from four haloalkane solvents giving [1][Cl₂(CDCl₃)₄], [1][Cl₂(CHBr₃)₄], [1][Cl₂(CH₂Cl₂)₂], and [1][Cl₂(C₂H₄Cl₂)₂] solvates that were studied by X-ray diffraction. In the crystal structures of [1][Cl₂(CDCl₃)₄] and [1][Cl₂(CHBr₃)₄], the Cl⁻ ion interacts with two haloform molecules via C–D⋯Cl⁻ and C–H⋯Cl⁻ contacts, thus forming the negatively charged isostructural clusters [Cl(CDCl₃)₂]⁻ and [Cl(CHBr₃)₂]⁻. In the structures of [1][Cl₂(CH₂Cl₂)₂] and [1][Cl₂(C₂H₄Cl₂)₂], cations [1]²⁺ are linked to a 3D-network by a system of H-bondings including one formed by each Cl⁻ ion with CH₂Cl₂ or C₂H₄Cl₂ molecules. The lengths and energies of these H-bonds in the chloride–haloalkane clusters were analyzed by DFT calculations (M06 functional) including AIM analysis. The crystal packing noticeably affected the geometry of the clusters, and energy of C–H⋯Cl⁻ hydrogen bonds ranged from 1 to 6 kcal mol⁻¹. An exponential correlation (R² > 0.98) between the calculated Cl⁻⋯H distances and the energies of the corresponding contacts was found and used to calculate hydrogen bond energies from the experimental Cl⁻⋯H distances. Predicted energy values (3.3–3.9 kcal mol⁻¹ for the [Cl(CHCl₃)₂]⁻ cluster) are in a reasonable agreement with the energy of the Cl₃C–H⋯Cl⁻ bond estimated using ATRFTIR spectroscopy (2.7 kcal mol⁻¹).