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)PtII 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).