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

The cationic (1,3,5-triazapentadiene)Pt II complex [Pt{NH&z.dbd;C(N(CH 2 ) 5 )N(Ph)C(NH 2 )&z.dbd;NPh} 2 ]Cl 2 ([ 1 ]Cl 2 ) was crystallized from four haloalkane solvents giving [ 1 ][Cl 2 (CDCl 3 ) 4 ], [ 1 ][Cl 2 (CHBr 3 ) 4 ], [ 1 ][Cl 2 (CH 2 Cl 2 ) 2 ], and [ 1 ][Cl 2 (C 2 H 4 Cl 2 ) 2 ] solvates that were studied by X-ray diffraction. In the crystal structures of [ 1 ][Cl 2 (CDCl 3 ) 4 ] and [ 1 ][Cl 2 (CHBr 3 ) 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(CDCl 3 ) 2 ] − and [Cl(CHBr 3 ) 2 ] − . In the structures of [ 1 ][Cl 2 (CH 2 Cl 2 ) 2 ] and [ 1 ][Cl 2 (C 2 H 4 Cl 2 ) 2 ], cations [ 1 ] 2+ are linked to a 3D-network by a system of H-bondings including one formed by each Cl − ion with CH 2 Cl 2 or C 2 H 4 Cl 2 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 ( R 2 > 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(CHCl 3 ) 2 ] − cluster) are in a reasonable agreement with the energy of the Cl 3 C-H Cl − bond estimated using ATRFTIR spectroscopy (2.7 kcal mol −1 ). An exponential correlation was found between interatomic H Cl − distances and energies of the corresponding C-H Cl − contacts in the solid state.