Intermolecular Metal-Involving Pnictogen Bonding: The Case of σ-(SbIII)-Hole<middle dot><middle dot><middle dot>d z 2 [PtII] Interaction

Cocrystallizations of trans-[PtX'(2)(NCNR2)(2)] (R-2 = Me-2, X' = Cl 1a, Br 1b, I 1c; R-2 = (CH2)(5), X' = I 2c) with SbX3 (X = Cl, Br, I) gave 1:2 cocrystals 1a<middle dot>2SbCl(3), 1b<middle dot>2SbBr(3), 1c<middle dot>2SbCl(3), 1c<middle dot>2SbBr(3), 1c<middle dot>2SbI(3), and 2c<middle dot>2SbI(3). In all six X-ray structures, the association of the molecular coformers is achieved mainly by Sb-III<middle dot><middle dot><middle dot>d(z)(2)[Pt-II] metal-involving intermolecular pnictogen bonding. Density functional theory (DFT) calculations (based on experimentally determined geometries) using both gas-phase and solid-state approximations revealed that a sigma-(Sb)-hole interacts with an area of negative potential associated with the d(z)(2)-orbital of the positively charged platinum(II) sites, thus forming a pnictogen bond whose energy falls in the range between -7.3 and -16.9 kcal/mol.