Conformation-Associated C···-Pt Tetrel Bonding: The Case of Cyclometallated Platinum(II) Complex with 4-Cyanopyridyl Urea Ligand.

The nucleophilic addition of 3-(4-cyanopyridin-2-yl)-1,1-dimethylurea () to -[Pt(CNXyl)Cl] () gave a new cyclometallated compound . It was characterized by NMR spectroscopy (H, C, Pt) and high-resolution mass spectrometry, as well as crystallized to obtain two crystalline forms ( and ·2MeCN), whose structures were determined by X-ray diffraction. In the crystalline structure of , two conformers ( and ) were identified, while the structure ·2MeCN had only one conformer . The conformers differed by orientation of the ,-dimethylcarbamoyl moiety relative to the metallacycle plane. In both crystals and ·2MeCN, the molecules of the Pt(II) complex are associated into supramolecular dimers, either {} or {}, via stacking interactions between the planes of two metal centers, which are additionally supported by hydrogen bonding. The theoretical consideration, utilizing a number of computational approaches, demonstrates that the C···(Pt) interaction makes a significant contribution in the total stacking forces in the geometrically optimized dimer [] and reveals the (Pt)→π*(PyCN) charge transfer (CT). The presence of such CT process allowed for marking the C···Pt contact as a new example of a rare studied phenomenon, namely, tetrel bonding, in which the metal site acts as a Lewis base (an acceptor of noncovalent interaction).