Linear and Bent Noncovalent M···S═C═N–M′ Interactions: The Case of Palladium(II) and Platinum(II) Thiocyanate Species

Abstract

Analysis of X-ray crystal structures of newly prepared thiocyanate PdII and PtII complexes revealed the bifurcated (M–N)···S contacts in which angles ∠M···S═C are close to 180°. All M···S═C═N–M′ noncovalent interactions─identified in this study and also those found on the Cambridge Structural Database search─were systematized as linear (approximately 180°) and bent (∠M···S═C 80–120°). Results of appropriate theoretical study indicate that, although the linear configuration of the PdII and PtII structures is primarily determined by crystal packing effects, the attractive M···S forces are far from negligible and the linear structures correspond to the energy minimum. Furthermore, the linear arrangement is mostly determined by orbital interactions, while the bent configuration by electrostatic forces. Molecular electrostatic potential (MEP) surfaces along with the quantum theory of “atoms-in-molecules” (QTAIM) and the noncovalent interaction plot index (NCIPlot) computational tools were used to characterize the bifurcated (M–N)···S interactions. The nature of the noncovalent M···S═C═N–M′ forces in the PdII and PtII structures was established by NBO analysis: in both cases, the predominant donor–acceptor orbital interactions include the charge transfer from lone pair orbitals located at the M atom to the σ*-orbital of the S–C bond of a thiocyanate ligand from a neighboring complex.