Metal-Involving Chalcogen Bond. The Case of Platinum(II) Interaction with Se/Te-Based σ-Hole Donors

Abstract

Platinum(II) complexes exhibiting an expressed <i>d</i>_<i>z</i>²-nucleophilicity of the positively charged metal centers, namely, [Pt(ppy)(acac)] (<b>1</b>; acacH is acetylacetone; ppyH is 2-Ph-pyridine) and [Pt(ppy)(tmhd)] (<b>2</b>; tmhdH is 2,2,6,6-tetramethylheptanedione-3,5), were cocrystallized with the chalcogen bond donors (4-NC₅F₄)₂Ch (Ch = Se, Te) to form two isostructural cocrystals <b>1</b>·¹/₂(4-NC₅F₄)₂Ch, and <b>2</b>·²/₃(4-NC₅F₄)₂Se and <b>2</b>·(4-NC₅F₄)₂Te. The X-ray data for these cocrystals and appropriate theoretical DFT calculations (PBE0-D3BJ) allowed the recognition of the metal-involving chalcogen bond, namely, Ch···<i>d</i>_<i>z</i>²-Pt^II (its energy spans from -7 to -12 kcal/mol). In <b>1</b>·¹/₂(4-NC₅F₄)₂Ch, Ch···<i>d</i>_<i>z</i>²-Pt^II bonding is accompanied by the C···<i>d</i>_<i>z</i>²-Pt^II interaction, representing a three-center bifurcate, whereas in <b>2</b>·(4-NC₅F₄)₂Te the chalcogen bond Te···<i>d</i>_<i>z</i>²-Pt^II is purely two-centered and is stronger than that in <b>1</b>·¹/₂(4-NC₅F₄)₂Ch because of more efficient orbital overlap. The association of <b>2</b> with (4-NC₅F₄)₂Te and the structure of the formed adduct in CDCl₃ solutions was studied by using ¹H, ¹³C, ¹⁹F, ¹⁹⁵Pt, ¹²⁵Te NMR, ¹⁹F-¹H HOESY, and diffusion NMR methods. The ¹⁹⁵Pt and ¹²⁵Te NMR titration and the isothermal titration calorimetry results revealed a 1:1 association of <b>2</b> with (4-NC₅F₄)₂Te.