A Borane Platinum Complex Undergoing Reversible Hydride Migration in Solution

Reaction of [Pt­(κ²-<i>C</i>,<i>N</i>-ppy)­(dmso)­Cl], <b>1</b> (Hppy = 2-phenylpyridine), with Na­[H₂B­(mb)₂] (Hmb = 2-mercapto-benzimidazole) smoothly afforded the complex {[(κ³-<i>S</i>,<i>B</i>,<i>S</i>-HB­(mb)₂]­Pt­(κ²-<i>C</i>,<i>N</i>-ppy)­H}, <b>2</b>, featuring a strong reverse-dative Pt → B σ interaction in the solid state. When dissolved in thf (or acetone) solution, <b>2</b> undergoes a reversible Pt–H bond activation, establishing an equilibrium between the hexacoordinated <b>2</b> and the tetracoordinate complex {[(κ²-<i>S</i>,<i>S</i>-H₂B­(mb)₂]­Pt­(κ²-<i>C</i>,<i>N</i>-ppy)}, <b>3</b>, as ascertained by multinuclear NMR. Hydrolysis of the B–N bond in <b>2</b>/<b>3</b> resulted ultimately in the formation of a dimeric half-lantern platinum­(II,II) complex [{Pt­(κ²-<i>C</i>,<i>N</i>-ppy)­(μ₂-κ²-<i>N</i>,<i>S</i>-mb)}₂], <b>4</b>. The SC-XRD structures of <b>2</b> and <b>4</b> are reported

Photophysical Responses in Pt₂Pb Clusters Driven by Solvent Interactions and Structural Changes in the Pb^II Environment

Two types of Pt₂Pb luminescent clusters were successfully prepared by the reaction of [Pt­(C₆F₅)­(bzq)­(OCMe₂)] (<b>1</b>) and [Pt­(C₆F₅)­(ppy)­(dmso)] (<b>2</b>) with [Pb­(SpyR-5)₂] (R = H, CF₃). Thus, whereas <b>5</b> (ppy, Spy) is generated through coordination of the pyridine-N atoms to the Pt centers, the formation of <b>3</b>, <b>4</b> (bzq), and <b>6</b> (ppy, SpyCF₃) is accompanied by a formal thiolate transfer from Pb^II to Pt^II, keeping the two N atoms in the primary environment of the lead. In <b>5</b>, the <i>neutral</i> Pb center adopts a rather stable and symmetrical “Pt₂S₂” coordination sphere supplemented by two Pb··F_<i>o</i> contacts, whereas for the remaining species several pseudopolymorphs were found depending on the solvent (<b>3</b>, <b>4</b>) and crystallization conditions (<b>6</b>). This structural diversity relies on changes in the coordination mode of the SpyR ligands (μ-κ<i>S</i>,<i>N</i>/μ-κ³<i>S</i>,<i>N</i>,<i>S</i>), intermetallic Pt–Pb bonds, and secondary <i>intra-</i> and <i>intermolecular</i> contacts induced by Pb–solvent binding. Notably, the changes, which entail a slight tuning of the stereochemical activity of the lone pair, have also a remarkable impact on the emissive state (³L′CCT/³L′LCT, SpyR → Pb,Pt/(C^∧N) in nature). Clusters <b>3</b> and <b>4</b> display a distinct and fast reversible blue shift vapoluminescent response (<b>4</b> shows also color changes) to donor solvents, correlated with changes in the environment of the Pb^II ion (asymmetric <i>hemidirected</i> to more symmetric <i>holodirected</i>) upon solvent binding and, additionally, in <b>4</b> with modifications in the crystal packing, as confirmed by XRD and supported by TD-DFT calculations. <b>5</b> and <b>6</b> do not show a vapoluminescent response. However, for <b>6</b>, three different and interconvertible forms, a symmetrical form (yellow <b>6-y</b>) and two asymmetrical forms with a rather short Pt–Pb bond (pale orange <b>6·acetone</b> and orange <b>6-o</b>), exhibiting different emissions were found. Notably, slow crystallization and low concentration favor the formation of the <i>thermodynamically</i> more stable yellow form, whereas fast crystallization gives rise to orange solids with a remarkable red shift of the emission. Interestingly, <b>6</b> also exhibits reversible <i>mechanochromic</i> color and luminescence changes

Photophysical Responses in Pt₂Pb Clusters Driven by Solvent Interactions and Structural Changes in the Pb^II Environment

Two types of Pt₂Pb luminescent clusters were successfully prepared by the reaction of [Pt­(C₆F₅)­(bzq)­(OCMe₂)] (<b>1</b>) and [Pt­(C₆F₅)­(ppy)­(dmso)] (<b>2</b>) with [Pb­(SpyR-5)₂] (R = H, CF₃). Thus, whereas <b>5</b> (ppy, Spy) is generated through coordination of the pyridine-N atoms to the Pt centers, the formation of <b>3</b>, <b>4</b> (bzq), and <b>6</b> (ppy, SpyCF₃) is accompanied by a formal thiolate transfer from Pb^II to Pt^II, keeping the two N atoms in the primary environment of the lead. In <b>5</b>, the <i>neutral</i> Pb center adopts a rather stable and symmetrical “Pt₂S₂” coordination sphere supplemented by two Pb··F_<i>o</i> contacts, whereas for the remaining species several pseudopolymorphs were found depending on the solvent (<b>3</b>, <b>4</b>) and crystallization conditions (<b>6</b>). This structural diversity relies on changes in the coordination mode of the SpyR ligands (μ-κ<i>S</i>,<i>N</i>/μ-κ³<i>S</i>,<i>N</i>,<i>S</i>), intermetallic Pt–Pb bonds, and secondary <i>intra-</i> and <i>intermolecular</i> contacts induced by Pb–solvent binding. Notably, the changes, which entail a slight tuning of the stereochemical activity of the lone pair, have also a remarkable impact on the emissive state (³L′CCT/³L′LCT, SpyR → Pb,Pt/(C^∧N) in nature). Clusters <b>3</b> and <b>4</b> display a distinct and fast reversible blue shift vapoluminescent response (<b>4</b> shows also color changes) to donor solvents, correlated with changes in the environment of the Pb^II ion (asymmetric <i>hemidirected</i> to more symmetric <i>holodirected</i>) upon solvent binding and, additionally, in <b>4</b> with modifications in the crystal packing, as confirmed by XRD and supported by TD-DFT calculations. <b>5</b> and <b>6</b> do not show a vapoluminescent response. However, for <b>6</b>, three different and interconvertible forms, a symmetrical form (yellow <b>6-y</b>) and two asymmetrical forms with a rather short Pt–Pb bond (pale orange <b>6·acetone</b> and orange <b>6-o</b>), exhibiting different emissions were found. Notably, slow crystallization and low concentration favor the formation of the <i>thermodynamically</i> more stable yellow form, whereas fast crystallization gives rise to orange solids with a remarkable red shift of the emission. Interestingly, <b>6</b> also exhibits reversible <i>mechanochromic</i> color and luminescence changes

Cyclometalated Platinum(II) Complexes Bearing Bidentate <i>O</i>,<i>O</i>′‑Di(alkyl)dithiophosphate Ligands: Photoluminescence and Cytotoxic Properties

Mononuclear complexes [Pt­(ppy)­(S^∧S)] (<b>1a</b>, S^∧S = <i>O</i>,<i>O</i>′-di­(cyclohexyl)­dithiophos­phate (ctp); <b>2a</b>, S^∧S = <i>O</i>,<i>O</i>′-di­(butyl)­dithiophos­phate (btp)) and [Pt­(bzq)­(S^∧S)] (<b>1b</b>, S^∧S = ctp; <b>2b</b>, S^∧S = btp) have been prepared by the reaction of precursor complexes [Pt­(C^∧N)­Cl­(dmso)], C^∧N = deprotonated form of 2-phenylpyrdine (ppy) and 7,8-benzoquinoline (bzq), and potassium salt of S^∧S ligands. All complexes were characterized by NMR spectroscopy, and the structure of <b>2b</b> was further identified by single crystal X-ray determination. Although the complexes are not luminescent in solution at ambient temperature, they become strong emissive materials (bright green) in solid state (at room temperature) with high quantum yields and long lifetimes in the microsecond domain. In frozen glass state or at low temperature (solid state), these complexes become better emissive in relation to room temperature. UV–vis spectra, supported by TD-DFT calculations, indicate that ¹ILCT (intraligand charge transfer) predominates over the other transitions (L = C^∧N cyclometalated ligand). Accordingly, <b>1</b> and <b>2</b> exhibit structured emission bands which display a large involvement of ³LCCT (ligand-centered charge transfer) with lower contribution of ³MLCT (metal to ligand charge transfer) transition in the excited states. Also, biological activities of <b>1</b> and <b>2</b> were evaluated against three human cancer cell lines including A549 (human lung cancer), SKOV3 (human ovarian cancer), and MCF-7 (human breast cancer). <b>2a</b> presented an effective potent cytotoxic activity regarding to the cell lines. The cellular localization of <b>1a</b> and <b>2a</b> in MCF-7 human cells was investigated by fluorescence microscopy