Modulation of the conductance in platinum(ii) bis(acetylide) molecules through “gating” metal ions

Abstract

Mononuclear platinum(II) complex trans-Pt(PPh₃)₂(CCC₆H₄SMe-4)₂ (1-Pt) and its derivatives [PtM(dppm)₂(CCC₆H₄SMe-4)₂]⁺ (dppm = bis(diphenylphosphino)methane; M = Au, 2-PtAu; Ag, 2-PtAg; Cu, 2-PtCu) with “mono-gating” metal ions and [PtM₂(dpmp)₂(CCC₆H₄SMe-4)₂]²⁺ (dppm = bis(diphenylphosphinomethyl)phenylphosphine; M = Au, 3-PtAu₂; Ag, 3-PtAg₂) with “dual-gating” metal ions were elaborately designed to modulate the conductance in platinum(II) bis(σ-acetylide) complexes through “gating” d¹⁰ metal ions. The single-molecule conductance measurements by the STM-BJ technique demonstrate that the conductance follows 10^−4.5 (1-Pt) > 10^−4.8 (2-PtAu) > 10^−4.9 (2-PtAg) > 10^−5.0 (2-PtCu) > 10^−5.1 (3-PtAu₂) > 10^−5.3 (3-PtAg₂) G₀. Undoubtedly, charge transport along the platinum(II) bis(σ-acetylide) backbone is progressively restricted by introducing one to two “gating” M ions to the mononuclear platinum(II) molecule. As revealed by X-ray crystallography, the “gating” d¹⁰ metal ion is substantially bound to the acetylide and in fact the M–acetylide bonding is progressively enhanced in the order Au–C_acetylide → Ag–C_acetylide → Cu–C_acetylide, which coincides with a progressive decrease in the conductance as 10^−4.8 (2-PtAu) > 10^−4.9 (2-PtAg) > 10^−5.0 (2-PtCu) G₀. The M–acetylide coordination blocks the charge transport along the platinum(II) bis(σ-acetylide) backbone so that the d¹⁰ metal ion behaves as a resistor to suppress the conductance. Theoretical studies confirm that the “gating” metal ions control the HOMO energy, which is lowered by the increased d orbital contribution of “gating” metal ions through Pt–M interactions.