A Luminescent Platinum(II) 2,6-Bis(N-pyrazolyl)pyridine Complex

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Abstract
Four platinum(II) cationic complexes were prepared with the mer-coordinating tridentate ligands 2,6-bis(N-pyrazolyl)pyridine (bpp) and 2,6-bis(3,5-dimethyl-N-pyrazolyl)pyridine (bdmpp): [Pt(bpp)Cl]Cl·H2O; [Pt(bdmpp)Cl]Cl·H2O; [Pt(bpp)(Ph)](PF6); [Pt(bdmpp)(Ph)](PF6). The complexes were characterized by 1H NMR spectroscopy, elemental analysis, and mass spectrometry, and the structures of the bpp derivatives were determined by X-ray crystallography. [Pt(bpp)Cl]Cl·2H2O: monoclinic, P21/n, a = 11.3218(5) Å, b = 6.7716(3) Å, c = 20.6501(6) Å, β = 105.883(2)°, V = 1522.73(11) Å3, Z = 4. The square planar cations stack in a head-to-tail fashion to form a linear chain structure with alternating Pt···Pt distances of 3.39 and 3.41 Å. [Pt(bpp)(Ph)](PF6)·CH3CN: triclinic, P1̄, a = 8.3620(3) Å, b = 10.7185(4) Å, c = 13.4273(5) Å, α = 96.057(1)°, β = 104.175(1)°, γ = 110.046(1)°, V = 1072.16(7) Å3, Z = 2. Cyclic voltammograms indicate all four complexes undergo irreversible reductions between −1.0 and −1.3 V vs Ag/AgCl (0.1 M TBAPF6/CH3CN), attributable to ligand- and/or metal-centered processes. By comparison to related 2,2‘:6‘,2‘ ‘-terpyridine complexes, the electrochemical and UV−visible absorption data are consistent with bpp being both a weaker σ-donor and π-acceptor than terpyridine. Solid samples of [Pt(bpp)(Ph)](PF6) at 77 K exhibit a remarkably intense, narrow emission centered at 655 nm, whereas the other three complexes exhibit only very weak emission.