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The work presented in this dissertation focuses on platinum(II) and platinum(IV) complexes with the 2,6-bis(N-methylbenzimidazol-2'-yl)pyridine (mbzimpy) pincer ligand. The complexes have the general formulae Pt(mbzimpy)X+ (X: Cl, Br, CCPh, Ph and CH3) and Pt(mbzimpy)X3+) (X: Cl, Br). The second chapter details the investigations of electronic structures of Pt(mbzimpy)X+ complexes using cyclic voltammetry, UV-visible and emission spectroscopies. The Pt(tpy)X+ analogs (tpy= 2,2’;6’2”-terpyridine) have also been examined for comparison. Pt(L)X+ complexes (L: mbzimpy or tpy) undergo two chemically reversible one-electron reduction processes at cathodic potentials. In the case of Pt(mbzimpy)X+, these processes occur at slightly more negative potentials. Furthermore, these processes are shifted cathodically along the Cl〈CCPh〈Ph〈CH3 series of ancillary ligands. The absorption spectra of Pt(L)X+ exhibit ligand-centered (1LC) transitions (ε ≈ 104 M-1cm-1) in the UV region and metal-to-ligand-charge transfer (1MLCT) transitions (ε ≈ 103 M-1cm-1) in the visible region. The corresponding visible band in Pt(L)(CCPh)+ has been assigned to the 1 (LLCT/MLCT) mixed state (LLCT: ligand-to-ligand-charge transfer). The preceding 1LC and 1MLCT transitions of Pt(mbzimpy)X+ occur at longer wavelengths than found for the corresponding Pt(tpy)X+ analogs. The 1MLCT band of Pt(L)X+ is shifted to the red along Cl〈Ph〈CH3 series. The low energy 1LC states of Pt(mbzimpy)X+ occur at virtually the same wavelength, whereas they undergo a distinct shift to the blue along Cl〈Ph〈CH3 series in the case of Pt(tpy)X+. The latter effect has been qualitatively explained by invoking ϖ* (L)/6pz(Pt) orbital mixing. The frozen solutions of all the compounds exhibit structured emission beginning at λmax in the 470-560 nm range. This emission is assigned to the 3LC state which is stabilized due to configurational interaction with the higher-lying 3MLCT state. In the case of Pt(L)CCPh+, the emission, however, originates from a 3(LLCT/MLCT) mixed state.Chapter 3 describes an investigation of the aggregation of Pt(mbzimpy)(CH3)+ and Pt(tpy)(CH3)+ in DMSO-d6 using 2D 1H-1H NOESY, as well as concentration-dependent 1H NMR and UV-visible absorption spectroscopies. A detailed analysis of NMR and UV-visible spectra leads to the conclusion that both compounds form head-to-tail dimers in DMSO solution. Further, it is evident that the forces stabilizing these dimers are dominated by ligand..ligand interactions. The intermolecular interactions stabilizing dimers of Pt(mbzimpy)(CH3)+ are decidedly stronger than those of the terpyridyl analog.Chapter 4 details the first successful isolation and characterization of Pt(mbzimpy)X3+ (X = Cl and Br ) salts. Electrochemical studies show that these complexes undergo an irreversible reduction accompanied by loss of axial halide ligands. Pt(mbzimpy)Cl3+ is slightly more stable to reduction than the corresponding bromo complex. No emission was observed from the bromo derivative, whereas 77K frozen solutions of Pt(mbzimpy)Cl3+ shows extremely weak emission near 690nm. The latter emission is tentatively assigned as originating from a lowest 3LF state. |
