Chemistry, Physics & Earth Sciences

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Browsing Chemistry, Physics & Earth Sciences by Subject "195Pt NMR"
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    Octupolar organometallic Pt(II) NCN-pincer complexes; Synthesis, electronic, photophysical, and NLO properties
    (Elsevier, 2017-12-28) Batema, Guido D ; van Walree, Cornelius A ; van Klink, Gerard P M ; de Mello Donega, Celso ; Meijerink, Andries ; Perez-Moreno, Javier ; Clays, Koen ; van Koten, Gerard
    A series of organometallic octupolar 1,3,5-substituted-2,4,6-styryl-benzene complexes was synthesized by post-modification of parent [PtCl(NCN-CHO-4)], i.e. 1,3,5-tri-R-2,4,6-tris[(4-(PtCl)(3,5-bis[(dimethylamino) methyl]styryl)]benzene (NCN ¼ [C6H2(CH2NMe2)2-2,6]e in which R ¼OMe, H, Br (1e3). Their synthesis involved a triple Horner-Wadsworth-Emmons reaction of [PtCl(NCN-CHO-4)] with the appropriate tris[(diethoxyphosphoryl)]methyl]benzene derivative. The 195Pt{1H} NMR chemical shift reflects the electronic properties of the p-system to which it is connected. The UV/Vis bands of the octupolar platinum complexes are only slightly red-shifted (by 5e12 nm) with respect to those of corresponding stilbenoid Pt-Cl pincer compounds (i.e., the separate branches), suggesting that there is only a limited electronic interaction between these branches. The fluorescence Stokes shift, quantum yields and lifetimes of 1e3 also are of the same order of magnitude as those of stilbenoid Pt-Cl pincer compounds, indicating that a dipolar excited state is formed, which is localized on one of the three branches. The hyper-Rayleigh scattering technique revealed hyperpolarizabilites bHRS of 430, 870 and 183 10 30 esu for 1, 2 and 3, respectively, which are among the highest for transition metal complexes. The highest value was found for the compound lacking a donor or acceptor group at the central core, lending support to the idea that dispersion overwhelms charge transfer in determining the magnitude of the first hyperpolarizability in octupolar compounds.