Chemistry of Low-Valent Platinum Dimers

Citation

Zietlow, Miriam Heinrichs (1989) Chemistry of Low-Valent Platinum Dimers. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/j4bj-3046. https://resolver.caltech.edu/CaltechTHESIS:10282013-161114555

Abstract

Physical and chemical properties of low-valent platinum dimers, namely [Pt₂(P₂O₅H₂)₄]⁴⁻ and Pt₂(µ-dppm)₂Cl₂, have been investigated using a variety of structural and spectroscopic techniques.

Platinum(II) d⁸-d⁸ dimers have been shown to exhibit much thermal and photochemical reactivity. Chapter 2 describes studies aimed at elucidating the excited state reduction potenetial of [Pt₂(P₂O₅H₂)₄]⁴⁻, Pt₂, in organic media. By conducting excited state electron transfer studies using derivatized pyridiniums and benzophenones, the excited state reduction potential has been estimated to be ~2 V. The Pt₂ complex undergoes partial oxidation to form Pt(II,III) linear chains. Chapter 3 describes the structural and spectroscopic techniques used to determine the translational symmetries of these [Pt₂(P₂O₅H₂)₄]⁴⁻ (X = Cl, Br), Pt₂X, chains. Pt₂Br has been found to be intermediate between (AAB)ₙ and (AABCCB)ₙ, while, Pt₂Cl is of (AABCCB)ₙ translational symmetry. Investigations into the electronic transitions of Pt₂Cl and Pt₂Br were conducted using high pressure techniques and are presented in Chapter 4. The Pt₂X electronic spectrum exhibits bands attributable to the reduced Pt₂ complex and the oxidized Pt₂X₂ complex ([Pt₂(P₂O₅H₂)₄X₂]⁴⁻) along with an intervalence charge-tranfer band characteristic of a mixed-valence solid.

Photophysical investigations of a new luminescent chromophore, Pt₂(µ-dppm)₂Cl₂, a d⁹-d⁹ dimer, and its analogs are described in Chapter 5. The absorption band directly responsible for the observed emission is believed to be very weak and, as of yet, unobserved. Attempts to determine the spin multiplicty and approximate energy of this unobserved transition are described in Chapter 6. Excited-state energy transfer studies indicate that this absorption band is a triplet transition at -13,000 cm⁻¹. Although, the Pt₂(µ-dppm)₂Cl₂ excited state is non-luminescent in fluid solution, it has been shown to undergo thermal electron transfer to tetracyanoethylene and photoinduced electron transfer to methylviologen. These experiments are presented in Chapter 7. Preliminary studies, described in Chapter 8, of non-bridged d⁹-d⁹ platinum(I) dimers have shown that [Pt₂(CNCH₃)₆]²⁺ serves as a versatile precursor in the synthesis of new d⁸-d⁸ A-frame complexes.

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