Structural and Luminescent Changes as a Function of Copper(I) Ligation
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Authors
Brown, Thomas W.
Issue Date
2016
Type
Dissertation
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Abstract
This dissertation investigates the modulation of copper(I) luminescence as a function of cuprophilicity, coordination environment, and mixed metallophilic interactions. Chapter 2 reports a simple bis(copper) compound supported by bridging phosphine ligands. The compound is prepared by a simple ligand substitution reaction between [Cu(MeCN)4]PF6 and bis(diphenylphosphino)methane. [Cu2(dppm)2(MeCN)4](PF6)2 (2.8) is non-emissive to the naked eye, but upon loss of two coordinated acetonitrile molecules under heat, vacuum, or grinding forms a bright blue luminescent material which is identified as [Cu2(dppm)2(MeCN)2](PF6)2 (2.9). Compounds 2.8 and 2.9 can be interconverted by the loss or addition of acetonitrile molecules, and this interconversion can be followed by emission spectroscopy. Upon recrystallization from wet solvent, hydrolysis of a PF6- anion occurs in both compounds 2.8 and 2.9 to produce a different blue luminescent species identified as [Cu2(dppm)2(PO2F2)]PF6 (2.10). A cuprophilic interaction between the copper ions of both compounds 2.9 and 2.10 is responsible for the emission under UV illumination. In chapter 3, the luminescence of a series of three-coordinate copper(I) compounds with pyridyl derivatives is reported. [Cu(PCy3)2]PF6 (3.10) readily coordinates pyridine to form [Cu(pyr)(PCy3)2]PF6 (3.11), deuterated pyridine to form [Cu(d5pyr)(PCy3)2]PF6 (3.12), piperidine to form [Cu(pip)(PCy3)2]PF6 (3.13), 4-picoline to form [Cu(pic)(PCy3)2]PF6 (3.14), 4-dimethylaminopyridine to form [Cu(DMAP)(PCy3)2]PF6 (3.15), 4-bromopyridine to form [Cu(Brpyr)(PCy3)2]PF6 (3.16), 3,5-difluoropyridine to form [Cu(F2pyr)(PCy3)2]PF6 (3.17), quinoline to form [Cu(quin)(PCy3)2]PF6 (3.18), and isoquinoline to form [Cu(isoquin)(PCy3)2]PF6 (3.19). [Cu(PCy3)2]PF6 (3.10) also coordinates bis(azacycles) in a two-to-one stoichiometry to generate bis(copper) species. [Cu(PCy3)2]PF6 (3.10) reacts with pyrazine to form [{Cu(PCy3)2}2(pyrz)](PF6)2 (3.20), 4-cyanopyridine to form [{Cu(PCy3)2}2(CN-pyr)](PF6)2 (3.21), and 4,4’-bipyridine to form [{Cu(PCy3)2}2(bpy)](PF6)2 (3.22). Compounds 3.11-3.22, with the exception of compound 3.13, are emissive under UV illumination. This emission is the result of a metal-to-ligand charge transfer (MLCT) process. Substituting electron donating and electron withdrawing group on the pyridine modulates the energy of the LUMO and alters the emission. Computational studies were performed to model the MLCT process by modulating the HOMO and LUMO of simple three-coordinate copper(I) compounds. The P-Cu-P angle was expanded and contracted to perturb the HOMO while modifying pyridyl substituents perturbed the LUMO. In chapter 4, a series of gold-copper bimetallic compounds containing asymmetric N-heterocyclic carbene (NHC) ligands were synthesized. Ag2O reacts with [H(pyCH2imCH3)]PF6, [H(pyCH2CH2imCH3)]PF6, and [H(pyCH2benzimCH3)]PF6 in a 0.25 equivalent to 1 equivalent stoichiometry to produce [Ag(pyCH2imCH3)2]PF6 (4.8), [Ag(pyCH2CH2imCH3)2]PF6 (4.11), and [Ag(pyCH2imCH3)2]PF6 (4.14) respectively. The addition of one equivalent of gold(tetrahydrothiphene)chloride to compounds 4.8, 4.11, and 4.14 produces [Au(pyCH2imCH3)2]PF6 (4.9), [Au(pyCH2CH2imCH3)2]PF6 (4.12), and [Au(pyCH2imCH3)2]PF6 (4.15) through a transmetallation reaction. The addition of one equivalent of [Cu(MeCN)4]PF6 to compounds 4.9, 4.12, and 4.15 readily produces [Au(pyCH2imCH3)2Cu(MeCN)2](PF6)2 (4.10), [Au(pyCH2CH2imCH3)2Cu](PF6)2 (4.13), and [Au(pyCH2benzimCH3)2Cu(MeCN)2](PF6)2 (4.16) respectively. Compounds 4.10, 4.13, and 4.16 are highly emissive in the solid-state under UV illumination. The luminescence is most likely the of a Cu d → π* transition. Surprisingly, these compounds do not display interesting mechanochromism or vapochromism. A solvent-free crystal structure of compound 4.16 does display an intramolecular metallophilic interaction between the gold and copper ions. The crystal structure of solvated compound 4.13 displays an intermolecular aurophilic interaction between the gold ions of different cations occupying the asymmetric unit. The spectroscopy, X-ray crystallography, and thermogravimetric analysis for compounds 4.10, 4.13, and 4.16 is discussed.
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