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Tris Pyrazolyl Borate Synthesis Essay

Abstract

A new cyanoscorpionate - tris(4-cyano-3,5-diphenylpyrazolyl)borate (TpPh2,4CN) has been synthesized and characterized. The thallium complex of this ligand TlTpPh2,4CN has also been prepared and characterized by FT-IR, 1H NMR, and single-crystal X-ray-diffraction. The complex TlTpPh2,4CN crystalized in the monoclinic space group C2/c with unit cell a = 14.6697(10) Å, b = 13.9493(10) Å, c = 19.3347(12) Å, and b= 91.761(2)°. Structural comparison of TlTpPh2,4CN with analogous complexes demonstrated the effects of both steric and electron-withdrawing substituents on coordination geometry and the electronic properties of the metal ion. There were short contacts between the cyano groups and neighboring thallium ions that also indicated the ligand’s potential to form coordination polymers.

Document Type

Thesis - Open Access

Recommended Citation

Som, Bozumeh, "Synthesis and Characterization of a New Cyano-substituted Tris(pyrazolyl)borate and its Thallium(I) Complex" (2013). Electronic Theses and Dissertations. Paper 2273. https://dc.etsu.edu/etd/2273

Copyright

Copyright by the authors.

Abstract

Reaction of [Si(3,5-Me2pz)4] (1) with [Cu(MeCN)4][BF4] (2) gave the mono- and dinuclear copper complexes [Cu2(FTp*)2] (3) and [Cu(FTp*)2] (4). Both complexes contain the so-far unprecedented boron-fluorinated FTp* ligand ([FB(3,5-Me2pz)3] with pz=pyrazolyl) originating from 1, acting as a pyrazolyl transfer reagent, and the [BF4] counter anion of 2, serving as the source of the {BF} entity. The solid-state structures as well as the NMR and EPR spectroscopic characteristics of the complexes were elaborated. Pulsed gradient spin echo (PGSE) experiments revealed that 3 retains (almost entirely) its dimeric structure in benzene, whereas dimer cleavage and formation of acetonitrile adducts, presumably [Cu(FTp*)(MeCN)], is observed in acetonitrile. The short Cu⋅⋅⋅Cu distance of 269.16 pm in the solid-state is predicted by DFT calculations to be dictated by dispersion interactions between all atoms in the complex (the Cu−Cu dispersion contribution itself is only very small). As revealed by cyclic voltammetry studies, 3 shows an irreversible (almost quasi-reversible at higher scan rates) oxidation process centred at Epa=−0.23 V (E01/2=−0.27 V) (vs. Fc/Fc+). Oxidation reactions on a preparative scale with one equivalent of the ferrocenium salt [Fc][BF4] (very slow reaction) or air (fast reaction) furnished blue crystals of the mononuclear copper(II) complex [Cu(FTp*)2] (4). As expected for a Jahn–Teller-active system, the coordination sphere around copper(II) is strongly distorted towards a stretched octahedron, in accordance with EPR spectroscopic findings.

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