Browsing by Author "Kozhemyakina, Nina V."

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Synthesis of new fullerides via the "break-and-seal" approach and their characterization
(2009) Kozhemyakina, Nina V.; Jansen, Martin (Prof. Dr.)
The present dissertation deals with the synthesis and characterization of fullerides. For the first time the "break-and-seal" technique was applied for fulleride synthesis. The reaction was performed in a completely all-glass apparatus under vacuum, avoiding the use of glass connections and use of grease. Starting from crown-ethers, potassium metal and C60 fullerene, six new fullerides have been synthesized. The modified "temperature difference method" was successfully used for growing single crystals from solution within a few days. In [K(DB24C8)(DME)]2C60*(DME) the fullerene unit has a charge of 2-. The (C60)2- units are arranged in hexagonal layers parallel to the ab plane, forming distorted trigonal prisms. The fullerene anions and potassium cations develop a pseudobinary topology which is reminiscent of the CdI2 structure type. Bond lengths' distribution in (C60)2- was examined. One orientation of the dianion was found to match perfectly the one predicted by calculations. KC60(THF)5*(THF)2 crystallizes in a structure with fully ordered C60 units. C60- anion-radicals and K+ form ion pairs. The ion pairs form corrugated layers in the ac crystallographic plane, the given compound being an example for a low-dimensional fulleride partial structure. For the compound [K(DB24C8)(THF)]2C60*THF the structure solution was complicated by the disorder of crown-ether and solvent molecules which could not be overcome, although the (C60)2- unit was ordered. In [K(DB24C8)(DME)]C60 the fullerene unit exists as a monomeric anion-radical and in [K(DB24C8)(DME)]2[C60]2 - as a dimer-dianion. The latter compound is an example of rather not many fulleride structures, where C60 exists in the form of dimers. The interfullerene C-C bond length is 1.57(3) Å. In [4{K(DB18C6)(C60-)}(THF)6]*[C60]*(THF)6 at temperatures above 220 K each of the four C60- units exists in form of anion-radicals, and at lower temperatures - as a dimer-dianion, the interfullerene bond being 1.63(0) Å. The dimers are fully ordered. In addition, uncharged disordered C60 molecules are found, what follows from the charge balance. The low-temperature phase is a first example of a fulleride structure where fullerene exists in three different bonding states: anion-radical monomer, dianion-dimer, and a neutral C60. In the dimer, the pentagons adjacent to sp3-hybridized carbon atoms, are in trans-conformation. DFT calculations were performed, and it is now for the first time that a localization of the negative charge on a small fragment of the C60 cage was found out. Knowing this, it becomes conclusive, considering the Coulombic repulsion, that the preferred orientation of two bound C60- units is trans-conformation. Magnetic measurements were performed. The method for fulleride synthesis used in the present work has a big potential for broadening by using different metals (e.g. alkali, alkali-earth), varying the complexing agents (crown-ethers, cryptands), as well as the organic solvent (or solvent mixtures).