| Popis: |
Za potrebe ovoga rada pripravljen je N-(2-karboksifenil)glicin – dikiselina s karboksil-nim skupinama na aromatskom i alifatskom dijelu molekule, a kristalizacijom iz otopine pri-pravljeni su kristali binarnih krutina dikiseline s petnaest piridinskih derivata. Dobivene su kru-tine strukturno i termički okarakterizirane difrakcijom rentgenskog zračenja na jediničnom kri-stalu, difrakcijom rentgenskog zračenja na praškastom uzorku, razlikovnom pretražnom kalo-rimetrijom i termogravimetrijskom analizom. U jedanaest krutina uočeno je preferencijalno po-vezivanje piridina i alifatske karboksilne skupine. Analizom geometrija vodikovih veza te izra-čunatih naboja i elektrostatskih potencijala pronađeno je da je alifatska karboksilna skupina bolji donor vodikove veze od aromatske. Sve duljine vodikovih veza u kojima sudjeluje alifat-ska karboksilna skupina uglavnom slijede empirijsko pravilo temeljeno na razlici vrijednosti pKa odgovarajućih piridinskih derivata i karboksilne skupine. Prijenos protona s karboksilne kiseline na piridinski dušik uočen je u jedanaest struktura (pri čemu su nastale soli), dok su preostale četiri krutine kokristali. Uočeno je da prijenos protona ima bitan utjecaj na pakiranje u kristalu: u kokristalima molekule su povezane u diskretne molekulske komplekse, dok su u solima pronađeni lanci monoaniona kao glavni motiv povezivanja. Within this master thesis, N-(2-carboxyphenyl)glycine − a carboxylic acid with carboxyl groups on aromatic and aliphatic part of the molecule has been synthesized. Its binary solids single crystals with fifteen pyridine derivatives have been prepared by crystalization from so-lution. Obtained compounds were structuraly and thermally characterized by single crystal and powder X-ray diffraction, differential scanning calorimetry and thermogravimetric analysis. In eleven obtained compounds preferentially binding of pyridine nitrogen and aliphatic carboxyl group has observed and it was found that this carboxyl group is a better hydrogen bond donor than aromatic carboxyl group, what is explained by hydrogen bond geometries and calculated NBO charges and electrostatic potentials of carboxyl hydrogen atoms. All noticed hydrogen bond lenghts on aliphatic carboxyl group follows empirical „pKa rule”. Proton transfer from carboxyl group to pyridine nitrogen was observed in eleven compounds leading to formation of salts, while the remaining four are co-crystals. It was also observed that the proton transfer has considerable effect on the crystal packing: in co-crystals molecules are linked into a discrete molecular complexes, while in salts chains of monoanions are observed as the main packing motif. |
