Elektrostatička svojstva atoma sumpora u derivatima tiosemikarbazida

Abstract

U ovoj doktorskoj disertaciji izloženi su rezultati analize eksperimentalno i teorijski dobijene raspodele gustine naelektrisanja dva derivata tiosemikarbazida, 4-metil-3-tiosemikarbazida (MeTSC) i 4-metil-3-tiosemikarbazon 2-piridinformamida (TSC4). Analiza eksperimentalno dobijene gustine naelektrisanja je zasnovana na preciznim podacima dobijenim difrakcijom rendgenskog zračenja visoke rezolucije. Teorijska istraživanja bazirana su na teorijskim strukturnim faktorima dobijenim primenom programa CRYSAL09 polazeći od geometrije molekula određene nakon multipol utačnjavanja eksperimentalno dobijene gustine naelektrisanja. Za opisivanje eksperimentalne i teorijske ukupne elektronske gustine korišćen je Hansen-Coppens-ov multipol-model. Takođe je urađena i topološka analizahemijskih veza i interakcija i ispitivana su elektrostatička svojstva atoma sumpora. Analizom eksperimentalne gustine naelektrisanja kristalnih struktura MeTSC i TSC4 uočeno je da deformaciona gustina slobodnih elektronskih parova S atoma ima oblik torusa, da je unutar njega raspodela elektronske gustine nehomogena i da položaj samog torusa može biti ortogonalan (SalTSC) ili pod uglom (MeTSC, TSC4). Na osnovu raspodele deformacione gustine i elektrostatičkog potencijala, kao i na osnovu topološke analize ukupne eksperimentalne gustine naelektrisanja ρktv i njenog Laplasijana ∇2ρktv zaključeno je da atom sumpora ima izrazitu fleksibilnost i sposobnost da prilagodi svoju elektronsku gustinu slobodnih elektronskih parova prostornom rasporedu donornih grupa koje učestvuju u interakcijama sa S akceptorom. U kristalnim strukturama MeTSC i TSC4 utvrđeno je da S atom istovremeno gradi četiri, odnosno prosečno šest međumolekulskih interakcija. U cilju upotpunjavanja eksperimentalnih rezultata analizirana je teorijski dobijena gustina naelektrisanja oba molekula, a zatim su ispitivane karakteristike sumpora kao akceptora i to u sistemima različite složensti polazeći od izolovanih monomera, preko izdvojenih dimer do kristalnogokruženja. Ovom analizom je utvrđeno da se simultanim angažovanjem S atoma u više interakcija ne umanjuje njegova akceptorska sposobnost. Vodonične vezekoje uključuju S akceptor su ispitivane sa aspekta energijskih svojstava dimera koji suprisutni u MeTSCi TSC4, kaoi u dodatno konstruisanim sistemima MeTSC/MeOH i aceton/MeOH. Energijske karakteristike su proučavane u pogledu elektrostatičke energije interakcije (Ees) i kohezione energije(Ecoh). Za dva odabrana MeTSC/MeOH i aceton/MeOH sistema je primenjena metoda kuplovanih klastera kaošto je ab initio CCSD(T) metod. Za MeTSC/MeOH sistem je urađena potpuna optimizacija i za tako dobijenu ravnotežnu geometriju je izračunata energija sistema ∆ECCSD(T),CBS.

In this dissertation the analysis of the experimental and theoretically obtained electron density of two derivatives of thiosemicarbasides, 4-methyl-3-thiosemicarbaside (MeTSC) and 4-methyl-3-thiosemikabazone 2-piridinformamide (TSC4) are presented. The analysis of experimentally obtained electron density is based on accurate X-ray diffraction data of high resolution. Theoretically calculated electron densities are obtained from periodic quantum mechanical calculation using CRYSTAL09 and the accurate structural parameters from high resolution X-ray experiment. For the description of the theoretical and experimental electron density the Hansen-Coppens multipol model was used. Further topological analysis of chemical bonds and interactions was performed in order to explain the electrostatic properties of sulfur. In this work it has been observed that in the experimentally obtained electron density of the MeTSC and TSC4 crystal structures, the deformational electron density of sulfur free electron pairs forms a toroidal shape. Further, this torus is not homogeneously filled but shows pronounced local accumulations and its position can be either orthogonal (like in SalTSC) or tilted (MeTSC, TSC4). Based on the distribution of the deformational electron density and electrostatic potential, as well as the topological analysis of the total electron density ρktv and its Laplasian ∇2ρktv it can be concluded that the S atom has a remarkable flexibility and ability to adapt his deformation electron density of free electron pairs into toruses corresponding to the position of donor groups surrounding him. In the crystal structures of MeTSC and TSC4 it was determined that the S atom participates in four and six interactions, respectively. In order to supplement the experimentally obtained results a theoretically calculated electron density of both molecules (MeTSC and TSC4) was performed and the properties of the S atom as a hydrogen acceptor have been studied. The analysis was performed on systems of various complexity, starting with isolated monomers, then on dimers and up to the whole crystal packing. From this work it has been concluded that the acceptor capabilities of the S atom are not diminished with the increasing number of interactions. The hydrogen bonding involving thioureido S acceptor is also investigated in terms of the energetic properties of the MeTSC and TSC4 dimers existing in the crystal structure, and additional MeTSC/MeOH and acetone/MeOH systems. Energetic features were thoroughly studied through electrostatic interactions energies (Ees) and cohesive energies (Ecoh). For two selected MeTSC/MeOH and acetone/MeOH systems an ab initio approach employing the coupled-cluster singles and doubles augmented by a perturbational correction for connected triple excitations (CCSD(T)) method were applied. Finaly, for MeTSC/MeOH system full geometry optimization was performed and for resulting equilibrium geometry the energy of the system (∆ECCSD(T),CBS) was calculated.