I-M-I...I-M-I interactions in transition metal complexes

Elgadi, Gamra Mohamed (2016-03)

Thesis (MSc)--Stellenbosch University, 2016

Thesis

ENGLISH ABSTRACT : A theoretical study of iodine to iodine (I⋯I) interactions within dimers of transition metal-iodide complexes was performed utilizing the Cambridge Structural Database (CSD) and computational methods. A comprehensive analysis of the I⋯I interactions among previously published experimental crystal structures of metal-iodide complexes included in the CSD was first carried out. The CSD search initially identified all complexes containing the I–M–I moiety in the solid state, where M is a transition metal and I is an iodine atom, and then determined all complexes exhibiting I⋯I interactions to form dimers of I–M–I....I–M–I motifs. The analysis revealed that complexes containing copper (Cu), mercury (Hg), gallium (Ga), silver (Ag), platinum (Pt), palladium (Pd) or bismuth (Bi) are the most likely to undergo such I⋯I interactions. The complexes exhibited different types of I⋯I intermolecular contacts including single, double, multiple and bifurcated interactions. The crystal structures of these complexes were then visualized and analyzed to determine the most common orientations (i.e., conformations) of the two I–M–I moieties relative to each other. The most common conformations of these interactions in the solid state were found to be chair, boat, bent, >...<– shaped and zigzag forms. Shorter distances between I atoms (indicative of stronger interactions) are most likely to occur when the relative orientation of the two I–M–I moieties is in the chair form, with average distances ranging between 3.4 and 3.8 Å. The nature and strength of the I⋯I intermolecular interactions in dimers of some selected transition metal-iodide complexes (containing Cu, Hg, Ga, Ag, Pt, Pd or Bi) were also investigated by means of Density Functional Theory (DFT). Calculations were performed in the gas phase and in an implicit solvent model using different solvents with a wide range of dielectric constants (water, ethanol and chloroform). Various levels of DFT, namely PBEPBE/aug-cc-pVTZ-pp/6-31G(d), B3LYP/LANL2DZ and B3LYP/aug-cc-pVTZ-pp/6-31G(d) were used. Optimizations in different environments using an implicit polarizable continuum solvent model showed that there was a significant dependence of the I⋯I interaction energy (EINT) and distance on the electrostatic environment in which the complex is found. As the dielectric constant increases the EINT increases significantly, while the I⋯I intermolecular distance decreases considerably. The I⋯I interactions were also studied by the natural bond orbital (NBO) and the Atoms in Molecules (AIM) analyses to determine their nature and properties. NBO analysis does not confirm the existence of an I⋯I bond within dimers of metal-iodide complexes in the gas phase or an implicit solvent model. There was no evidence of electron transfer between iodine atoms in the I⋯I moiety, indicating that the two fragments in the dimers are connected only via dispersion interactions. Since the transition metal-iodide complexes do not form stable dimers in the gas phase it was only possible to obtain AIM parameters (i.e., ρb, L(ρb), and Hb) for the I⋯I interaction in a solvent. These were shown to depend on the electrostatic environment (i.e., dielectric constant of the solvent), such that, in general, an increase in the dielectric constant resulted in a significant increase in the calculated values of AIM parameters corresponding to stronger interactions.

AFRIKAANSE OPSOMMING : 'n Teoretiese studie van jodium tot jodium (I ⋯ I) interaksies binne dimere van oorgangsmetaal-jodied komplekse is met behulp van die "Cambridge Structural Database" (CSD) en berekeningsmetodes uitgevoer. 'n Omvattende ontleding van die I ⋯ I interaksies tussen voorheen gepubliseerde eksperimentele kristalstrukture van metaal-jodied komplekse uit die CSD is vir die eerste keer uitgevoer. Die CSD soektog het aanvanklik alle komplekse met die I-M-I eenheid, waar M 'n oorgangsmetaal en I is 'n jodium atoom is, in die vaste toestand geïdentifiseer, waarna alle komplekse wat I ⋯ I interaksies ondergaan om dimere met die I-M-I⋯ I-M-I motief te vorm bepaal is. Hierdie ontleding het getoon dat komplekse met koper (Cu), kwik (Hg), gallium (Ga), silwer (Ag), platinum (Pt), palladium (Pd) en bismut (Bi) mees waarskynlik I ⋯ I interaksies vorm. Die komplekse het verskillende tipes I ⋯ I intermolekulêre kontakte getoon insluitende enkel-, dubbel-, veelvoudige- en vertakte-interaksies. Die kristalstrukture van hierdie komplekse is toe gevisualiseer en ontleed om die mees algemene oriëntasies (dws, konformasies) van die twee I-M-I eenhede relatief tot mekaar te bepaal. Dit is gevind dat die mees algemene konformasies van hierdie interaksies in die vaste toestand die stoel, boot, gebuigte, > ⋯ < en sigsag vorme is. Korter afstande tussen I atome (aanduiding van sterker interaksies) is die meeste geneig om voor te kom wanneer die relatiewe oriëntasies van die twee I-M-I eenhede in die stoel vorm is, met gemiddelde afstande wat tussen 3,4 en 3,8 Å wissel. Die aard en sterkte van die I ⋯ I intermolekulêre interaksies in dimere van sommige gekose oorgangsmetaal-jodied komplekse (met Cu, Hg, Ga, Ag, Pt, Pd en Bi) is ook ondersoek deur middel van Digtheid Funksionele Teorie (DFT). Berekeninge is uitgevoer in die gasfase en in 'n implisiete oplosmiddelmodel met verskillende oplosmiddels met 'n wye verskeidenheid van diëlektriese konstantes (water, etanol en chloroform). Verskillende vlakke van DFT, naamlik PBEPBE/aug-cc-pVTZ-pp/6-31G(d), B3LYP/LANL2DZ en B3LYP/aug-cc-pVTZ-pp/6-31G(d) is gebruik. Optimisering in verskillende omgewings deur middel van 'n implisiete polariseerbare kontinuum oplosmiddelmodel het getoon dat daar 'n beduidende afhanklikheid van die I⋯ I interaksie energie (EINT) en afstand op die elektrostatiese omgewing waarin die kompleks gevind is. Namate die diëlektriese konstante verhoog sal die EINT ook aansienlik verhoog, terwyl die I ⋯ I intermolekulêre afstand gelyktydig verminder. Die I ⋯ I interaksies is ook deur die "Natural Bond Orbital" (NBO) en "Atoms in Molecules" (AIM) metodes geanaliseer om hulle aard en eienskappe te bepaal. NBO ontleding kon die bestaan van 'n I ⋯ I binding binne dimere van metaal-jodied komplekse in die gasfase of 'n implisiete oplosmiddelmodel nie bevestig nie. Daar was geen bewyse van elektronoordrag tussen jodium atome in die I ⋯ I eenheid, wat daarop aandui dat die twee fragmente in die dimere slegs deur dispersie-interaksies verbind is. Omdat die oorgangsmetaal-jodied komplekse nie stabiele dimere in die gasfase gevorm het nie was dit slegs moontlik om AIM parameters (dws, ρb, L(ρb), en Hb) vir die I ⋯ I interaksie in 'n oplosmiddel te bereken. Dit is aangetoon dat hierdie waardes afhanklik van die elektrostatiese omgewing (dit wil sê, diëlektriese konstante van die oplosmiddel) is, sodanig dat, oor die algemeen, 'n toename in die diëlektriese konstante tot 'n beduidende toename in die berekende waardes van AIM parameters gelei het wat met sterker interaksies ooreenstem.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/98654
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