Experimental and computational magnetic resonance studies of selected rare earth and bismuth complexes

Abstract The rare-earth elements (REEs) and bismuth, being classified as the ‘most critical raw materials’ (European Raw Materials Initiatives, 2017), have a high economic importance to the EU combined with a high relative supply risk. REEs are highly important for the evolving technologies such as clean-energy applications, high-technology components, rechargeable batteries, permanent magnets, electric and hybrid vehicles, and phosphors monitors. This scientific research work aims at building a fundamental knowledge base concerning the electronic/molecular structure and properties of rare-earth element (REE) and bismuth complexes with dithiocarbamate (DTC) and 1,10-phenanthroline (PHEN) by employing state-of-the-art experimental techniques such as nuclear magnetic resonance (NMR) spectroscopy and X-ray diffraction (XRD) techniques together with ab initio quantum mechanical computational methods. This combination of methods has played a vital role in analysing the direct and significant effect of the heavy metal ions on the structural and magnetic resonance properties of the complexes, thereby, providing a framework of structure elucidation. This is of special importance for REEs, which are known to exhibit similar chemical and physical properties. The objectives of the work involve i) a systematic investigation of series of REE(III) as well as bismuth(III) complexes to get a profound understanding of the structure-properties relationship and ii) to find an appropriate theoretical modelling and NMR calculation methods, especially, for heavy metal systems in molecular and/or solid-state. This information can later be used in surface interaction studies of REE/bismuth minerals with DTC as well as in design and development of novel ligands for extraction/separation of metal ions. The REE(III) and bismuth(III) complexes with DTC and PHEN ligands have all provided a unique NMR fingerprint of the metal centre both in liquid and solid phase. The solid-state ¹³C and ¹⁵N NMR spectra of the diamagnetic REE(III) and bismuth(III) complexes were in accord with their structural data obtained by single crystal XRD. The density functional theory (DFT) methods were used to get complementary and refined structural and NMR parameters information for all diamagnetic complexes in the solid-state. The relativistic contributions due to scalar and spin-orbit correlations for the calculated ¹H/¹³C/¹⁵N chemical shifts of REE complexes were analysed using two-component zeroth-order regular approximation (ZORA)/DFT while the ‘crystal-lattice’ effects on the NMR parameters were calculated by combining DFT calculations on molecular and periodic solid-state models. The paramagnetic REE complexes display huge differences in their ¹H and ¹³C NMR spectral patterns. The experimental paramagnetic NMR (pNMR) chemical shifts, as well as the sizable difference of the ¹H and ¹³C NMR shifts for these isoelectronic complexes, are well reproduced by the advanced calculations using ab initio/DFT approach. The accuracy of this approach is very promising for further applications to demanding pNMR problems involving paramagnetic f-block elements. The results presented in this thesis demonstrate that a multidisciplinary approach of combined experimental NMR and XRD techniques along with computational modelling and property calculations is highly efficient in studying molecular complexes and solids containing heavy metal systems, such as rare-earths and bismuth

Structural investigations of rare earth dialkyl dithiocarbamate complexes: solid-state NMR, X-ray diffraction and DFT calculation studies

In this study, we made an attempt to qualitatively study the structures of few rare earth metal complexes by employing solid state NMR, X-Ray Diffraction, and preliminary DFT calculations. High resolution 13C and 15N solid state CP/MAS NMR spectra were recorded for six diamagnetic polycrystalline rare earth dialkyldithiocarbamates of the general formula [(RE2S2CNR2)3 PHEN] (where RE=La or Y, R=C2H5, C3H7, and i-C3H7) [1]. Different isotropic 13C and 15N chemical shifts for the three dialkyldithiocarbamato groups were observed. Regulacio et al. (2005) inferred that irrespective of the alkyl chains, rare earth complexes of dialkyldithiocarbamates and phenanthroline (3:1) ligands always crystallize in a monoclinic system with a space P21/c group. However, comparative analysis of solid state 13C/15N CPMAS spectra of polycrystalline yttrium and lanthanum diethyldithiocarbamate complexes shows the presence of significant differences, indicating structural variations of these complexes. Also, quite different X-Ray diffraction powder pattern was observed for the above two complexes. Finally, the computational geometry optimization of Y and La complexes, followed by the preliminary calculation of 13C and 15N chemical shifts and shielding contributions with the ADF program [2], found to be very near to the experimental results.Godkänd; 2013; Bibliografisk uppgift: [1] Regulacio MD, Tomson N, Stoll SL. Chemistry of materials, 2005, 17(12), 3114-3121. [2] Te Velde G, Bickelhaupt FM, Baerends EJ, et al. Journal of Computational Chemistry, 2001, 22(9), 931-967. ; 20130615 (vasgow)</p

Structural characterisation of amyloid-like fibrils formed by an amyloidogenic peptide segment of beta-lactoglobulin

Protein nanofibrils (PNFs) represent a promising class of biobased nanomaterials for biomedical and materials science applications. In the design of such materials, a fundamental understanding of the structure-function relationship at both molecular and nanoscale levels is essential. Here we report investigations of the nanoscale morphology and molecular arrangement of amyloid-like PNFs of a synthetic peptide fragment consisting of residues 11-20 of the protein beta-lactoglobulin (beta-LG(11-20)), an important model system for PNF materials. Nanoscale fibril morphology was analysed by atomic force microscopy (AFM) that indicates the presence of polymorphic self-assembly of protofilaments. However, observation of a single set of C-13 and N-15 resonances in the solid-state NMR spectra for the beta-LG(11-20) fibrils suggests that the observed polymorphism originates from the assembly of protofilaments at the nanoscale but not from the molecular structure. The secondary structure and inter-residue proximities in the beta-LG(11-20) fibrils were probed using NMR experiments of the peptide with C-13- and N-15-labelled amino acid residues at selected positions. We can conclude that the peptides form parallel beta-sheets, but the NMR data was inconclusive regarding inter-sheet packing. Molecular dynamics simulations confirm the stability of parallel beta-sheets and suggest two preferred modes of packing. Comparison of molecular dynamics models with NMR data and calculated chemical shifts indicates that both packing models are possible.Funding Agencies|Carl Tryggers stiftelse [CTS16:273, CTS18:810]; SeRC (Swedish e-Science Research Center)</p

Weathering of furan and 2,2′-bifuran polyester and copolyester films

Abstract Furan-based polymers are renewable alternatives for traditional fossil-based polymers, therefore carrying enormous potential for improved sustainability. Many aspects of these novel polymers still need to be investigated more comprehensively for full appreciation of their applicability. Here, the degradation of furan-based polymers including poly(butylene furanoate), poly(butylene bifuranoate), and three random copolyesters thereof were investigated under artificial weathering conditions for up to 300 h. This included simultaneous exposure of film samples to ultraviolet light, high humidity, and elevated temperature. Poly(ethylene terephthalate) was used as a reference material. Both the pristine and weathered samples were characterized using infrared spectroscopy, differential scanning calorimetry, and dynamic mechanical analysis, among others. According to the infrared measurements, the exposed surfaces of the films had undergone severe chemical changes. Indications of covalent cross-linking after exposure to ultraviolet light were found in differential scanning calorimetry, dynamic mechanical analysis, and dissolution experiments. The nature of the cross-linking mechanisms and exact structure of the formed degradation products remain unclear. It is concluded that polyesters derived from both 2,5-furandicarboxylic and 2,2′-bifuran-5,5′-dicarboxylic acids are relatively labile when exposed to UV light. The latter monomer appears especially labile, probably in part because of its broader and elevated UV absorbance. Simple oven-aging in air indicated that crosslinking also occurred in the absence of UV, but the overall chemical degradation was stronger in the weathering conditions. In the more easily crystallizable samples, the aging-induced crystallization played an important role in the final physical properties

Bi(III) complexes containing dithiocarbamate ligands:synthesis, structure elucidation by X‐ray diffraction, solid‐state ¹³C/¹⁵N NMR, and DFT calculations

Abstract We report on syntheses, characterisation by nuclear magnetic resonance (NMR) spectroscopy, X‐ray diffraction (XRD) measurements, and density functional theory (DFT) calculations of electronic/molecular structure and NMR chemical shifts of complexes of Bi(III), having the molecular formulae: [Bi{S₂CN(C₂H₅)₂)}₃] (1), [Bi{S₂CN(C₂H₅)₂)}₂(C₁₂H₈N₂)NO₃)] (2), and [Bi₂{S₂CN(CH₂)₅}₆ • H₂O] (3). The powder XRD patterns of complexes (1) and (2) resembled the corresponding calculated powder XRD patterns for previously reported single crystal structures. Single crystal XRD structure of complex (3), reported in this work, adopted an orthorhombic system with a space group Pbca with a=10.9956(3) Å, b=27.7733(8) Å, c=35.1229(10) Å and α=β=γ=90°. The experimental solid‐state ¹³C/¹⁵N NMR data of the complexes (1)‐(3) were in accord with their X‐ray single crystal structures. The unit cell of the complex (3) shows a weak supramolecular Bi···S interaction leading to the formation of a non‐centrosymmetric binuclear molecule [Bi₂{S₂CN(CH₂)₅}₆ • H₂O], which displays structural inequivalence in both ¹³C/¹⁵N NMR, and XRD data. Assignments of resonance lines in solid‐state ¹³C/¹⁵N NMR spectra of complexes (1)‐(3) were assisted by chemical shift calculations using periodic DFT methods. The findings of the present multidisciplinary approach will contribute in designing molecular models and further understanding of the structures and properties of (diamagnetic) metal complexes, including heavy metal ones

Structural insights into the polymorphism of bismuth(III) di-𝑛-butyldithiocarbamate by X-ray diffraction, solid-state (¹³C/¹⁵N) CP-MAS NMR and DFT calculations

Abstract Two crystalline polymorphs of a binuclear tris(di-𝑛-butyldithiocarbamato)bismuth(III) complex, I and II, with an empirical formula of [Bi{S₂CN(𝑛-C₄H₉)₂}₃] were synthesised and characterised by X-ray diffraction (XRD), solid-state NMR and density functional theory (DFT) calculations. At the supramolecular level, these mononuclear molecular units interact in pairs via secondary Bi⋯S bonds, yielding binuclear formations of [Bi₂{S₂CN(𝑛-C₄H₉)₂}₆]. The polymorph I (𝑃1̅) contains two isomeric non-centrosymmetric binuclear molecules of [Bi₂{S₂CN(𝑛-C₄H₉)₂}₆], which are related to each other as conformers, therefore having four structurally inequivalent bismuth atoms and twelve inequivalent dithiocarbamate ligands. In contrast, the structurally simpler polymorph II (𝑃2₁/𝑛) exists as a single molecular form of the corresponding centrosymmetric binuclear formation, comprising two structurally equivalent bismuth atoms and three structurally different dithiocarbamate groups. The polymorphs I and II were found to be interconvertible by altering the solvent system during the recrystallisation process. Sun et al. (2012) has reported a crystalline form of the title compound which resembles, but is not identical with, polymorph II. Experimental solid-state ¹³C and ¹⁵N cross-polarisation (CP) magic-angle-spinning (MAS) NMR spectra of both polymorphs I and II were in accord with the direct structural data on these complexes. Assignments of the resonance lines in the solid-state ¹³C and ¹⁵N NMR spectra were assisted by chemical shift calculations of the crystals using periodic DFT