| 1. |
- Bredyuk, O.A., et al.
(author)
-
Three-Dimensional Polymeric Thallium(I) Morpholinedithiocarbamate [Tl2{S2CN(CH2)4O}2]n and Its Capability of Binding Gold(III) from Solutions : Chemisorption Synthesis of a Heteronuclear Gold(III)–Thallium(III) Complex of the Ionic Type, ([Au{S2CN(CH2)4O}2][TlCl4])n, the Role of Secondary Interactions Tl…O, Tl…S, and Au…S in the Supramolecular Self-Organization, 13C MAS NMR, and Thermal Behavior
- 2017
-
In: Russian journal of coordination chemistry. - : Maik Nauka Publishing. - 1070-3284 .- 1608-3318. ; 43:10, s. 638-651
-
Journal article (peer-reviewed)abstract
- Crystalline polymeric thallium(I) morpholinedithiocarbamate [Tl2{S2CN(CH2)4O}2]n (I) and the heteronuclear ion–polymeric gold(III)–thalium(III) complex ([Au{S2CN(CH2)4O}2][TlCl4])n (II) are preparatively isolated and characterized by X-ray diffraction analysis and 13C MAS NMR spectroscopy. According to the X-ray diffraction data, the main structural units of compounds I and II (CIF files CCDC 1548079 and 1548080) are presented by the binuclear centrosymmetric molecule [Tl2{S2CN(CH2)4O}2], noncentrosymmetric complex cation [Au{S2CN(CH2)4O{2]+, and isomeric complex anions [TlCl4]–. The formation of the three-dimensional polymeric structure (coordination number of Tl is 7), which is not characteristic of thallium(I) dithiocarbamates, is a consequence of the participation of the secondary Tl…O and Tl…S bonds of two types in the supramolecular self-organization of compound I. Nonequivalent secondary interactions of the first type join the binuclear molecules [Tl2{S2CN(CH2)4O}2] into polymer layers, which, in turn, form the three-dimensional polymeric framework due to the secondary bonds Tl…S. The revealed ability of freshly precipitated compound I to the chemisorption of gold(III) from solutions (2 M HCl) makes it possible to obtain heteronuclear supramolecular complex II as an individual form of binding. In the structure of the latter, the pairs of stronger secondary Au…S bonds join the gold(III) cations into dimers [Au2{S2CN(CH2)4O}4]2+ of the angular structure, the structural ordering of which is achieved in the cationcationic polymeric chain ([Au2{S2CN(CH2)4O}4]2+)n of the helical type involving the pairs of less strong Au…S bonds between the adjacent binuclear units. The distorted tetrahedral anions [TlCl4]– are localized between the polymeric chains. The study of the thermal behavior of compounds I and II by simultaneous thermal analysis makes it possible to establish the character of thermal transformations of the substances and to identify Tl2S (I), TlCl, and elemental gold (II) as thermolysis products
|
|
| 2. |
- Gowda, Vasantha, 1986-, et al.
(author)
-
Bi(III) Complexes Containing Dithiocarbamate Ligands: Synthesis, Structure Elucidation by X‐ray Diffraction, Solid‐State 13C/15N NMR, and DFT Calculations
- 2020
-
In: ChemistrySelect. - : John Wiley & Sons. - 2365-6549. ; 5:29, s. 8882-8891
-
Journal article (peer-reviewed)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.
|
|
| 3. |
- Gowda, Vasantha, et al.
(author)
-
DFT calculations in the assignment of solid-state NMR and crystal structure elucidation of a lanthanum(iii) complex with dithiocarbamate and phenanthroline
- 2016
-
In: Dalton Transactions. - : Royal Society of Chemistry (RSC). - 1477-9226 .- 1477-9234. ; 45:48, s. 19473-19484
-
Journal article (peer-reviewed)abstract
- The molecular, crystal, and electronic structures as well as spectroscopic properties of a mononuclear heteroleptic lanthanum(iii) complex with diethyldithiocarbamate and 1,10-phenanthroline ligands (3 : 1) were studied by solid-state 13C and 15N cross-polarisation (CP) magic-angle-spinning (MAS) NMR, X-ray diffraction (XRD), and first principles density functional theory (DFT) calculations. A substantially different powder XRD pattern and 13C and 15N CP-MAS NMR spectra indicated that the title compound is not isostructural to the previously reported analogous rare earth complexes with the space group P21/n. Both 13C and 15N CP-MAS NMR revealed the presence of six structurally different dithiocarbamate groups in the asymmetric unit cell, implying a non-centrosymmetric packing arrangement of molecules. This was supported by single-crystal X-ray crystallography showing that the title compound crystallised in the triclinic space group P1[combining macron]. In addition, the crystal structure also revealed that one of the dithiocarbamate ligands has a conformational disorder. NMR chemical shift calculations employing the periodic gauge including projector augmented wave (GIPAW) approach supported the assignment of the experimental 13C and 15N NMR spectra. However, the best correspondences were obtained with the structure where the atomic positions in the X-ray unit cell were optimised at the DFT level. The roles of the scalar and spin-orbit relativistic effects on NMR shielding were investigated using the zeroth-order regular approximation (ZORA) method with the outcome that already the scalar relativistic level qualitatively reproduces the experimental chemical shifts. The electronic properties of the complex were evaluated based on the results of the natural bond orbital (NBO) and topology of the electron density analyses. Overall, we apply a multidisciplinary approach acquiring comprehensive information about the solid-state structure and the metal-ligand bonding of the heteroleptic lanthanum complex.
|
|
| 4. |
- Gowda, Vasantha, et al.
(author)
-
Modelling and structrual optimizations of rare earth coordination : First principles calculations
- 2013
-
Conference paper (other academic/artistic)abstract
- An approximate 3D structure for the yttrium diethyldithiocarbamato-phenanthroline complex 1, obtained by manually replacing the Nd3+ ion with Y3+ion of the reported crystal structure for neodymium diethyldithiocarbamato-phenanthroline complex 2 followed by DFT geometry optimization using periodic boundary conditions with dispersion corrected functional, has been compared with DFT optimized structure for 1. The quality of the method is discussed by comparing predicted PXRD pattern, high resolution solid state 13C and 15N CP/MAS NMR data and calculated chemical shift tensor eigenvalues for optimized structures for 1 and 2. We have observed an excellent agreement between the ‘modeled’ and experimental structures. Finally, to take into account the relativistic effects on NMR shielding calculations, we have employed the zeroth-order regular approximation (ZORA) formalism using Slater-type orbital (STO) basis sets implemented in Amsterdam Density Functional (ADF) package. The present approach can be further extended to study other complexes of rare earth metals in general, particularly those having similar crystal structure.
|
|
| 5. |
- Gowda, Vasantha, et al.
(author)
-
Structural characterisation of amyloid-like fibrils formed by an amyloidogenic peptide segment of β-lactoglobulin
- 2021
-
In: RSC Advances. - : Royal Society of Chemistry. - 2046-2069. ; 11:45, s. 27868-27879
-
Journal article (peer-reviewed)abstract
- 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 β-lactoglobulin (β-LG11–20), 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 13C and 15N resonances in the solid-state NMR spectra for the β-LG11–20 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 β-LG11–20 fibrils were probed using NMR experiments of the peptide with 13C- and 15N-labelled amino acid residues at selected positions. We can conclude that the peptides form parallel β-sheets, but the NMR data was inconclusive regarding inter-sheet packing. Molecular dynamics simulations confirm the stability of parallel β-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.
|
|
| 6. |
- Gowda, Vasantha, et al.
(author)
-
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
- 2017
-
In: Polyhedron. - : Elsevier. - 0277-5387 .- 1873-3719. ; 129, s. 123-132
-
Journal article (peer-reviewed)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 () 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.
|
|
| 7. |
- Gowda, Vasantha, et al.
(author)
-
Structural investigations of rare earth dialkyl dithiocarbamate complexes: solid-state NMR, X-ray diffraction and DFT calculation studies
- 2013
-
Conference paper (other academic/artistic)abstract
- 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.
|
|
| 8. |
- Gowda, Vasantha, et al.
(author)
-
Structure Elucidation of an Yttrium Diethyldithiocarbamato-Phenanthroline Complex by X-ray Crystallography, Solid-State NMR, and ab-initio Quantum Chemical Calculations
- 2016
-
In: European Journal of Inorganic Chemistry. - : Wiley. - 1434-1948 .- 1099-1948 .- 1099-0682. ; 20, s. 3278-3291
-
Journal article (peer-reviewed)abstract
- We present a structural analysis method for molecular and electronic structure of yttrium diethyldithiocarbamato-phenanthroline complex {[Y(S2CNR2)3PHEN] with R = C2H5 and PHEN = 1,10-phenanthroline} combining solid-state NMR spectroscopy, XRD, and first principles DFT calculations. Replacing the Nd3+ ion with Y3+ in the reported crystal structure of [Nd(S2CNR2)3PHEN] complex generated an approximate 3D structure of the title complex. The structure was then subjected to first principles quantum chemical geometry optimisation using periodic DFT method. The quality of the method is discussed by comparing predicted and experimental powder XRD patterns. Full assignment of 13C and 15N solid-state CP-MAS NMR spectra as well as analyses of the principal values of the chemical shift tensors were carried out using periodic scalar relativistic DFT modelling. Spin-orbit relativistic effects, estimated by SO-ZORA formalism for one molecular unit, were evaluated. Finally, the X-ray structure of the title complex was determined, which proved that the former procedure is appropriate. The most important orbital interactions were investigated by Natural Bond Orbital analysis. The isotropic shielding values for S2CN-carbons were analysed by Natural Localised Molecular Orbital analysis. The present approach can be further extended to study other rare earth metal complexes, particularly those having similar but not yet solved crystal structures
|
|
| 9. |
- Ivanov, Alexander V., et al.
(author)
-
Chemisorption Synthesis of the Ion-Polymeric Heteronuclear Gold(III)-Bismuth(III) Complex ([Au{S2CN(C3H7)2}2]3[Bi2Cl9])n Based on [Bi2{S2CN(C3H7)2}6]: 13C MAS NMR, Supramolecular Structure, and Thermal Behavior
- 2018
-
In: Russian journal of coordination chemistry. - : Springer. - 1070-3284 .- 1608-3318. ; 44:8, s. 518-531
-
Journal article (peer-reviewed)abstract
- Chemisorption synthesis on the basis of the binuclear compound [Bi2{S2CN(C3H7)2}6] (I) and preparative isolation of the ion-polymeric heteronuclear gold(III)-bismuth(III) complex ([Au{S2CN(C3H7)2}2]3[Bi2Cl9])n (II) are carried out. Compounds I and II are characterized in comparison by IR spectroscopy and 13C CP-MAS NMR. According to the X-ray diffraction analysis data (CIF file CCDC no. 1407705), the cationic moiety of compound II exhibits an unusually complicated supramolecular structure including six isomeric noncentrosymmetric complex cations [Au{S2CN(C3H7)2}2]+ (hereinafter A-F) and two binuclear anions [Bi2Cl9]3- as conformers. The isomeric gold(III) cations perform various structural functions. Owing to pair secondary interactions Au···S, cations B, C, E, and F form centrosymmetric ([E···E], [F···F]) and noncentrosymmetric ([B···C]) binuclear aggregates [Au2{S2CN(C3H7)2}4]2+, whereas cations A and D are not involved in dimerization. The strongest secondary Au···S bonds are formed between the binuclear and mononuclear cations, resulting in the formation of supramolecular cation-cationic polymer chains of two types: (⋅⋅⋅A⋅⋅⋅[B⋅⋅⋅C]⋅⋅⋅A⋅⋅⋅[B⋅⋅⋅C]⋅⋅⋅)n and (D⋅⋅⋅[E⋅⋅⋅E]⋅⋅⋅D⋅⋅⋅[F⋅⋅⋅F]⋅⋅⋅])n. In both chains, the gold atoms of the binuclear cations are characterized by a distorted octahedral coordination [S6], whereas in the mononuclear cations the gold atoms retain the square environment [S4]. The cation-anionic interactions are provided by secondary bonds Cl⋅⋅⋅S involving the terminal chlorine atoms of isomeric [Bi2Cl9]3- and the sulfur atoms of the binuclear cations [Au2{S2CN(C3H7)2}4]2+. The character of the thermal behavior of compounds I and II is studied by simultaneous thermal analysis with the identification of intermediate and final products of the thermal transformations. The thermolysis of compound I at 193-320°C is accompanied by the formation of Bi2S3 with an impurity of reduced metallic bismuth particles. The final products of the thermal transformations of compound II are reduced elemental gold and Bi2O3, and the thermal transformation intermediates are BiCl3 and Bi2S3.
|
|
| 10. |
- Gowda, Vasantha, 1986-
(author)
-
Experimental and Computational Magnetic Resonance Studies of Selected Rare Earth and Bismuth Complexes
- 2017
-
Doctoral thesis (other academic/artistic)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 initioquantum 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 aunique NMR fingerprint of the metal centre both in liquid and solid phase. The solid-state 13C and 15NNMR 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.
|
|
