Synthesis and characterisation of lanthanide complexes with potential nitrogen- and oxygen-donor schiff base ligands
- Authors: Pikoli, Sibongile
- Date: 2020
- Subjects: Rare earths , Schiff bases
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/47050 , vital:39778
- Description: This research describes the coordination chemistry of lanthanide complexes with potentially multidentate nitrogen- and oxygen-donor Schiff base derivatives. The studies were performed using various physico-chemical techniques including melting point, IR and NMR spectroscopy, UV-Vis spectroscopy, elemental analyses, conductivity measurements, X-ray crystallography and cyclic voltammetry. The reaction of [Ln(NO3)3·xH2O] (Ln = Nd, Gd, Yb; x = 6 for Nd and Gd, x = 5 for Yb) with the flexible salen-type Schiff base ligand 1,3-bis(o-hydroxybenzylideneamino)propane (H2L1) produced three polynuclear complexes with the general formulae {[Nd(µH2L1)4(NO3)3]·2H2O}n and [Ln(µ-H2L1)2(NO3)6(H2L1)] (Ln = Gd and Yb). Single-crystal Xray crystallography revealed a ten-coordinate polymeric Nd(III) complex that crystallised in the monoclinic space group P21/c, and isostructural nine-coordinate binuclear Gd(III) and Yb(III) complexes (triclinic system, space group P-1). The lanthanide contraction effect is clear across the series. The flexible nature of HL2 results in the self-assembly of the Nd(III) complex in a 1D polymer chain by acting as the bridge between the metal ions. The Nd-Ophenolate bond distances are 2.403(18), 2.463(17), 2.379(17) and 2.367(19) Å and the average Nd-Onitrate bond length is 2.671 Å. Furthermore, the electronic absorption spectra displays 4f→4f transitions solely for the neodymium(III) compound. The syntheses and characterisation of the lanthanide complexes, [La(HL2)3(NO3)3], [Dy(HL2)2(NO3)3] and [Dy(HL2)2Cl3(H2O)]·2CH2Cl2 with the o-vanillin-derived Schiff base ligand 2-methoxy-6-[(E)-(phenylimino)methyl]phenol (HL2) are reported. The nitro-stabilised La(III) and Dy(III) compounds are ten-coordinate with metabidiminished icosahedron and sphenocorona geometries, respectively. Substitution of the nitrate with chloride ions in the starting metal compounds yielded an eight-coordinate Dy(III) complex that adopts the biaugmented trigonal prism geometry. For all three complexes, HL2 exists as a zwitterion that is bound to the metal centre in a mono- and bidentate fashion via the phenolate and methoxy oxygen atoms. The dysprosium(III) chloride complex is stabilised by both intramolecular N−H···O and intermolecular O−H···C1 hydrogen bonds, while the crystal packing of the Ln(III) nitrate complexes is ensured by mainly intramolecular N−H···O hydrogen bonds. Fluorescence studies displayed characteristic Dy(III) f→f transitions (4F9/2 → 6H15/2), which suggest the ligand HL2 is an effective organic antenna to absorb and transfer energy to the dysprosium ion. A series of mononuclear Nd(III) complexes with the Schiff base derivatives 2-methoxy-6-[(E)(phenylimino)methyl]phenol (HL2), 5-methoxy-2-[(E)-(phenylimino)methyl]phenol (HL3) and 2-methoxy-6-{(E)-[(2-methoxyphenyl)imino]methyl}phenol (HL4) yielded structurally diverse complexes defined by the formulae [Nd(HL2)2(NO3)3], [Nd(HL3)3(NO3)3] and [Nd(HL4)2(NO3)3]·CH3OH. Crystallographic analysis shows HL2 and HL4 coordinate bidentately via the phenolate and methoxy oxygen atoms, while HL3 is bound monodentately through the phenolate oxygen atom. Continuous shape measures depict that the decacoordinate complexes with HL2 and HL4 conform to the sphenocorona and tetradecahedron geometries, respectively, whilst the nona-coordinate Nd(III) complex with HL3 exhibits the muffin geometry. The effect of the ligand substituents and their positions (meta versus para) on the absorption and emission intensities of the complexes is demonstrated. Additionally, the electrochemical behaviour of the o-vanillin-derived Schiff base ligands and their complexes was also investigated, and the results illustrate ligand-based reductions and metal-centred redox potentials that are significantly shifted by the ligand substituents.
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- Date Issued: 2020
Synthesis, crystal structures and molecular modelling of rare earth complexes with bis(2-pyridylmethyl)amine and its derivatives : a quantum chemical investigation of ligand conformational space, complex intramolecular rearrangement and stability
- Authors: Matthews, Cameron
- Date: 2020
- Subjects: Rare earths , Complex compounds , Ligands
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10948/46229 , vital:39517
- Description: Limited research has been performed on the coordination behaviour of hybrid aliphatic and heterocyclic polyamines with trivalent rare earth elements. The rare earth coordination properties of several Nalkylated derivatives of the tridentate ligand bis(2-pyridylmethyl)amine (DPA, HL1) backbone - involving the rare earth elements Y, La-Nd, Sm, Eu and Tb-Lu - have been investigated in this study However, the structural and energetic characteristics of DPA coordination with rare earth elements (REE) have not been studied thus far. Potential applications of DPA-based rare earth complexes are primarily dependent on their electronic and magnetic characteristics, which are affected weakly by the coordination environment, where potential applications may include use as Lanthanide Shift Reagents (LSR), Luminescence probes and small-molecule magnets (SMM). A systematic conformational search of DPA was carried out in this study in order to identify the global minimum conformer and for comparison of the free and coordinated geometries, using the M06(D3) functional belonging to the Density Functional Theory (DFT) family of model chemistries. An understanding of the aforementioned would play an important role in analysis of bulk characterization and the prediction of the reactivity of DPA. Final geometries and electronic energies were obtained from the ‘domain based local pair natural orbital’ (DLPNO)-Møller-Plesset and -coupled cluster theoretical methods, as follows: DLPNO-CCSD(T0)/aug-cc-pVQZ//DLPNO-MP2/aug-cc-pVTZ. Fifteen Single-crystal X-ray diffractometer (SC-XRD) crystal structures of mononuclear rare earth chloride coordination complexes with DPA (RE = La-Nd, Sm, Eu, Tb-Lu and Y) were obtained and geometrically analysed in this study. Three isostructural series of constitutional isomers were identified, consisting of one series of nine-coordinate molecule (M1) and two series of eight-coordinate ion pairs (M2 and M3). This conformational diversity is most likely due the flexible nature of the DPA backbone, as well as the additional stability gained from reduced coordination spheres as a function of decreasing rare earth ionic radii across the lanthanide series (Lanthanide contraction). A Quantum Theory of Atoms-in-Molecules (QTAIM) topological analysis was performed in order to identify and characterise potential hydrogen bonding interactions in H-optimised crystal structures. The crystal structures of five dinuclear (RE = Tb-Tm) and two tetranuclear (RE = Yb and Lu) rare earth chloride complexes with DPA have also been structurally analysed. Furthermore, one mononuclear (RE = Dy), two dinuclear complexes (RE = Dy and Lu) with EtDPA, and one mononuclear complex with the DPA-derivative HL4 (RE = Dy) were structurally characterised. A DFT study of the theoretical interconversion of one real- and two hypothetical- mononuclear lanthanum containing isostructural series (cf. aforementioned crystal structures) was undertaken in order to gain a deeper understanding of the processes involved, in terms of the participating minimum energy paths (MEPs), intermediates and transition states – as determined via the Nudged-Elastic Band (NEB) procedure. This hypothesis is supported by the well-known conformational lability of rare earth complexes, due to the weak/minor covalency of their coordination bonds. An attempt was made to determine the respective energies of one real- and two hypothetical diamagnetic or ‘closed-shell’ constitutional isomers containing the rare earth ions La3+(M1), Y3+(M2) and Lu3+ (M3). It was assumed that the most stable isomers have a greater probability of being observed as the asymmetric unit of the complex crystal structure – assuming weak contributions of lattice or intermolecular interactions towards the geometry of the asymmetric unit.
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- Date Issued: 2020
Synthesis, crystal structures and molecular modelling of rare earth complexes with bis(2-pyridylmethyl)amine: aim topological analysis and ligand conformation search
- Authors: Matthews, Cameron
- Date: 2017
- Subjects: Rare earths , Ligands , Complex compounds
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/8230 , vital:26229
- Description: Eight rare earth complexes with bis(2-pyridylmethyl)amine (DPA) were synthesised and recrystallised, under air-sensitive or low moisture conditions. The crystal structures were successfully determined, via SC-XRD, and the asymmetric units of five complexes (1, 3, 5, 6 and 7) were submitted for DFT molecular modelling calculations, which involved geometry optimisation and frequency calculations. The neutral complexes obtained were bis(bis(2-pyridylmethyl)amine)-trichloro-lanthanum(III) [LaCl3(DPA)2] (1), bis(bis(2-pyridylmethyl)amine)-trichloro-cerium(III)) [CeCl3(DPA)2] (2), bis(μ2-chloro)-diaqua-tetrachloro-bis(bis(2-pyridylmethyl)amine)-di-praseodymium(III) [PrCl2(μ-Cl)(DPA)(OH2)]2 (3) and bis(μ2-methoxo)-bis(bis(2-pyridylmethyl)amine)- tetrachloro-di-dysprosium(III) [DyCl2(μ-OCH3)(DPA)]2 (4). The cationic complexes obtained in this study were dichloro-bis(bis(2-pyridylmethyl)amine)- neodymium(III) chloride methanol solvate [NdCl2(DPA)2]Cl·CH3OH (5), dichloro-bis(bis(2- pyridylmethyl)amine)-dysprosium(III) chloride methanol solvate [DyCl2(DPA)2]Cl·CH3OH (6), dichloro-bis(bis(2-pyridylmethyl)amine)-yttrium(III) chloride methanol solvate [YCl2(DPA)2]Cl·CH3OH (7) and dichloro-bis(bis(2-pyridylmethyl)amine)-lutetium(III) chloride methanol solvate [LuCl2(DPA)2]Cl·CH3OH (8). The ‘Quantum theory of atoms in molecules’ approach was used to investigate the electron density topology, primarily in order to investigate the hydrogen and coordination bonds for three of the eight complexes. Two of the neutral complexes contain the ‘early’ rare earth elements lanthanum and praseodymium and one cationic complex contains the ‘late’ lanthanide element dysprosium. Noncovalent interaction analysis was also performed on the aforementioned complexes in order to gain a deeper understanding of the intra-molecular stereo-electronic interactions. Spin density analysis was used to investigate the distribution of unpaired electron density at and around the metal centres of the aforementioned paramagnetic Pr- and Dy-complexes. A ligand conformation search for DPA was undertaken and 32 low energy conformers were identified and their relative energies were determined using two DFT functionals, namely M06 and M06-2X.
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- Date Issued: 2017