A study of lanthanide complexes with di-2-pyridyl ligands
- Authors: Coetzee, Louis-Charl Cloete
- Date: 2016
- Subjects: Rare earth metals
- Language: English
- Type: Thesis , Masters , MTech
- Identifier: http://hdl.handle.net/10948/4731 , vital:20659
- Description: The ligands di(2-pyridyl) ketone (DPK) and cis-1,2 di(2-pyridyl) ethylene (DPE) are N,N,Odonor ligands that can undergo nucleophilic addition and become more flexible for coordination. The reaction between the lanthanide thiocyanate salt and DPK gave rise to seven novel complexes of the general formula [Ln(NCS)3(DPKOH)3], where Ln = La, Ce, Nd, Eu, Tb, Dy and Ho. 1H NMR spectroscopy verified that the ligand underwent nucleophilic addition upon coordination. This was further confirmed using UV-Vis spectroscopy which showed a shift in the absorption bands due to conjugation of electrons within the pyridyl ring upon coordination. UV-Vis spectroscopy was also utilised to test the covalent character of the neodymium and holmium complexes. X-ray diffraction and IR spectroscopy showed that three DPK ligands coordinated bidentately through a pyridinic nitrogen and a hydroxyl oxygen, while three isothiocyanato molecules completed the coordination environment around each metal. Furthermore, X-ray diffraction also revealed that these complexes are isostructural, ninecoordinate and the polyhedron which encloses each ion is of trigonal tricapped prismatic shape with D3h symmetry. Micro-analysis on all the complexes, except lanthanum and holmium confirmed the molecular formulae produced from the crystallographic data of each complex. The reaction between the lanthanide thiocyanate salt and DPE produced poor quality crystals which could not be detected by X-ray diffraction. The lanthanide salts used for this reaction were lanthanum, neodymium, europium, dysprosium and holmium. Upon coordination, conductivity measurements detected the presence of lanthanide ions in each solution. 1H NMR and IR spectroscopic studies showed that the ethylenic moiety of DPE underwent nucleophilic addition upon coordination. UV-Vis spectroscopy further confirmed nucleophilic addition upon coordination due to shifts in absorption bands. IR spectroscopy verified the possibility of a bidentate coordination to each metal through a pyridinic nitrogen and a hydroxyl oxygen as well as a monodentate coordination through isothiocyanato ligands. A micro-analysis on all the complexes provided the molecular formulae that can best fit each complex. The effect of the solvent molecules on the bonding parameters of the lanthanum complex was investigated. An analysis of the results produced from crystallographic data revealed the presence of intermolecular forces which interacted and stabilised the complex.
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- Date Issued: 2016
Synthesis and characterisation of lanthanide complexes with nitrogen- and oxygen-donor ligands
- Authors: Madanhire, Tatenda
- Date: 2016
- Subjects: Rare earth metals
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/13127 , vital:27154
- Description: The reactions of Ln(NO3)3∙6H2O (Ln = Pr, Nd or Er) with the potentially tridentate O,N,O chelating ligand 2,6-pyridinedimethanol (H2pydm) were investigated, and complexes with the formula, [Ln(H2pydm)2(NO3)2](NO3) (Ln = Pr or Nd) and [Er(H2pydm)3](NO3)3 were isolated. The ten-coordinate Pr(III) and Nd(III) compounds crystallise in the triclinic space group P-1 while the nine-coordinate Er(III) complex crystallises in the monoclinic system (P21/n). The reaction of PrCl3∙6H2O with H2pydm yielded the compound, [Pr(H2pydm)3](Cl)3, that crystallises in the monoclinic system, space group P21/c with α = 90, β = 98.680(1) and γ = 90°. The nine-coordinate Pr(III) ion is bound to three H2pydm ligands, with bond distances Pr-O 2.455(2)-2.478(2) Å and Pr-N 2.6355(19)-2.64(2) Å. X-ray crystal structures of all the H2pydm complexes reveal that the ligand coordinates tridentately, via the pyridyl nitrogen atom and the two hydroxyl oxygen atoms. The electronic absorption spectra of complexes show 4f-4f transitions. Rare-earth complexes, [Ln(H2L1)2(NO3)3] [Ln = Gd, Ho or Nd], were also prepared from a Schiff base. The X-ray single-crystal diffraction studies and SHAPE analyses of the Gd(III) and Ho(III) complexes shows that the complexes are ten-coordinate and exhibit distorted tetradecahedron geometries. With proton migration occurring from the phenol group to the imine function, complexation of the lanthanides to the ligand gives the ligand a zwitterionic phenoxo-iminium form. A phenolate oxygen-bridged dinuclear complex, [Ce2(H2L1)(ovan)3(NO3)3], has been obtained by reacting Ce(NO3)3∙6H2O with an o-vanillin derived Schiff base ligand, 2-((E)-(1-hydroxy-2-methylpropan-2-ylimino)methyl)-6-methoxyphenol (H2L1). Hydrolysis of the Schiff base occurred to yield o-vanillin, which bridged two cerium atoms with the Ce∙∙∙Ce distance equal to 3.823 Å. The Ce(III) ions are both tencoordinate, but have different coordination environments, showing tetradecahedron and staggered dodecahedron geometries, respectively. The reaction of salicylaldehyde-N(4)-diethylthiosemicarbazone (H2L2) in the presence of hydrated Ln(III) nitrates led to the isolation of two novel compounds: (E)-2[(ortho-hydroxy)benzylidene]-2-(thiomethyl)-thionohydrazide (1) and bis[2,3-diaza4-(2-hydroxyphenyl)-1-thiomethyl-buta-1,3-diene]disulfide. The latter is a dimer of the former. For this asymmetric Schiff base, 1 and the symmetric disulfide, classical hydrogen bonds of the O–H∙∙∙N as well as N–H∙∙∙S (for 1) type are apparent next to C–H∙∙∙O contacts. 4-(4-Bromophenyl)-1-(propan-2-ylidene)thiosemicarbazide was also prepared upon reacting 4-(4-bromophenyl)-3-thiosemicarbazide with acetone in the presence of ethanol and La(NO3)3∙6H2O. The C=S bond length was found to be 1.6686(16) Å which is in good agreement with other thioketones whose metrical parameters have been deposited with the Cambridge Structural Database. Classical hydrogen bonds of the N–H∙∙∙N and the N–H∙∙∙Br type are observed next to C–H∙∙∙S contacts. All synthesised compounds were characterised by microanalyses, single-crystal X-ray diffraction (except for [Nd(H2L1)2(NO3)3]), 1H NMR and IR spectroscopy.
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- Date Issued: 2016