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  4. Bond Characterization and Electronic Configuration of Ti, Mn and Fe Complexes
 
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Bond Characterization and Electronic Configuration of Ti, Mn and Fe Complexes

Date Issued
2006
Date
2006
Author(s)
Lin, Yen-Chen
DOI
en-US
URI
http://ntur.lib.ntu.edu.tw//handle/246246/51643
Abstract
Specific features of electronic configurations of 3d transition metals in complexes and the corresponding interesting behaviors such as bonding characteristics and magnetic properties are pursued. In the first part of this dissertation three transition metal complexes, 1, (NH4)n[Ti(μ2-C2O4)2]n·2nH2O, 2, [Mn(μ3-mal)(H2O)2]n and 3, [Mn3(μ2-mal)2(mal)2(H2O)8]·2H2O, are investigated, of which electron density distributions are extracted from the corresponding high-resolution single crystal X-ray diffraction data by applying the aspherical multipole model refinement. The five 3d orbital populations of the metal sites (Ti in 1 and Mn in 2 and 3) derived from multipole terms are found to be well suited with the local coordination spheres. The total numbers of 3d electrons are also comparable with the corresponding net atom in molecule (AIM) charges. Significant difference between the two Mn atoms in 3 (which are expected to be MnIII and MnII, respectively) is not found though slight difference is still observable. M-O bonds in all the three complexes (M = Ti in 1 and Mn in 2 and 3) exhibit a total different bonding characteristic in comparison with those of organic fragments e.g. C-C, C-O and O-H, among which those with positive total energetic densities are characterized as close-shell interactions while those with negative total energetic densities are characterized as transit closed-shell interactions. The correlations between topological properties and the accompanied energetic densities of metal-oxygen bonds are inspected; the result shows similar behaviors with those of hydrogen bonding interactions. In the second part of the thesis, three spin crossover (SCO) systems (4, [Fe(μ2-btr)2(NCS)2]·H2O, 5, [Fe0.7Co0.3(μ2-btr)2(NCS)2]·H2O and 6, [Fe(μ2-btr)3](ClO4)2) are studied, of which transitions between spin states of metal sites are observed as the consequence of external perturbations. X-ray absorption spectroscopy at both metal K-edge and L-edge is performed to probe directly the exact electronic configurations of target metal centers. Typical spectra of FeII at HS and LS states are reproduced adequately. Spectrum measured after irradiation with a 532 nm laser source at 27 K is comparable with that at RT, revealing that the light-induced excited spin state trapping (LIESST) state exhibit a HS configuration. Spin state conversions with increasing temperature are monitored as well by a series of absorption spectra (at K-edge for 4 and L-edge for 6) where unexpected smoothened evolutions originated from sample grinding are obtained. For 4, the loss of SCO phenomenon after dehydration is pursued as well by synchrotron powder X-ray diffraction. A reversible structure phase transition from monoclinic C 2/c to triclinic P is evidenced. The anhydrous species yields a contracted unit cell especially in the direction along the normal of the 2D layer. The distance between adjacent layers is significantly shortened from 5.56 Å to 4.63 Å together with a slight sliding parallel to the layer. Consequently, the compressed free space may restrict the necessary structure fine-tuning accompanied with the change in spin state and thus limit the occurrence of spin transition.
Subjects
電子密度分佈
磁自旋交換
粉末X光繞射
X光吸收光譜
electron density distribution
spin crossover
powder XRD
XAS
Type
thesis
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