Electronic Configuration and Bond Characterization on Ni, Cu and Se Containing Compounds through Charge Density Studies and X-ray Absorption Spectroscopy
Date Issued
2010
Date
2010
Author(s)
Chuang, Yu-Chun
Abstract
A series of metal-sulfur square planar complexes, (PyH)z[M(MNT)2], where M = Ni and Cu, MNT a non-innocent ligand maleonitriledithiolate, [S2C2(CN)2]z-, z=2, 1, are synthesized in order to characterize the site-selected oxidation-reduction properties. Metal K-edge and L-edge X-ray absorption spectroscopy(XAS) are used to deliver the direct evidence for the oxidation state of metal ion. It is clearly demonstrated that redox reaction takes place in the ligand (Ligand-Based) for Ni complexes but in the metal (Metal-Based) for the Cu complexes. In addition, the sulfur K-edge absorption together with the DFT calculation gives a clear picture on the covalency of M-S bond. With the XAS of metal and S, the oxidation reduction site is firmly established for Cu and Ni complexes. The charge density studies from high resolution single crystal X-ray diffraction measurements at 100K are also investigated to aim at the understanding on the nature of the metal-ligand bond in terms of deformation densities and topological properties associated with the bond critical points (BCP). The d-Orbital populations of metal ion derived from multipole model and the monopole charge thus obtained are agreeable with the redox properties established from XAS.
Charge density studies on Se-containing compounds are undertaken: 3,4-trimethylene-6a-selenaselenophthene contains a linear tri-selenium chain in the molecule, which exhibits a three-centered four-electron bond for Se-Se-Se part. A square planar Ni complex bonded with four selenide ligands, Ni[Se2P(O-iPr)2]2 is studied. Ni-Se bonds are characterized together with the short intermolecular Se-Se contact of 3.294 A. Interestingly, there is a Se square network in the crystal through the intra- and inter- molecular Se×××Se contacts. Such contacts are first characterized by topological analysis and Hirshfeld surface mapping.
The magnetic measurements of three-dimensional and two-dimensional atr-based Fe(II) spin crossover (SCO) framework systems (Fe(atr)3(ClO4)2‧2H2O and Fe(atr)(pyz)(NCS)2‧4H2O) are studied in detail in order to solve the puzzle of the stepwise spin transition phenomena. It is found that the stepwise transition is due to the loss of water molecules in the lattice, where the hydrated/dehydrated forms of 2D and 3D systems apparently exhibit quite different transition temperatures. The solvent-dependent spin crossover phenomena in these structures are systematically demonstrated.
Subjects
Charge Density Analysis
X-ray Absorption Spectroscopy
Spin Crossover
Type
thesis
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