Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Crystal Field Theory I Crystal field theory:In Crystal field theory, a ligand lone pair is moldeled as a point charge that repels electrons of the d orbitals of the central metal ion. This approach concentrates on the resulting splitting of the d orbitals into groups of different energies. Octahedral complexes: in an octahedral ligand field the d-orbitals split in two energy levels. Two of the orbitals, namely dz2 and dx2-y2 (eg-orbitals) point directly towards the ligands, and three orbitals, namely dxy dxz and dyz (t2g-orbitals) point between the ligands. The first ones have a greater electrostatic repulsion by the negative charges of the ligands, the latter three d- orbitals have a lower electrostatic repulsion. Ligand field splitting parameters: The difference in energy between the eg orbitals and the t2g orbitals is called Δo (o for octrahedral). For octahedral complexes with the electronic configurations d4, d5, d6 and d7 exist two possibilities to fill the orbitals with electrons, depending on the value of Δo in comparison to the value of the spin pairing energy. In complexes with strong ligands, which cause a large Δo, first the lower energy orbitals are completely filled. The result for the mentioned electronic configurations are so called “low spin complex”. In complexes with weak ligands, the eg and t2g orbitals are filled according Hund’s rule. The result for the mentioned electronic configurations are so called “high spin complex” (Hund’s rule: when more than one orbital has the same energy, electrons occupy first separate orbitals with parallel spins.↑↑) The Spectrochemical Series: weak ligands: I-<Br-<S2-<SCN-<Cl-<NO3-<N3-<F-<OH-<C2O42-<H2O<NCS-<CH3CN<py<NH3<en<2,2'-bipyridine<phen<NO2-<PPh3<CN-<CO strong ligands central atom: Δo increases down a group and increases with increasing oxidation number Color of transition metal complex: The transition metal complex can absorb the energy of the visible light, this energy of the visible light is used to excite from the lower energy orbital to the higher energy orbital. Because only certain wavelengths (λ) of light are absorbed - those matching exactly the energy difference - the compounds appears colored (complementary color!!). Literature Shriver, D. F., Atkins, P. W., Lanford, C. H., Inorganic Chemistry (2006), fourth edition Questions: 1) Please sketch the splitting of the d-electron levels in octahedral complex according to the crystal field theory and explain the figure. 2) Which of the following complexes is a low spin complex: [Fe(H2O)6]3+ or Fe(CN)6]3-. Explain why.