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Chapter 24: Transition Metals Coordination Compounds Part 2 Transition Metals • The transition metals include the d-block, Groups 3-12. • The inner transition metals include the f-block elements. • Many transition metals form beautifully colored solids and solutions. • Why are so many transition metal complexes colored? • Usually only metals with d0 or d10 form colorless compounds (Zn, Ag). • Colors in metal complexes (or any compound) is due to their absorption spectrum. • When a metal complex absorbs light, an electron undergoes an electronic transition from a ground state to an excited state. • Remember: E = hc/ OR = hc/ E • We see the color which is NOT absorbed, but which was reflected or transmitted. • We see the complementary color of what was absorbed. Crystal Field Theory • Why do metal complexes absorb light in the Vis light spectrum? • Crystal Field Theory tries to explain this. • When a ligand approaches a free metal atom or ion in order to form a bond, e-e repulsions occur between the metal’s d-electrons and the ligands electrons. • This causes the metal’s 5 degenerate d-orbitals to increase in energy AND to split. • So they are no longer degenerate. • Different ligands cause more of an energy split in the d-orbitals. • Ligands which cause the d-orbitals to split more with a higher E are called strong-field ligands. • Ligands which cause the d-orbitals to split less with a lower E are called weak-field ligands. • Ligand Series from Weak to Strong: I-<Br-<Cl-<F-<H2 O<NH3<en<CN- • Ligand splitting of a metal’s d-orbitals also explains why some complexes are highly paramagnetic and others are diamagnetic or weakly paramagnetic. • Highly Paramagnetic: These are weak field complexes with a low E, so the d-e are easily promoted. The result is a complex with many unpaired electrons, or a high-spin complex. Octahedral Complexes Tetrahedral & Square Planar Complexes