Transition Metals and Coordination Compounds

Transition Metals The transition metals are the d-block elements. The Inner Transitions metals are the lanthanides and actinides, or the f-block. Many transition metals form highly colored compounds. Many are critical for our health!

d-block & Valence Electrons How many valence electrons does iron have? How many valence electrons does gold have? For the d-block, there are (n-1)d + ns valence electrons. Why do we count the d electrons???

d-block & Valence Electrons How about ions? How many valence electrons does Cu have and how many does Cu +1 have? What are their electron configurations?

Oxidation States Many transition metals are found in more than 1 oxidation states, even Ag and Zn! Here are some common states:

Oxidation States We can assign oxidation states using the rules you already learned to love! Determine the oxidation states for the transition metals in the following complexes:

Coordination Compounds The preceding complexes are examples of coordination compounds or coordination complexes. Note that they may be neutral or charged. What do you notice? What do you think is the central atom?

Coordination Compounds In coordination compounds, the central atom is a metal atom or ion, and it is covalently attached to 2 or more molecules or ions. The molecules or ions covalently attached to the transition metal are called ligands.

Coordination Compounds In a ligand, the atom(s) which are directly attached to the metal are called the ligand donor atoms or simply the donor atoms. Look at the following and determine what the ligands are, and what the donor atoms are.

Complex Ions If the coordination compound has a charge, it is a complex ion. We write it in brackets with the charge outside. But if it ’ s an ion, what can it do? Complex ions can form ionic salts. How do we write the formulas for these complex salts?

Coordination Numbers We also talk about coordination numbers for coordination compounds. The coordination number for a transition metal is the number of ligand donor atoms directly attached to it.

Coordination Numbers Common coordination numbers are 2, 4, or 6, but they may be anything from 2 to 8 (including odd).

Coordination Numbers What is the coordination number for the following:

Common Ligands Ligands may actually form more than 1 bond or attachment to the transition metal. Ligands which form only 1 bond are called monodentate ligands. Ligands which form more than 1 bond are called polydentate ligands. Bidentate ligands are fairly common.

Common Ligands Let ’ s look at some polydentate ligands and how they bond or attach.

Common Ligands You do need to know the most common ligands so you can name transition compounds. The following table has all that you need to know except the pyridine ligand which is abbreviated py.

Structure Before we switch to nomenclature, what about the structures? As the most common coordination numbers are 2, 4, and 6, there are 4 common geometric shapes: –linear –tetrahedral –square planar –octahedral

Structure What ’ s the transition metal hybridization associated with these shapes?

Nomenclature There are some rules to name the simpler coordination compounds. 1.If the complex is a salt, name the cation portion first, then name the anion.

Nomenclature 2.When naming a complex ion or a neutral complex, name the ligands using the appropriate prefix (di, tri, tetra, etc), then name the metal. If a ligand is an anion, it name ends in -o (like chloro or cyano). Specify the metal oxidation # with a Roman numeral inside ( ). If there are more than 1 different ligands, name them alphabetically, ignoring the prefixes.

Nomenclature 3.If the ligand atom itself contains a prefix (for you this is ethylenediamine), then put the name inside ( ), and use one of the following prefixes to specify the number of these ligands: 2 is bis, 3 is tris, 4 is tetrakis. 4.If the complex ion is an anion, give the metal an -ate ending.

Isomers Isomers are compounds with the same molecular formula but have the atoms arranged differently. There are several types of isomers: –Conformational or Structural –Geometric or Diasteorisomers –Enantiomers

Transition Metals and Color Why are so many transition metal complexes colored? Usually only metals with d 0 or d 10 form colorless compounds (Zn, Ag). Colors in metal complexes (or any compound) is due to their absorption spectrum.

Transition Metals and Color 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.

Colors of Visible Light

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.

d-Orbital Splitting by Ligands

Octahedral Complexes and Orbitals

Crystal Field Theory 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 - <H 2 O<NH 3 <en<CN -

Octahedral Complexes: Weak Field / Strong Field Ligands

Crystal Field Theory 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.

Tetrahedral & Square Planar Complexes