Transition metal chemistry

1. Transition metal chemistry Coordination compounds – ligands and things Coordinate covalent bonds and ligands Nomenclature Isomerism Spectroscopy Electronic structure

2. Coordinate covalent bond • Lewis acid/base chemistry • Lone pair on water (base) • Vacancy on Fe2+ (acid)

3. Positive, neutral, negative • The complex can be an ion that forms part of a neutral compound - square brackets delineate the complex • Or may exist as a standalone neutral compound (no square brackets)

4. Things to consider • Coordination number – the number of ligands around the central ion • Geometry – the shape of the complex • Much greater variety and complexity compared with the geometry of covalent molecules of the representative elements

5. Examples of complexes with different coordination numbers

6. Geometry - prelude • Rules for determining geometry are more involved than the simple VSEPR approach that works well with covalent compounds • Note: same composition may adopt different geometries • Will be dealt with using ligand-field theory

7. Things to know Overall charge • Writing the correct formula • Determining oxidation state on the central atom • Complex charge - Sum of anion charges = o.s. Square bracket Number of anion ligands Number of neutral ligands

8. Ligands – entities with teeth • Must contain a lone electron pair • Classify the ligands according to the number of available pairs • Monodentate – one pair • Bidentate – two pairs • Polydentate – many pairs

9. Common ligands and names in complex ions

11. Chelating – ligands with claws • Ligands with greater than one lone pair can form more than one bond to a single metal ion • Ethylene diamine (en)– tridentate • EDTA - hexadentate

12. Important biological entities • (a) The structure of the porphine molecule. Loss of the two NH protons gives a planar, tetradentate 2– ligand that can bond to a metal cation. The porphyrins are derivatives of porphine in which the peripheral H atoms are replaced by various substituent groups. (b) Schematic of the planar heme group, the attached protein chain, and the bound O2 molecule in oxyhemoglobin and oxymyoglobin. The Fe(II) ion has a six-coordinate, octahedral environment, and the O2 acts as a monodentate ligand.

13. What’s in a name

14. Rules, rules, rules • If the compound is a salt, naming is as for common salts: cation first and then anion Potassium hexacyanoferrate(III)

15. Complex ion or neutral complex • Ligands first then metal • Endings are the thing • Anionic ligands end in –o • -ide → -o; -ate → -ato • Neutral ligands have normal names except… • H2O (aqua), NH3 (ammine), CO (carbonyl) • One word: nospacebetweenligandandmetal Diamminedichloroplatinum(II)

16. More than one ligand • Indicate number of ligands by prefixes: di-, tri-, etc. • Ligands are listed in alphabetical order Tetraaquadichlorochromium(III) chloride

17. It’s all Greek to me • If the ligand name contains a Greek prefix (ethylenediamine), the ligand name is in parantheses and use an alternative prefix: bis-(2), tris-(3), tetrakis(4) Tris(ethylenediamine)cobalt(III) chloride

18. Roman numerals • Roman numeral in parantheses to indicate oxidation state of metal in situation where the o.s. is variable

19. -ate crimes • -ate is the conventional ending for the metal in an anionic complex • Check table for exact wording