Spinel Structures. CFT aids in understanding the arrangements of metal ions in spinel structures (R.C. Chpt.12). READ R.C. WHERE SPINEL STRUCTURES ARE OUTLINED IN DETAIL. (p ). The spinel is a MIXED METAL OXIDE with a general formula (M 2+ )(2M 3+ )(O 2- ) 4.. Spinel is MgAl 2 O 4 Many compounds adopt this type of structure. The basic structure is a FCC lattice of O 2- anions. Cations occupy tetrahedral and octahedral holes. How does CFT help us understand this structure?

Spinel structures and CFT Normal Spinal Structure. M 2+ is tetrahedral, M 3+ is octahedral Example: (Mg 2+ ) T (2Al 3+ ) O (O 2- ) 4 Inverse Spinal Structure. M 2+ is octahedral M 3+ is tetrahedral and in the remaining octahedral holes Example: (Fe 3+ ) T (Fe 2+,Fe 3+ ) O (O 2- ) 4 This later example is magnetite or Fe 3 O 4. Fe 3 O 4 (Fe 2+, 2Fe 3+, 2O 2- ) Note the O 2- is a weak field ligand. (Fe is H.S.) What are the electron configurations of the Fe ions? Fe 0 is d 8 egeg t 2g oo 3/5  o 2/5  o d xy, d yz, d xz d x2-y2, d z2 OR Fe 2+ egeg TT 3/5  T 2/5  T d xy, d yz, d xz d x2-y2, d z2

Mn 3 O 4 Spinel Structure. Mn 3 O 4 (Mn 2+, 2Mn 3+, 4O 2- ) Electron configurations are ….. ? egeg t 2g oo 3/5  o 2/5  o d xy, d yz, d xz d x2-y2, d z2 OR egeg TT 3/5  T 2/5  T d xy, d yz, d xz d x2-y2, d z2

How does CFT measure up? I. Colours of Transition Metal Complexes Why are most transition metal complexes brightly coloured but some aren't? Why do the colours change as the ligand changes? Why do the colours change as the oxidation state of the metal changes, even for complexes of the same ligand? II. Why do different complexes of the same metal ion in the same oxidation state have different numbers of unpaired electrons? Why are there only certain values of the number of unpaired electrons for a given metal ion? III. Why do some transition metal ions seem to have a fixed coordination number and geometry, while other metal ions seem variable? IV. Why do some metal complexes undergo ligand-exchange reactions very rapidly and other similar complexes react very slowly, yet this reaction is thermodynamically favorable?

Course Outline I.Introduction to Transition Metal Complexes. Classical complexes (Jorgenson and Werner) Survey of ligand coordination numbers, geometries and types of ligands Nomenclature Isomerism II.Bonding in Transition Metal Complexes. Electron configuration of transition metals Crystal field theory Valence bond theory Simple Molecular Orbital Theory Electronic Spectra and Magnetism III.Kinetics and Mechanisms of Inorganic Reactions. Stability and lability Substitution reactions Electron transfer reactions IV.Descriptive Chemistry of TMs. V.Organometallic Chemistry 18 e - rule, , and  bonding ligands (synergistic bonding) Metal carbonyls, synthesis, structure, reactions Compounds with delocalized  -conjugated organic ligands. Reactions and catalysis