PHD
  1. Inorganic chemistry  1.1. Coordination chemistry  1.1.1. Ligand field theory  1.1.2. Crystal field theory  1.1.3. Molecular Orbital Theory for Coordination Compounds  1.1.4. Stability of Coordination Compounds  1.1.5. Electronic spectra of coordination compounds  1.1.6. Isomerism in Coordination Compounds  1.1.7. Kinetics and mechanism of coordination reactions  1.2. Organometallic Chemistry  1.2.1. Metal Carbonyls  1.2.2. Metal alkyl and aryl  1.2.3. Fischer and Schrock carbonaceans  1.2.4. Oxidative Addition and Reductive Elimination  1.2.5. Metal Hydrides  1.2.6. Catalysis by organometallic compounds  1.2.7. Metallocenes and Sandwich Complexes  1.2.8. CH activation  1.3. Solid state chemistry  1.3.1. Crystal structures and lattices  1.3.2. Band theory and electrical properties  1.3.3. Defects in the crystal  1.3.4. Synthesis of solid state materials  1.3.5. Magnetic and optical properties of solids  1.3.6. Superconductivity  1.3.7. Solid state ionics  1.4. Bio-inorganic chemistry  1.4.1. Metalloproteins and enzymes  1.4.2. Metal ion transport and storage  1.4.3. The role of metals in medicine  1.4.4. Bioinspired catalysis  1.4.5. Metal–DNA interactions  1.4.6. Metal Complexes in Medical Science  1.5. Lanthanides and Actinides  1.5.1. Electronic configuration and oxidation states in lanthanides and actinides  1.5.2. Spectral and Magnetic Properties in Lanthanides and Actinides  1.5.3. Separation and Extraction of Lanthanides and Actinides  1.5.4. Coordination chemistry of f-block elements  1.6. Main Group Chemistry  1.6.1. Chemistry of boron compounds  1.6.2. Chemistry of Silicon and Germanium Compounds  1.6.3. Chemistry of Phosphorus and Sulfur Compounds  1.6.4. Organosilicon chemistry  1.6.5. Noble Gas Chemistry
  2. Organic chemistry  2.1. Reaction mechanism  2.1.1. Nucleophilic substitution reactions  2.1.2. Electrophilic addition and substitution reactions  2.1.3. Elimination reactions  2.1.4. Rearrangement reactions  2.1.5. Radical reactions  2.1.6. Pericyclic Reactions  2.1.7. Photochemical reactions  2.2. Stereoscopic  2.2.1. Chirality and optical activity  2.2.2. Structural analysis  2.2.3. Stereoelectronic effects  2.2.4. Asymmetric synthesis  2.2.5. Dynamic Stereochemistry  2.3. Organometallic Chemistry in Organic Synthesis  2.3.1. Organolithium and organomagnesium reagents  2.3.2. Transition metal catalyzed coupling reactions  2.3.3. Palladium-catalyzed reactions  2.3.4. Olefin Metathesis  2.3.5. Gold and silver catalysis  2.4. Natural products chemistry  2.4.1. Alkaloids and terpenoids  2.4.2. Steroids and Flavonoids  2.4.3. Total synthesis of natural products  2.4.4. Biosynthesis of natural products  2.5. Supramolecular Chemistry  2.5.1. Host-Guest Chemistry  2.5.2. Self-assembly and molecular recognition  2.5.3. Supramolecular Catalysis  2.5.4. Molecular Machines
  3. Physical Chemistry  3.1. Thermodynamics  3.1.1. Laws of Thermodynamics  3.1.2. Chemical Potential and Equilibrium  3.1.3. Statistical thermodynamics  3.1.4. Non-equilibrium thermodynamics  3.2. Quantum Chemistry  3.2.1. Schrödinger equation and its applications  3.2.2. Molecular orbital theory  3.2.3. Density functional theory  3.2.4. Post-Hartree–Fock methods  3.3. Chemical kinetics  3.3.1. Reaction rate theory  3.3.2. Mechanism and rate laws  3.3.3. Catalysis and enzyme kinetics  3.3.4. Reaction dynamics  3.4. Spectroscopy and molecular structure  3.4.1. Infrared Spectroscopy  3.4.2. UV-visible spectroscopy  3.4.3. Nuclear Magnetic Resonance Spectroscopy  3.4.4. Mass Spectrometry  3.4.5. Raman Spectroscopy  3.5. Surface and Colloid Chemistry  3.5.1. Absorption and Catalysis  3.5.2. Surfactants and micelles  3.5.3. Colloidal Stability  3.5.4. Nanomaterials and Interfaces
  4. Analytical chemistry  4.1. Chromatography  4.1.1. Gas Chromatography  4.1.2. High Performance Liquid Chromatography  4.1.3. Thin Layer Chromatography  4.1.4. Ion Chromatography  4.2. Electroanalytical techniques  4.2.1. Voltammetry and Polarography  4.2.2. Conductometry and potentiometry  4.2.3. Colometry  4.3. Spectroscopic Methods  4.3.1. Atomic absorption spectroscopy  4.3.2. Fluorescence Spectroscopy  4.3.3. X-ray diffraction  4.3.4. Electron paramagnetic resonance spectroscopy  4.4. Chemometrics  4.4.1. Data processing and statistical methods  4.4.2. Multidisciplinary analysis  4.4.3. Machine Learning in Analytical Chemistry
  5. Theoretical and Computational Chemistry  5.1. Molecular dynamics simulation  5.2. Quantum chemistry methods  5.3. Computational drug design  5.4. Machine Learning in Chemistry  5.5. Ab initio molecular dynamics
  6. Biophysics and Medicinal Chemistry  6.1. Drug discovery and design  6.2. Enzyme kinetics and inhibition  6.3. Chemical biology approach  6.4. Protein-ligand interactions  6.5. Bioorthogonal chemistry
  7. Materials chemistry  7.1. Polymer chemistry  7.1.1. Polymerization mechanism  7.1.2. Functional Polymers  7.1.3. Biodegradable Polymer  7.1.4. Conducting and semiconducting polymers  7.2. Nano Chemistry  7.2.1. Nanoparticles and nanostructures  7.2.2. Carbon-based nanomaterials  7.2.3. Quantum dots  7.3. Energy and Environmental Chemistry  7.3.1. Battery and Fuel Cell Chemistry  7.3.2. Green chemistry and sustainable materials  7.3.3. Photocatalysis

PHD → Inorganic chemistry → Coordination chemistry ↓


Molecular Orbital Theory for Coordination Compounds


Molecular orbital theory (MOT) is a way of understanding the electronic structure of molecules. It is particularly useful for coordination compounds, which are complexes formed between metal ions and ligands. In this lengthy explanation, we will look at how MOT applies to coordination compounds, focusing on how molecular orbitals are formed and how they determine the properties and behavior of these compounds.

Understanding molecular orbital theory

Molecular orbital theory holds that atomic orbitals combine to form molecular orbitals, which are spread throughout the molecule. The electrons in these orbitals are delocalized, meaning that they are not confined to the space around a single atom, but belong to the entire molecule.

In a simple molecule such as H 2, the atomic orbitals of the two hydrogen atoms combine to form a pair of molecular orbitals - one bonding and one restricting. The bonding molecular orbital is lower in energy and is where the molecule's electrons prefer to be.

Coordination compounds and ligands

Coordination compounds contain a central metal atom or ion surrounded by molecules or ions called ligands. Ligands are electron pair donors and coordinate with the metal, forming complexes such as [Fe(CN) 6 ] 4− or [Cu(NH 3 ) 4 ] 2+.

Molecular orbital theory can explain bonding in these complexes by considering the interactions between the atomic orbitals of the metal and the orbitals of the ligand. Infinite combinations of these atomic orbitals form innumerable molecular orbitals.

Visual example of orbital interactions:

d xy P x P Y MO

In this example, d xy, p x, and p y orbitals of a metal interact with ligands to form a collective molecular orbital (MO).

Construction of molecular orbitals in coordination compounds

In coordination compounds, the metal-ligand interaction is central to the formation of molecular orbitals. Typically, this process can be thought of in steps:

1. Atomic orbitals of metal and ligand

The metal at the center of the coordination compound has empty orbitals that can accept electrons. These typically include d, s and p orbitals. When interacting with ligands, these will combine to form molecular orbitals with different energy levels.

2. Combination and overlap with ligand orbitals

The atomic orbitals on the ligand, which are usually lone pair orbitals on atoms such as nitrogen or oxygen, will overlap with the orbitals of the metal center, creating bonding and restricting molecular orbitals.

3. Filling of molecular orbitals

Electrons from the metal and ligand fill these newly created molecular orbitals, starting from the lowest energy level, just as electrons fill atomic orbitals. The filling of these molecular orbitals determines the electronic configuration of the complex.

Example: octahedral coordination complex

Consider an octahedral complex, one of the most common types of coordination compounds. In an octahedral complex, the metal is surrounded by six ligands arranged at the corners of an octahedron.

The bonding in such a complex can be characterized by looking at the interaction of the metal's d orbitals with the ligand orbitals.

d-orbitals d xy d) d xz x² - y² d z² Molecular orbitals σ* σ π* π δ

Looking at the above example, we see that d z² and d x²-y² orbitals of the metal will form sigma bonds with the ligand orbitals because they have a perpendicular orientation with the axis connecting the metal to the ligands. Other d orbitals such as d xy, d yz, and d xz will form pi bonds.

The energy level diagram shows how molecular orbitals form with different energy levels, represented by σ, π, and δ.

Modifications of energy levels: crystal field theory

While molecular orbital theory explains bonding interactions in a qualitative sense, crystal field theory (CFT) provides a more detailed picture of the electronic distribution by taking into account the effects of the ligand's electric field on the metal's d orbitals. Although it is a semi-quantitative theory, CFT still influences the understanding within the realm of molecular orbital theory.

CFT introduces the idea of d-orbital splitting, where the distortion of d orbitals in the free ion is removed by the presence of coordinating ligands.

Example: Energy level splitting in an octahedral complex

Free ions Ligand field splitting T2G e.g. ΔO

The energy level diagram splits d orbitals in an octahedral field into t 2g and e g orbitals, with the splitting in energy represented by Δ o. This is an important factor in determining the colour and magnetism of coordination compounds.

Ligand field theory

Ligand field theory (LFT) is a more advanced application combining principles of both molecular orbital theory and crystal field theory. It considers the effect of the ligand's orbitals in bonding and is particularly useful for understanding electronic transitions.

In the context of molecular orbital theory, LFT refines the understanding of how ligands contribute electron density to the d-orbitals of metals, and affect properties such as electronic spectra and magnetic properties.

Hybridization concept

When talking about coordination complexes, another level to consider is hybridization. Hybridization provides a model for understanding the geometry and bond angles in complexes:

S P x P Y P Z

Illustration of sp 3 hybridisation, where one s and three p orbitals combine, which affects the geometry of the complex and explains its tetrahedral shape.

Factors affecting molecular orbital formation in complexes

Several factors influence the formation and distribution of molecular orbitals in coordination compounds:

  • Nature of Metal: The atomic orbitals available on the metal and their relative energies are important in determining the molecular orbital structure. Transition metals, because of their d orbitals, exhibit more complex MO interactions than the main group metals.
  • Types of Ligands: Ligands can be classified based on the strength of their field (for example, strong-field ligands such as CN - result in large splitting energies).
  • Geometry: The spatial arrangement determines how the orbitals overlap and hybridize, which in turn affects the molecular orbital diagram.

Conclusion

Understanding molecular orbital theory in coordination compounds provides insight into their chemistry and properties. It provides a detailed picture of how the complex interactions between metals and ligands determine the electronic structure. By combining this understanding with experimental data and complementary theories such as crystal field and ligand field theory, chemists can predict the physical and chemical behavior, thereby aiding in the design and use of such compounds in a variety of applications.


PHD → 1.1.3


U
username
0%
completed in PHD

← Prev (1.1.2)
Crystal field theory
Next (1.1.4) →
Stability of Coordination Compounds

Comments 



Molecular Orbital Theory for Coordination Compounds

https://www.chemistryelite.com/phd/1.1.3?ceal=en