Graduate
  1. Physical Chemistry  1.1. Thermodynamics  1.1.1. Laws of Thermodynamics  1.1.2. Enthalpy and heat capacity  1.1.3. Entropy and free energy  1.1.4. Phase Equilibrium  1.1.5. Statistical thermodynamics  1.1.6. Thermodynamic cycle  1.1.7. Fugacity and activity  1.2. Quantum Chemistry  1.2.1. Principles of quantum mechanics  1.2.2. Schrödinger Equation  1.2.3. Particle in a box  1.2.4. Operators and eigenvalues  1.2.5. Atomic orbitals  1.2.6. Molecular orbital theory  1.2.7. Perturbation theory  1.2.8. Valence bond theory  1.2.9. Hybridization and chemical bonding  1.3. Chemical kinetics  1.3.1. Rate laws and reaction mechanisms  1.3.2. Collision theory  1.3.3. Transition state theory  1.3.4. Enzyme Kinetics  1.3.5. Chain Reactions and Polymerization  1.3.6. Photochemical reactions  1.4. Statistical mechanics  1.4.1. Partitioning functions  1.4.2. Molecular distribution functions  1.4.3. Boltzmann Distribution  1.4.4. Bose–Einstein and Fermi–Dirac statistics  1.5. Spectroscopy  1.5.1. Rotational Spectroscopy  1.5.2. Vibrational Spectroscopy  1.5.3. Electronic Spectroscopy  1.5.4. Nuclear magnetic resonance spectroscopy  1.5.5. Mass Spectrometry  1.5.6. Raman Spectroscopy  1.5.7. Electron paramagnetic resonance spectroscopy  1.6. Surface and colloidal chemistry  1.6.1. Absorption isotherm  1.6.2. Surface tension and wetting  1.6.3. Colloidal Stability  1.6.4. Catalysis  1.6.5. Emulsions and micelles  1.7. Electrochemistry  1.7.1. Nernst equation  1.7.2. Electrochemical cells  1.7.3. Conductivity and mobility  1.7.4. War  1.7.5. Fuel cells  1.7.6. Electrolysis
  2. Organic chemistry  2.1. Reaction mechanism  2.1.1. Nucleophilic substitution reactions  2.1.2. Electrophilic addition reactions  2.1.3. Elimination reactions  2.1.4. Rearrangement reactions  2.1.5. Radical reactions  2.1.6. Pericyclic reactions  2.2. Spectroscopy and structural determination  2.2.1. UV-Vis Spectroscopy  2.2.2. IR Spectroscopy  2.2.3. NMR Spectroscopy  2.2.4. Mass Spectrometry  2.2.5. X-ray crystallography  2.3. Stereoscopic  2.3.1. Chirality and optical activity  2.3.2. Structural analysis  2.3.3. Geometrical isomerism  2.3.4. Dynamic Stereochemistry  2.4. Organometallic Chemistry  2.4.1. Organolithium and organomagnesium reagents  2.4.2. Palladium-catalyzed cross-coupling reactions  2.4.3. Transition Metal Complexes  2.4.4. Metal–carbon bond  2.5. Polymer chemistry  2.5.1. Polymerization mechanism  2.5.2. Polymer Characteristics  2.5.3. Biodegradable Polymer  2.5.4. Conducting polymer  2.5.5. Supramolecular polymers  2.6. Medicinal chemistry  2.6.1. Drug design and development  2.6.2. Pharmacokinetics and pharmacodynamics  2.6.3. Structure-activity relationships  2.6.4. Molecular docking and drug screening
  3. Inorganic chemistry  3.1. Coordination chemistry  3.1.1. Crystal field theory  3.1.2. Ligand field theory  3.1.3. Spectrochemical Series  3.1.4. Chelation and stability  3.2. Organometallic Chemistry  3.2.1. Metal Carbonyls  3.2.2. Catalysis by organometallic complexes  3.2.3. Metallocenes  3.3. Bio-inorganic chemistry  3.3.1. Metalloproteins and enzymes  3.3.2. The role of metals in biological systems  3.3.3. Metal ion transport and storage  3.4. Solid state chemistry  3.4.1. Crystal Structures  3.4.2. Band theory of solids  3.4.3. Superconductors  3.4.4. Defects in the crystal  3.5. Lanthanides and Actinides  3.5.1. Electronic configuration in lanthanides and actinides  3.5.2. Coordination chemistry of the lanthanides  3.5.3. Magnetic Properties of Lanthanides
  4. Analytical chemistry  4.1. Chromatography  4.1.1. Gas Chromatography  4.1.2. High Performance Liquid Chromatography  4.1.3. Thin Layer Chromatography  4.2. Spectroscopic Techniques  4.2.1. Atomic absorption spectroscopy  4.2.2. X-ray diffraction  4.2.3. Inductively coupled plasma spectroscopy  4.3. Electroanalytical methods  4.3.1. Potentiometry  4.3.2. Voltammetry  4.3.3. Colometry  4.4. Mass Spectrometry  4.4.1. Ionization Technique  4.4.2. Fragmentation Pattern  4.5. Chemometrics  4.5.1. Multidisciplinary analysis  4.5.2. Machine Learning in Chemistry
  5. Theoretical and Computational Chemistry  5.1. Molecular dynamics simulation  5.1.1. Force fields and energy minimization  5.1.2. Monte Carlo simulation in molecular dynamics simulations  5.2. Quantum chemical methods  5.2.1. Hartree–Fock theory  5.2.2. Density functional theory  5.2.3. Semi-empirical methods  5.3. Computational drug design  5.3.1. Molecular Docking  5.3.2. QSAR Modeling  5.3.3. Virtual Screening
  6. Biochemistry  6.1. Enzyme Kinetics  6.1.1. Michaelis-Menten kinetics  6.1.2. Inhibition mechanism  6.2. Metabolism and Bioenergetics  6.2.1. Glycolysis  6.2.2. Citric acid cycle  6.2.3. Electron transport chain  6.3. molecular Biology  6.3.1. DNA replication and repair  6.3.2. Protein synthesis  6.3.3. Gene Regulation  6.4. Structural Biochemistry  6.4.1. Protein Folding  6.4.2. Membrane Biophysics
  7. Environmental Chemistry  7.1. Atmospheric Chemistry  7.1.1. Greenhouse gases  7.1.2. Ozone depletion  7.1.3. Air pollutants and smoke  7.2. Water Chemistry  7.2.1. pH and water hardness  7.2.2. Wastewater treatment  7.2.3. Aquatic Chemistry  7.3. Soil Chemistry  7.3.1. Heavy metal contamination  7.3.2. Soil pH and Buffering  7.3.3. Nutrient cycling  7.4. Toxicology and Chemical Safety  7.4.1. Toxicokinetics  7.4.2. Risk Assessment in Toxicology and Chemical Safety in Environmental Chemistry  7.4.3. Effects of pollutants on the environment

Graduate → Inorganic chemistry → Coordination chemistry ↓


Spectrochemical Series


Coordination chemistry is a fascinating branch of inorganic chemistry that focuses on the study of compounds that form between metal ions and ligands. An important concept within this field is the "spectrochemical series," a list of common ligands ranked according to their ability to split the d-orbitals of the central metal ion in a complex. This splitting affects the electronic properties of the complex and can influence its color, stability, and reactivity. In this comprehensive guide, we will delve deep into the specifics of the spectrochemical series, its origins, its importance, and its applications.

Definition of spectrochemical series

The spectrochemical series is a sequence that ranks ligands according to their strength in terms of their field strength or crystal field splitting parameter (Δ). More simply, it classifies ligands ranging from those that produce a small splitting of d-orbitals to those that cause a large splitting. This series is important for predicting the geometry and colour of coordination compounds.

        Weak field ligands: I -, Br -, Cl -, F -, OH -, C 2 O 4 2-, H 2 O
        
        Intermediate ligand: NCS-, NH3, N(ethylenediamine)

        Strong field ligands: NO 2 -, CN -, CO

It is important to understand that spectrochemical series provide only general trends. The exact state of the ligand may vary depending on the metal ion to which it is attached, the oxidation state of the metal, and other factors.

Origin and historical context

The concept of spectrochemical series emerged from studies on the electronic spectra and magnetic properties of coordination complexes. These studies took place in the early 20th century when researchers such as Alfred Werner began exploring the nature of coordination compounds. Later, more sophisticated techniques such as UV-Vis spectroscopy and magnetic susceptibility strengthened the understanding and validation of spectrochemical series.

Theoretical background

Crystal field theory

Central to the spectrochemical series is crystal field theory (CFT), which describes how the degeneracy of metal d-orbitals is affected by the presence of surrounding ligands. According to CFT:

  • Repulsion arises as the ligand electrons approach the central metal ion, resulting in the splitting of the degenerate d-orbitals into different energy levels.
  • In an octahedral field, the d-orbitals split into two sets: lower-energy t 2g (d xy, d xz, d yz) and higher-energy e g (d x 2 -y 2, d z 2) orbitals.
         e.g.
         | Δ
         T2G

The magnitude of Δ (crystal field splitting energy) determines whether a ligand is a weak field ligand or a strong field ligand.

Ligand field theory

Ligand field theory (LFT) is based on CFT by incorporating molecular orbital theory. This theory takes into account covalent interactions between metal ions and ligands, providing a more comprehensive explanation of bonding and electronic properties. LFT considers both σ and π interactions, which can increase or decrease the splitting depending on the nature of the ligand.

Factors affecting the spectrochemical series

Several factors affect where a ligand falls in the spectrochemical series:

Nature of metal ion

The type of metal, its oxidation state, and electronic configuration can all affect the effect a ligand has on d-orbital splitting. Transition metals with higher oxidation states generally produce higher crystal field splitting energies.

Complex geometry

The geometry of a complex affects how the d-orbitals are split. For example, in a tetrahedral field, the d-orbitals are split in the opposite way than in an octahedral complex.

         T2G
        | Δ
         e.g.

The concept of high-spin and low-spin complexes exists mainly in octahedral geometry.

Electronic properties of the ligand

Ligands with π-donor and π-acceptor potentials can change their positions within the spectrochemical series. For example, ligands with π-acceptor potentials such as CO are strong field ligands.

Applications of spectrochemical series

Understanding the spectrochemical series has real-world applications in the following areas:

Catalysis

The nature of ligand coordination affects the catalytic activity and selectivity of metal-centered catalysts. Strong field ligands can influence catalytic cycles by stabilizing particular oxidation states or intermediates.

Bio-inorganic chemistry

In biological systems, metal ions coordinated to biomolecules often display unique electronic properties that are important for functions such as oxygen transport, electron transfer, and enzymatic activity. The spectrochemical properties of biological metal centers can explain their function and reactivity.

Colour of complexes

The color seen in coordination compounds arises due to d-d transitions, which are strongly affected by the magnitude of the crystal field splitting. Weak field ligands result in small splittings, often producing light-colored complexes, while strong field ligands result in large splittings, often resulting in rich and deep colors.

Examples of spectrochemical series

Example 1: Predicting spin states

Consider the complex [Fe(H 2 O) 6 ] 3+. Water is a weak field ligand, so the complex forms a high-spin state. In contrast, [Fe(CN) 6 ] 3- forms a low-spin state with cyanide (a strong field ligand).

Example 2: Understanding color change

The purple colour of [Cr(H 2 O) 6 ] 3+ is in contrast to the orange-red colour of [Cr(NH 3 ) 6 ] 3+. This transition from a weak field ligand to a medium strength ligand results in a changed d-d transition and thus a different colour.

Conclusion

The spectrochemical series is a fundamental concept in coordination chemistry, providing profound insights into the electronic properties of metal complexes. By understanding this series, chemists can predict not only the geometry and colour of the complexes but also their reactivity and stability. Knowing the location of a ligand in the spectrochemical series facilitates tailored synthesis of coordination compounds for desired applications, making it an important tool in modern inorganic chemistry.


Graduate → 3.1.3


U
username
0%
completed in Graduate

← Prev (3.1.2)
Ligand field theory
Next (3.1.4) →
Chelation and stability

Comments 



Spectrochemical Series

https://www.chemistryelite.com/g/3.1.3?ceal=en