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Home > Articles > Spectrochemical Series Explained: Ligands, Color, and Metal Complexes in Chemistry
Spectrochemical Series Explained: Ligands, Color, and Metal Complexes in Chemistry
Nikita Parmar
Updated on 23rd August, 2024 , 5 min read
Spectrochemical Series: Comprehensive Overview
A spectrochemical series consists of a set of ligands arranged in ascending order of "strength" and a set of metal ions arranged in ascending order of element, oxidation group, and number. Based on how well ligands interact with metal ions, a method of classification known as the spectrochemical series has been developed. A key factor in deciding whether a transition metal complex has a high or low spin is the kind of ligands present. The d orbital energy splitting is influenced by the intensity of the ligand-metal interaction. Relatively moderate interactions between ligands change the d orbital energy levels just a little, whereas strong interactions between ligands significantly alter the d orbital energy levels. A shift in a band of the UV-Vis spectra happens when two similar complexes with two different ligands are compared, and this change gives birth to the spectrochemical series.
Spectrochemical Series: What is a Spectrochemical Series?
A spectrochemical series is a list of ligands arranged according to their "strength" and a list of metal ions arranged according to their element, oxidation number, and group. The ligands for a metal ion alter what is known as the crystal-field splitting parameter in crystal field theory or the ligand-field splitting parameter in ligand field theory as the energy difference between the d orbitals. The splitting parameter affects the ion's electronic and magnetic characteristics, such as its spin state, and optical properties, such as its color and absorption spectrum. On this list, the common ligands are listed in increasing order of ligand field strength-
According to "the spectrochemical series," it is basically the opposite of what it should be for a reasonable forecast based on crystal field theory's suppositions.
Spectrochemical Series: Who invented the Spectrochemical Series?
Shimura (1988) first proposed the Spectrochemical Series of the ligands based on experimental data and in good agreement with numerous qualitative studies that demonstrate the same order to explain the crystal field splitting between the eg (dz2, dx2-y2) and t2g (dxy, dxz, dyz) orbitals in transition metals.
Spectrochemical Series: History of Spectrochemical Series
In 1938, the spectrochemical series was created. This series is based on the findings of the cobalt complexes' absorption spectra. Essentially, this series is a collection of ligands that have been classified or categorized according to strength.
Spectrochemical Series: Spectrochemical Series of Ligands
Below is a list of the ligands in the spectrochemical series, ordered from small to large-
Spectrochemical Series: Spectrochemical Series of Metals
Additionally, various metal ions can be arranged in ascending order, which is as follows-
Spectrochemical Series: Factors Affecting the Spectrochemical Series
The following are some of the factors affecting the spectrochemical series-
- Despite being experimentally determined, the series is challenging to theoretically explain.
- The relative position, nevertheless, is determined by their growing contribution.
- The strongest ligands in the series are those with a high negative charge, a small size, good donor and acceptor properties, and substantial crystal field splitting. In contrast, weak field ligands that function as -donors occupy the bottom position.
Read more about the Father of Chemistry and the Chemistry Periodic Table.
Spectrochemical Series: Significance of Spectrochemical Series
The following points highlight the importance of the electrochemical series-
- The relative d-orbital splitting of two complexes containing the same metal ion with various ligands may be predicted using spectrochemical series.
- Similar to that, it is possible to anticipate the relative frequency of the absorption band.
Spectrochemical Series: Limitations of Spectrochemical Series
The spectrochemical series makes pure crystal field theory interpretation extremely challenging. Here is a list of some of the restrictions of spectrochemical series-
- Although their dipole moments are in reverse order, NH3 splits more than H2O.
- The effects would be greatest for anionic ligands, although they are at the low end.
- The model also fails to explain why, for comparable complexes within a group, o only minimally fluctuates for some strong field ligands (like CN-).
- The sequence is reversed even though neutral H2O should be above OH-.
Read more about the Electrochemical Series.
Spectrochemical Series: Uses of Spectrochemical Series
The following are some of the uses of spectrochemical series-
- It is also possible to forecast the absorption band's relative frequency.
- The relative d-orbital splitting of two complexes containing the same metal ion with various ligands may be predicted using this series.
| Spectrochemical Series FAQs |
| Q. What is the spectrochemical series? |
| A. A list of ligands, or attachments to metal ions, sorted according to field strength is called the spectrochemical series. Several sequences obtained from spectroscopic research have been overlapped to generate the series, which cannot be formed by investigating complexes with a single metal ion. |
| Q. Can CFT explain spectrochemical series? |
| A. The relevance of the spectrochemical series is explained by crystal field theory, or CFT, which also explains how ligands influence the energy levels of degenerate orbitals in coordination complexes, which are orbitals with multiple unique, quantifiable energy states. |
| Q. What is the strongest ligand series? |
| A. The right response is CN-. Because it has the highest Δ value of all the supplied ligands, the CN- (negative) ligand is a strong field ligand. Any ligand's potency is based on its crystal field theory (CFT) content. |
| Q. Why is CO a strong ligand? |
| A. Coordination bonds with sigma and pi characteristics are formed by CO. The primary bond is formed by a non-bonding orbital on the CO, while a secondary bond is formed by an anti-bonding orbital. The energy splitting is very high and the carbonyl-metal bond is particularly strong due to this multiple coordination bond. |
| Q. Is NO2 a strong or weak ligand? |
| A. Low spin complexes and significant splittings between the d orbitals are characteristics of strong field ligands. Strong field ligands are CO, CN-, and NO2-, for instance. |
Spectrochemical Series: Conclusion
A list of ligands arranged by strength, or a list of metal ions arranged by oxidation number, group, and element, makes up the spectrochemical series, which first appeared in 1938. In crystal field theory, ligands change the energy disparity between d orbitals, a phenomenon known as crystal field splitting. While ligands often give electrons away, metals tend to receive them. Weak field ligands and strong field ligands are the two types of ligands. On the other hand, weak field ligands are those that have little crystal field splitting and provide high values. Low spin values are the result of strong field ligands' significant crystal field splitting.
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Frequently Asked Questions
Describe the spectrochemical series foundation.
Ans. The spectrochemical series' foundation is the interaction of metal and ligand. The splitting of d-orbitals increases with the size of the ligand-metal contact, which in turn results in a stronger pairing.
What are the uses of spectrochemical series?
Ans. It is also possible to forecast the absorption band's relative frequency and the relative d-orbital splitting of two complexes containing the same metal ion with various ligands using this series.
What is the definition of a spectrochemical series?
Ans. The term "spectrochemical series" refers to the arrangement of ligands in a series in the order of increasing crystal field splitting.
What are the spectrochemical series limitations?
Ans. The influence would be greatest from the anionic ligands, although they are at the low end of the range. The approach also ignores the fact that delta o very slightly differs across analogous complexes within a group for some strong field ligands (like CN-).
Who proposed the spectrochemical series?
Ans. Shimura (1988) is the one who first proposed the Spectrochemical Series.