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By the end of this section, you will be able to:
  • Outline the basic premise of crystal field theory (CFT)
  • Identify molecular geometries associated with various d-orbital splitting patterns
  • Predict electron configurations of split d orbitals for selected transition metal atoms or ions
  • Explain spectral and magnetic properties in terms of CFT concepts

The behavior of coordination compounds cannot be adequately explained by the same theories used for main group element chemistry. The observed geometries of coordination complexes are not consistent with hybridized orbitals on the central metal overlapping with ligand orbitals, as would be predicted by valence bond theory. The observed colors indicate that the d orbitals often occur at different energy levels rather than all being degenerate, that is, of equal energy, as are the three p orbitals. To explain the stabilities, structures, colors, and magnetic properties of transition metal complexes, a different bonding model has been developed. Just as valence bond theory explains many aspects of bonding in main group chemistry, crystal field theory is useful in understanding and predicting the behavior of transition metal complexes.

Crystal field theory

To explain the observed behavior of transition metal complexes (such as how colors arise), a model involving electrostatic interactions between the electrons from the ligands and the electrons in the unhybridized d orbitals of the central metal atom has been developed. This electrostatic model is crystal field theory    (CFT). It allows us to understand, interpret, and predict the colors, magnetic behavior, and some structures of coordination compounds of transition metals.

CFT focuses on the nonbonding electrons on the central metal ion in coordination complexes not on the metal-ligand bonds. Like valence bond theory, CFT tells only part of the story of the behavior of complexes. However, it tells the part that valence bond theory does not. In its pure form, CFT ignores any covalent bonding between ligands and metal ions. Both the ligand and the metal are treated as infinitesimally small point charges.

All electrons are negative, so the electrons donated from the ligands will repel the electrons of the central metal. Let us consider the behavior of the electrons in the unhybridized d orbitals in an octahedral complex. The five d orbitals consist of lobe-shaped regions and are arranged in space, as shown in [link] . In an octahedral complex, the six ligands coordinate along the axes.

This figure includes diagrams of five d orbitals. Each diagram includes three axes. The z-axis is vertical and is denoted with an upward pointing arrow. It is labeled “z” in the first diagram. Arrows similarly identify the x-axis with an arrow pointing from the rear left to the right front, diagonally across the figure and the y-axis with an arrow pointing from the left front diagonally across the figure to the right rear of the diagram. These axes are similarly labeled as “x” and “y.” In this first diagram, four orange balloon-like shapes extend from a point at the origin out along the x- and y- axes in positive and negative directions covering just over half the length of the positive and negative x- and y- axes. Beneath the diagram is the label, “d subscript ( x superscript 2 minus y superscript 2 ).” The second diagram just right of the first is similar except the x, y, and z labels have been replaced in each instance with the letter L. Only a pair of the orange balloon-like shapes are present and extend from the origin above and below along the vertical axis. An orange toroidal or donut shape is positioned around the origin, oriented through the x- and y- axes. This shape extends out to about a third of the length of the positive and negative regions of the x- and y- axes. This diagram is labeled, “d subscript ( z superscript 2 ).” The third through fifth diagrams, similar to the first, show four orange balloon-like shapes. These diagrams differ however in the orientation of the shapes along the axes and the x-, y-, and z-axis labels have each been replaced with the letter L. Planes are added to the figures to help show the orientation differences with these diagrams. In the third diagram, a green plane is oriented vertically through the length of the x-axis and a blue plane is oriented horizontally through the length of the y-axis. The balloon shapes extend from the origin to the spaces between the positive z- and negative y- axes, positive z- and positive y- axes, negative z- and negative y- axes, and negative z- and positive y- axes. This diagram is labeled, “d subscript ( y z ).” In the fourth diagram, a green plane is oriented vertically through the x- and y- axes and a blue plane is oriented horizontally through the length of the x-axis. The balloon shapes extend from the origin to the spaces between the positive z- and negative x- axes, positive z- and positive x- axes, negative z- and negative x- axes, and negative z- and positive x- axes. This diagram is labeled “d subscript ( x z ).” In the fifth diagram, a pink plane is oriented vertically through the length of the y-axis and a green plane is oriented vertically through the length of the x-axis. The balloon shapes extend from the origin to the spaces between the positive x- and negative y- axes, positive x- and positive y- axes, negative x- and negative y- axes, and negative x- and positive y- axes. This diagram is labeled, “d subscript ( x y ).”
The directional characteristics of the five d orbitals are shown here. The shaded portions indicate the phase of the orbitals. The ligands (L) coordinate along the axes. For clarity, the ligands have been omitted from the d x 2 y 2 orbital so that the axis labels could be shown.

In an uncomplexed metal ion in the gas phase, the electrons are distributed among the five d orbitals in accord with Hund's rule because the orbitals all have the same energy. However, when ligands coordinate to a metal ion, the energies of the d orbitals are no longer the same.

Questions & Answers

whats de shape of water
Amara Reply
water has no shape because it's liquid
Wil
water is a shapeless, odourless, colourless and tasteless substance that only takes the shape of its container.
mikefred
i think they're referring to the molecular shape?
It has no shape but takes the shape of the container
kpadonu
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Wilson Reply
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noble
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marwan Reply
Yes?
Esther
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noble
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noble
is euglena a unicellular organ
Agio Reply
is euglena a unicellular organism
Agio
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Buwembo Reply
what is difference between atom and molecule
Aqeela Reply
Atom is the smallest part of matter; it consists of equal number of protons and electrons. It may have neutrons. A molecule is a compound made of atoms covalently bonded.
Abdelkarim
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Mercy Reply
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kolawole Reply
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kolawole
what's an atom?
Davy Reply
it's the smallest unit of Matter
Orsine
atom
Eden
smallest part of an element
lydia
also, depending on its (atom's) structure, that is the amount of protons and neutrons and electrons, is the determining factors of what element it is.
Richard
is a smallast particals of an element
Buwembo
it is the smallest part of an element that can take part in a chemical reaction
Ayub
is the smallest part of an element
Jonathan
An atom is the smallest indivisible part of a matter
kpadonu
Oy kl konsa test hay or kitna hay?
Faisal Reply
differences between solid liquid and gaseous state
Ochei Reply
modification of John dalton atomic theory
Ochei
the differences between soliq liquid and gas is that in solid the particle are strongly bonded together by forces of cohesion and the particle are not able to move about but only vibrate in a fixed position but in liquid the particle are loosely bond together and the particle are able to move about
kolawole
2.4g of magnesium reacts with 0.3mol of hydrochloric acid write a balanced chemical equation for the reaction. (b)Determine the limiting reactant
Sheldon Reply
I don't understand internal heat energy and Hess' law...
Jo Reply
Internal energy is the sum of kinetic and potential energies a substance or a mass of material posses. Hess law is about that (he found out) that whatever the reaction direction or steps (routes) the reactants take to rwach the same product have the same resultant enthalpy change (enthalpy is simply
Abdelkarim
The exchange of energy between 1 mole of reactants and surrounding.)
Abdelkarim
Energy is simply a measurment for how much work can be done; like, if I have 5 joules I can run 5 meters and if I have 10 joules of energy I can run 10 metres for examole. Energy is something that we can't touch nor create nor detroy, only god (the first) can do that..
Abdelkarim
what is the functionally group of alkanol
Agbo
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Aliyu Reply
Knowledge of organic chemistry is revolutionising for many aspects of our life and for conservation of animals in habitat as well. It is essential for the developing of new drugs for new diseases. Important in industry of food flavours/ additives, paints, colours, materials (like plastic for its)
Abdelkarim
Suitable needs), and still research can open new fields in what we still don't know and in application.
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Prophet Mohamed said pbuh in explanation (God did not create a disease except create a cure for it. ) could also be psychological.
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Source:  OpenStax, Chemistry. OpenStax CNX. May 20, 2015 Download for free at http://legacy.cnx.org/content/col11760/1.9
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