What makes a ligand strong field




















You observe that the cyanide ion is a better ligand than the nitrogen ligand. Let's think about this. The lone pair that reacts on the cyanide ion is the lone pair on the carbon atom. Not the lone pair on the nitrogen atom. Carbon is less electronegative than nitrogen. Thus carbon is less able to stabilize its valence electron density, which in turns enhances the reactivity of its valence electron density through increased negative charge density.

Same with sulfide and oxide anions. Sulfur is less electronegative than oxygen, and thus less able to stabilize valence electron density. Hence the much greater stability of silver sulfide as opposed to silver oxide. Other competing factors include charge density; the Lewis acid the ligand is coordinating to, medium solvent , etc.

For example the oxide anion is more basic than the sulfide anion in water solvent; i. But we just saw that silver sulfide is much more stable than silver oxide. Being lewis bases those who donate electrons the ligands with less electronegativity will be stronger. According to crystal field theory and spectrochemical series, PPh3 is a strong field ligand because it will produce strong splitting.

EDTA is a moderately strong field, while en is a strong field ligand. Water is a weak field ligand. The electronegative O atom is strongly electron-withdrawing, so there is poor orbital overlap between the electron pair on O and a metal d-orbital.

The more electropositive C atom in the strong field ligand CN - allows better orbital overlap and sharing of the electron pair. In the event that there are two metals with the same d electron configuration, the one with the higher oxidation state is more likely to be low spin than the one with the lower oxidation state.

It is then classified as low spin because there is a minimal amount of unpaired electrons. C2O4 is a weak field ligand. It causes a small splitting of energy levels. Hence, it is energetically more favorable for the electrons to occupy eg level instead of pairing up with t2g level. Usually, electrons will move up to the higher energy orbitals rather than pair. Because of this, most tetrahedral complexes are high spin. From Wikipedia, the free encyclopedia. Ligand field theory LFT describes the bonding, orbital arrangement, and other characteristics of coordination complexes.

It represents an application of molecular orbital theory to transition metal complexes. NO3 - Nitrate ion is not an ambidenate ligand. But NO2- Nitrite ion is an ambidentate ligand. In a square planar, there are four ligands as well.

There are four different energy levels for the square planar from the highest energy level to the lowest energy level : d x 2 -y 2 , d xy , d z 2 , and both d xz and d yz. For the complex ion [Fe Cl 6 ] 3- determine the number of d electrons for Fe, sketch the d-orbital energy levels and the distribution of d electrons among them, list the number of lone electrons, and label whether the complex is paramagnetic or diamagnetic.

A tetrahedral complex absorbs at nm. What is the color of the complex? This is the energy needed to promote one electron in one complex. This complex appears red, since it absorbs in the complementary green color determined via the color wheel. For each of the following, sketch the d-orbital energy levels and the distribution of d electrons among them, state the geometry, list the number of d-electrons, list the number of lone electrons, and label whether they are paramagnetic or dimagnetic:.

Tetrahedral Geometries. Robert J. Basic Concept In Crystal Field Theory, it is assumed that the ions are simple point charges a simplification. Attractive electrostatic interactions between the negatively charged ligands and the positively charged metal ion far right cause all five d orbitals to decrease in energy but does not affect the splittings of the orbitals. The two e g orbitals point directly at the six negatively charged ligands, which increases their energy compared with a spherical distribution of negative charge.

In contrast, the three t 2g orbitals point between the negatively charged ligands, which decreases their energy compared with a spherical distribution of charge. The strong field is a low spin complex, while the weak field is a high spin complex. Description of d -Orbitals To understand CFT, one must understand the description of the lobes: d xy : lobes lie in-between the x and the y axes.

Octahedral Complexes In an octahedral complex , there are six ligands attached to the central transition metal. Tetrahedral Complexes In a tetrahedral complex, there are four ligands attached to the central metal. What is Strong Ligand 4. What is Weak Ligand 5.

Crystals field theory can be described as a model that is designed to explain the breaking of degeneracies electron shells of equal energy of electron orbitals usually d or f orbitals due to the static electric field produced by a surrounding anion or anions or ligands.

This theory is often used to demonstrate the behaviour of transition metal ions complexes. This theory can explain the magnetic properties, colours of coordination complexes, hydration enthalpies, etc. The interaction between the metal ion and ligands is a result of the attraction between the metal ion with a positive charge and the negative charge of the unpaired electrons of the ligand. This theory is mainly based on the changes occuring in five degenerated electron orbitals a metal atom has five d orbitals.

When a ligand come close to the metal ion, the unpaired electrons are closer to some d orbitals than that of other d orbitals of the metal ion. This cause a loss of degeneracy. And also, the electrons in the d orbitals repel the electrons of the ligand because both are negative charged.

Hence the d orbitals that are closer to the ligand has high energy than that of other d orbitals. This result in the splitting of d orbitals into high energy d orbitals and low energy d orbitals, based on the energy.



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