Which of the following complex is/are low spin complexes? (2024)

FAQs

Which of the following complex is low spin complex? ›

Since CN− and NH3 are strong field ligands (from spectrochemical series) so [Fe(CN)6]4− and [Co(NH3)6]3+ are low spin complexes. Conversely, F− and H2O are weak field ligands and thus [CoF6]3− and [Fe(H2O)6]2+ are high spin complexes.

For biological ligands, H2O and NH3, the most stable spin state is high spin (S ) 3/2). The difference in energy between high and low spin is dependent upon the ligand mix and coordination stereochemistry. High spin optimized geometries for these model compounds give structures close to octahedral symmetry.

Another method to determine the spin of a complex is to look at its field strength and the wavelength of color it absorbs. If the field is strong, it will have few unpaired electrons and thus low spin. If the field is weak, it will have more unpaired electrons and thus high spin.

High Spin and Low Spin

The complexion with the greater number of unpaired electrons is known as the high spin complex, the low spin complex contains the lesser number of unpaired electrons. High spin complexes are expected with weak field ligands whereas the crystal field splitting energy is small Δ.

In an octahedral complex, when Δ is large (strong field ligand), the electrons will first fill the lower energy d orbitals before any electrons are placed on the higher energy d orbitals. It is then classified as low spin because there is a minimal amount of unpaired electrons.

The usual Hund's rule and Aufbau Principle apply. Examples of low-spin d6 complexes are [Cr(CN)6]3− and Cr(CO)6 , and examples of high-spin d6 complexes are [CrCl6]3− and Cr(H2O)6 .

The low-spin state of octahedrally coordinated Co³⁺ ions is more stable than the high-spin state because of the exceptionally high crystal field stabilization energy due to completely filled 3d t_2g orbitals [38].

Lower oxidation state of metal favours the formation of high spin complex unless ligand is highly strong field ligand. NH3 is not very strong field ligand therefore [Fe(NH3)6]++ is sp3d2 (high spin complex).

Explanation: The complex given here is [Co(NH3)6]3+ The complex has sp³d² hybridization which means 4d, 4s, and 4p orbitals of Cobalt are involved and the cation has +3 charge. The ligand ammonia is a strong field ligand and forms low spin complexes.

It is rare for the Δt of tetrahedral complexes to exceed the pairing energy. Usually, electrons will move up to the higher energy orbitals rather than pair. Because of this, most tetrahedral complexes are high spin.

Why are low spin complexes not found? ›

Low spin tetrahedral complexes are not formed because for tetrahedral complexes, the crystal field stabilization energy is lower than pairing energy.

The octahedral complex ions [FeCl6]3− and [Fe(CN)6]3− are both paramagnetic but the former is high spin and the latter is low spin.

If cystal field splitting energy (difference of energy between t2g and eg orbitals) is large, low spin state is more stable and if it is small, high spin state is more stable.

Iron(II) has the 3d⁶ outer electronic configuration and hence its octahedral complexes may be either high-spin or low-spin. The high-spin configuration, t ⁴_2g e ²_g , is adopted when relatively weak-field ligands are coordinated while the low-spin, t ⁶_2g e ⁰_g , is obtained when strong-field ligands are involved.

Low-spin complexes contain more paired electrons because the splitting energy is larger than the pairing energy. These complexes, such as [Fe(CN)₆]^3-, are more often diamagnetic or weakly paramagnetic.

d2sp3 is inner shell complex which is also known as low spin complex, having participation of inner d orbitals in hybridization along with s and p orbitals. For Example: 3 d , 4s and 4p will combine and form d2sp3 .

[FeF6]3− is a high spin complex and contains 5 unpaired electrons. Hence it is paramagnetic.

Strong-field ligands, such as CN⁻ and CO, increase the Δ splitting and are more likely to be low-spin. Weak-field ligands, such as I⁻ and Br⁻ cause a smaller Δ splitting and are more likely to be high-spin.

Hence, the orbital splitting energies are not enough to force pairing. As a result, low spin configurations are rarely observed in tetrahedral complexes and the low spin tetrahedral complexes not form.