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Weak field ligands: H 2 O, F −, Cl −, OH −. Strong field ligands: CO, CN −, NH 3, PPh 3. Ligands arranged on the left end of this spectrochemical series are generally regarded as weaker ligands and cannot cause forcible pairing of electrons within the 3d level, and thus form outer orbital octahedral complexes that are high spin. Ligands ...
As described above, π-donor ligands lead to a small Δ O and are called weak- or low-field ligands, whereas π-acceptor ligands lead to a large value of Δ O and are called strong- or high-field ligands. Ligands that are neither π-donor nor π-acceptor give a value of Δ O somewhere in-between.
The magnitude of Δ o is determined by the field-strength of the ligand: strong field ligands, by definition, increase Δ o more than weak field ligands. Ligands can now be sorted according to the magnitude of Δ o (see the table below). This ordering of ligands is almost invariable for all metal ions and is called spectrochemical series.
High Spin [FeBr 6] 3− crystal field diagram. Conversely, ligands (like I − and Br −) which cause a small splitting Δ of the d-orbitals are referred to as weak-field ligands. In this case, it is easier to put electrons into the higher energy set of orbitals than it is to put two into the same low-energy orbital, because two electrons in ...
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. Some octahedral complexes exhibit spin crossover, where the high and low spin states exist in dynamic equilibrium.
Transition metal complexes of thiocyanate describes coordination complexes containing one or more thiocyanate (SCN −) ligands. The topic also includes transition metal complexes of isothiocyanate. These complexes have few applications but played significant role in the development of coordination chemistry. [1]
Weak field ligands, as judged by the spectrochemical series, favor tetrahedral geometry and strong field ligands favor the square planar isomer. Both weak field (Cl −) and strong field (PPh 3) ligands comprise NiCl 2 (PPh 3) 2, hence this compound is borderline between the two geometries.
Halides are X-type ligands in coordination chemistry. They are both σ- and π-donors. Chloride is commonly found as both a terminal ligand and a bridging ligand. The halide ligands are weak field ligands. Due to a smaller crystal field splitting energy, the homoleptic halide complexes of