The infulence of ligands in complexes

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In summary, the conversation discusses the trend observed in metal chemical shifts for complex formulas containing transition metal M, with the order M > CN > Br > NH3 > NO2 > Cl > H2O. This trend is also observed for similar complexes with formulas Pd(R)3Cl, Pd(NH3)2X2, and Pd(R)Cl3. The trend shows that the metal signal is more shielded when the ligand is less electronegative and larger, possibly due to backdonation of electrons from the ligand to the metal. The conversation also mentions the nephelauxetic effect, which is a lowering of the Racah B parameter caused by partial covalency in the
  • #1
KarolinaPL
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Hello! I analise metal chemical shifts, its formula is MR4, where M is transition metal, like Palladium,
and there is some trend:

I > CN > Br > NH3 > NO2 > Cl > H2O,

the same trend is observed for similar complex of formula: Pd(R)3Cl, Pd(NH3)2X2, Pd(R)Cl3
So, the metal signal shielding increase in order showed below... I noticed, the less electronegative and bigger halogen ion as ligand, the chemical shift of metal, like palladium, is more shielded. It is probably caused by backdonation of electrons from ligand towards metal. What about the other ligands? For example, NH3 is "less electronegative" ligand than H2O, so lone pair on nitrogen may donate electrons? bond metal-OH2 is more ionic probably, and electrons are shiftes slightly more to oxygen than metal... What about CN, NO2? What can be the effect of this trend? which properties of those ligands may influence chemical shift? it is usually influenced by donation/withdrawing of electrons and so on... polarizability?
 
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I apologize, I'm having a little bit of trouble understanding your English. Just to clarify: the series you give (I, CN, Br, etc) goes from a PdNMR signal that is more shielded (further upfield) to less shielded (further downfield)? You might want to look at the nephelauxetic effect. It's basically a lowering of the Racah B parameter due to partial covalency of the coordinate bond between a ligand and a metal. The series for the nephelauxetic effect is pretty close to the one you've given.
 
  • #3
Yes
 

FAQ: The infulence of ligands in complexes

1. What is a ligand?

A ligand is a molecule or ion that binds to a central atom or ion to form a complex. It typically has at least one lone pair of electrons that can be donated to the central atom.

2. How do ligands affect the properties of a complex?

Ligands can greatly influence the physical and chemical properties of a complex, such as its color, stability, and reactivity. The type and number of ligands can also affect the geometry and electronic structure of the complex.

3. What is the role of ligands in metal complexes?

Ligands play a crucial role in the formation and stability of metal complexes. They help to stabilize the central metal ion by providing a coordination sphere and also determine the overall charge and reactivity of the complex.

4. How do ligands bind to a central atom in a complex?

Ligands can bind to a central atom through various types of interactions, including coordinate covalent bonds, hydrogen bonds, and electrostatic interactions. The binding strength depends on the nature of the ligand and the central atom.

5. What factors influence the choice of ligands in a complex?

The choice of ligands in a complex is influenced by a variety of factors, including the size and charge of the central atom, the desired geometry of the complex, and the specific properties or functions that are desired for the complex.

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