Pentacoordination of Zinc: A Possibility or a Myth?

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In summary, the conversation is discussing the possibility of zinc (II) ions coordinating with five ligands, potentially creating a tetragonal monopyramidal environment. There are doubts about this due to the d10 electronic configuration and crystal field theory. The conversation also touches on the calculation of stability energy and the use of data from a table to determine the possibility of pentacoordination. It is suggested that classical construction and perturbation theory would be necessary for an exact calculation.
  • #1
chem_tr
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Hello,

I've heard rumors (frankly, not rumors, evidenced by some scientific papers), that zinc(II) ion has coordinated five ligands, four at a plane, and the fifth from top, to form a tetragonal monopyramidal environment.

I have some doubts about this, because zinc (II) ion has d10 electronic configuration in normal circumstances, which means, according to crystal field theory, that octahedral stability energy is zero.

What are your comments?

chem_tr
 
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  • #2
Hi chem_tr,

Five ligands? Mmm... strange. It would be necessary to calculate the stability energy. Are the five ligands identical? I´ve found the degeneracy split pattern for a square piramidal geomety:
http://www.unine.ch/chim/chw/html%20files/CFSE%20geom.html [Broken]

Can you calculate the stability energy from this data? I´m not sure about it.
 
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  • #3
Hello altered-gravity,

Let me correct something first. There are four donors in a planar macrocyle (e.g., phthalocyanine), and the fifth one approaches from the perpendicular axis to the plane. There are also some examples in which zinc coordinates a pentadentate ligand, two thiolates, one pyridine nitrogen, and two azomethine nitrogens.

I will look through your table in detail, thank you for your interest.
 
  • #4
Biochemical complexes are too much for my POOR "ab initio power" :biggrin:

Anyway the case you are talkig about (phtalocyanine ring) is a square based piramidal geometry (C4v point group). In the table I post before, that geometry is supposed for five identical and simple ligands, and says that the degeneracy splits into four different energy levels, three monodegenerate and one doubly degenerate.

In your case, although much more complicated, the point group is the same. So we may think that the energy scheme is the same (four levels). The task is to calculate the system energy provided that there are 10 electrons and the spin is 0. I think that the energy would be like this:
[tex]E=\sum_{i} e_i -\sum_i \sum_{j>i} J_{ij} [/tex]

i: each electron
ei: energy of the level where "i" electron is
Jij: Coulomb integral of electrons "i" and "j"

I´m just speculating so don´t pay too much attention to me if you´re working seriously on this.
 
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  • #5
Hello,

C4v symmetry is valid for phthalocyanines, you are right. I have no idea about how to use these data on the table I downloaded from your post. Can you say that, by using the values on the table, it is possible/known for Zn to bind another ligand to reach pentacoordinated state?

My mathematics has left me a long time ago, so I cannot make any comments about your double-sigma-containing huge formula :smile:

Thank you for your interest
 
  • #6
chem_tr said:
Can you say that, by using the values on the table, it is possible/known for Zn to bind another ligand to reach pentacoordinated state?

Not exactly. That table gives you energies of the "d" orbitals for different geometries, but with ONLY ONE ligand type, for example Zn(OH)4 2-. From here you can calculate the square piramid geometry system energy, and compare it with others as planar square geom, in other words, the relative stability of the pentacoordinated. Then you can "imagine" or qualitatively approach the perturbation that the fifth ligand creates when it aproaches the square planar system.

The table gives energyes in terms of [tex]\Delta_0[/tex], this parameter is the energy perturbation of an octahedral geometry with the same ligand type, look at this:
http://chemed.chem.purdue.edu/genchem/topicreview/bp/ch12/crystal.html [Broken]
this parameter must be calculated for each ligand type.

For the phtalocyanine system you can only know that the energy pattern wold be similar due to the simetry, but not equal. If you want to calculate it exactly you must classically construct the whole field that all ligands create and start with parturbation theory calculus. This task colud be large with such complex ligands.

I´m sorry if this doesn´t help you. Good luck.
 
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1. What is pentacoordination of zinc?

Pentacoordination of zinc refers to the coordination of five ligands or molecules around a central zinc ion. This type of coordination is commonly found in zinc-containing enzymes and proteins, and plays a crucial role in their structure and function.

2. How is zinc able to form pentacoordinate complexes?

Zinc is able to form pentacoordinate complexes due to its electronic configuration. It has a d10 electronic configuration, which means it has four empty d orbitals that can be used for bonding with ligands.

3. What are the five most common ligands involved in pentacoordination of zinc?

The five most common ligands involved in pentacoordination of zinc are water, ammonia, chloride, hydroxide, and carboxylate. These ligands are able to form strong bonds with the zinc ion, resulting in stable pentacoordinate complexes.

4. What is the significance of pentacoordination of zinc in biological systems?

Pentacoordination of zinc plays a crucial role in biological systems, particularly in enzymes and proteins. It helps to stabilize the structure of these molecules, and also plays a role in their catalytic activity. This coordination also allows for specific interactions with other molecules, leading to important biological functions.

5. Are there any potential applications of pentacoordination of zinc in medicine?

Yes, there are potential applications of pentacoordination of zinc in medicine. Zinc-containing enzymes and proteins play important roles in various biological processes, and understanding their pentacoordination can aid in the development of new drugs and treatments for diseases. Additionally, zinc deficiency has been linked to various health issues, highlighting the importance of pentacoordination of zinc in maintaining overall health.

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