A special class of compounds in which a electron deficient central atom (usually a metal ion) is bonded to many electron donors called ligands. These compounds are highly stable and are widely found in nature. They also have a wide variety of industrial applications.

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Tollen's Test and Werner's Theory

The production of silver ions in Tollen's test violates Werner's theory of non - ionizable secondary valency since we are using the diamminesilver(I) complex as the reagent. How does one reason ...
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Why don't electrons pair in [Fe(NH3)6]2+?

Why doesn't electron pairing take place in $\ce{[Fe(NH3)6]^2+}$ though $\ce{NH3}$ is a strong ligand field producer?
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Name the following coordination complex

What are the IUPAC rules when naming a coordination complex like: $$\ce{[Pt(NH3)4][Pt(NH3)Cl3]}$$ Now according to my textbook, it is named as tetraammineplatinum(II) ...
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metal ligand complex stabilities [closed]

Among the metal ligand forming a complex,which one has higher stability constant? Ni(2+) and Sr(2+) are the metal ions. The ligands are as follows:- 1-amino-2-thiolethane and 2-aminoaceticacid
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Preparation of Mg-EDTA for titrations

I need to prepare such a solution for a titration by EDTA displacement, but nearly every source I find only mentions it by referencing the method, not by listing the prepare of the solution itself. ...
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Can high-spin complex be diamagnetic?

There are two nickel complexes: one is of octahedral and the other of square planar shape. One complex is diamagnetic, the other is paramagnetic. Both are high-spin. Now, $\ce{Ni^2+}$ that is ...
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Why do ligands have such a small effect on overall absorption of a complexed ion?

When a metal cation is complexed, there is strong UV-Vis absorption due to the splitting of its $d$ orbitals, thereby allowing electronic transitions. My understanding is that ligands contribute very ...
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Why [Cu(NH3)4]^2+ is a square planar species and not a tetrahedral species?

In the above-mentioned species, the $\ce{Cu^2+}$ ion has 9 electrons in the $\mathrm{3d}$ orbital with only one unpaired electron. How is it a square planar geometry? Where is that unpaired electron ...
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Why carbon monoxide has a greater affinity for Hemoglobin compared to oxygen?

Hemoglobin is an iron-containing oxygen transport metalloprotein in the red blood cells of most mammalians. Simply put it's a carrier protein. Interestingly it doesn't carry carbon dioxide the same ...
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What is that process called in which we add water molecules to an ion to form a complex?

An example would be $\ce{[Fe(H2O)6]^2+}$ in which it has 6 water molecules associated with it. What is the process of adding these water molecules called?
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Trans effect on square planar complex

We've learnt about the trans effect but I have a question regarding how this plays a role with water in the equation. trans-effect: $$\ce{H2O < NH3 < Cl2}$$ Based on this, given ...
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Identifying Alkyl Ligands as Pi Donors or Pi Acceptors in Transition Metal Complexes

Just wondering if there was a systematic way to identify an alkyl ligand as a $\pi$ acceptor or $\pi$ donor in a transition metal complex? Although various sources indicate that weak field ligands ...
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Are all complexes with a polydentate ligand examples of chelation?

I'm getting a little confused about the definition of chelation and its implications (I should probably point out I'm only an A2 Chemistry student). The IUPAC defines chelation as the following: ...
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Why are compounds of V5+ and Cr6+ colored?

As far as my knowledge goes, transition metal complex ions show a color due to a transfer of electrons between the levels of split $d$-orbitals. In the case of $\ce{V^{5+}}$ and $\ce{Cr^{6+}}$ ...
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Why doesn't EDTA complex with alkali metal ions?

EDTA complexes with all the other metal ions in the periodic table except those from the group 1. Why is this so ? What is the coordination chemistry behind this ?
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Can an atom bond with more than 8 other atoms?

Is it possible for an atom to bond with 8 other elements (same or other type)? If yes, then please give some examples. If no, then what could be the possible reason for it? Update + Edit: My question ...
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Why does the value of Δo increase with increased charge on the metal?

A greater positive charge means the ligand is strongly attracted and pulled closer, and thus it creates a stronger crystal field. The potential energy value of the barycentre should thus be higher, ...
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Water exchange at Al (III)

Why is the rate of water exchange at Al(III) centres so slow ? According to this medical book (p.5) it is $10^{5}$ times faster at Mg(II).
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Methyl orange coordination compound chemistry

Methyl orange changes colors depending on the acidity or basicity of the solution. But I have read that it forms complexes with certain ions. Can anybody suggest any resource regarding the ...
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Nomenclature of complexes: Cyano vs Cyanido ; Chloro vs Chlorido

What is the correct nomenclature for $\ce{CN^-}$ and $\ce{Cl^-}$ ligands in coordination compounds? Wikipedia says the coding name(?) as cyanido and chlorido while this suggests cyano and chloro. ...
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Crystal field theory for calculating lattice parameters

If I have an 8-coordinated metal cation (e.g., $\ce{Te}$, $\ce{Nb}$, $\ce{Ta}$, $\ce{Sb}$, $\ce{Bi}$, $\ce{Zr}$, $\ce{Hf}$) by oxygen anions, is there a way to theoretically calculate the structure of ...
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In Crystal Field Theory what does Δo=10Dq mean?

While studying the Crystal Field Theory I was told $D_q$ is a unit, related to the unit $\Delta_{\mathrm{O}}$ by the relation $\Delta_{\mathrm{O}} = 10 D_q$. But aren't $\Delta_{\mathrm{O}}$ and $D_q$ ...
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What's so special about chelation? [duplicate]

There is another closely related post here , and I've also read the referenced wiki article including applications of chelation, but I still don't see what's so special about chelation. I understand ...
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Reaction between [Cu(NH3)6]2+ and NaOH [closed]

What type of reaction occurs between $\ce{[Cu(NH_3)_6]^{2+}}$ and $\ce{NaOH}$ and what are the products. And what happens when $\ce{NH_3}$ is evaporated from the product? can someone explain please.
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Determining spin of metal complex

Is there any way to determine the spin of $\ce{[Fe(OH)6]^{4-}}$ without looking at the spectrochemical series?
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Purpose of ammine in Tollens' reagent

In this previous question the mechanism for the reaction of Tollens' reagent was outlined. As I understand it the oxidising agent in Tollens' is the diamminesilver(I) complex $\ce{[Ag(NH3)2]+}$ but ...
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why is cobalt hexacyano complex uncommon?

In huheey they have written hexacyano cobalt(II) is uncommon but pentacyanoaqua cobalt (II) is common. They mentioned something about Jahn Teller distortion but I could not get the meaning
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High or low spin complex of Zn2+ and Ti3+

The zinc ion in its +2 state can show no more pairing, since all the electrons are already paired - so in any complex it forms it will have the same magnetic moment as it does right now. $\ce{Ti}$ in ...
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Why is ligand substitution only partial with copper(II) ions and ammonia?

When studying ligand substitution (at UK year 13 level), the following example has been given: \begin{align} \ce{[Cu(H2O)_6]^2+ + 2NH3 &<=> [Cu(OH)_2(H2O)_6] + 2NH4^+}\\ ...
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Oxo ligand molecular orbital diagram with metal center

With highly oxidizing metal center, we expect that the hydroxide ligand's proton becomes acidic and will be lost to the surrounding media, creating an oxo ligand. The oxo ligand is a $\pi$ basic ...
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Is hydrolytic polymerisation the mechanism by which the precipitate forms from the neutral complex?

From basic coordination chemistry and acid-base equilibria we understand that a metal hexa-aqua ion can be deprotonated until it's positive charge is balanced by the negative charge of the hydroxides ...
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Calculation of CFSE

I need to find CFSE for these: $\ce{[Ti(H2O)6]^3+}$, OK $\rm Ti$ is $\rm 4s^23d^2$, $\rm Ti^{3+}$ is $\rm 4s^03d^1$. Afterwards it becomes $\rm d^4sp^2$ or $\rm t_{2g}^5e_g^4$ so CFSE is ...
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Reaction with silver oxalate?

I was asked which geometrical isomer of $\ce{[M(NH3)2Cl2]}$, viz. cis or trans would react with silver oxalate. The possible reaction could be formation of silver chloride but since the coordination ...
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Rate constants for water exchange

Are rate constants for water exchange of transition metal aqua-complexes tabulated anywhere ? I haven't been able to find a resource which is anywhere near comprehensive.
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Why [MnCl6]^2- has got 4 unpaired electrons instead of 3?

In $\ce{[MnCl_6]}^{2-}$, $\ce{Mn}$ has +4 oxidation state which gives it a $\ce{3d^3}$ $\ce{4s^0}$ configuration. But how is it having 4 unpaired electrons?
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Why do charges result on atoms when coordinate bonds are formed?

I have not been able to get my head around it yet. For instance in the reaction between ammonia and borontrifloride why is it that a positive and a negative charge results? Is it that ammonia ...
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Can any atom donate more than 1 lone pair as a coordinate bond to the same metal?

This would mean the formation of a sigma and one or two pi bonds, all coordinate. I haven't heard of this happening, like fluorine anion or water with 2 lone pairs on O will donate only one lone pair, ...
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How hydrate isomerism results difference in colours?

The standard example is $\ce{CrCl3.6H2O}$, which can have three distinctly different crystalline compounds now known as $\ce{[Cr(H2O)6]Cl3}$ (violet), $\ce{[CrCl(H2O)5]Cl .H2O}$ (blue-green), and ...
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What is the highest possible expanded octet?

Often called "hypervalent", chemicals like Phosphorous Pentachloride and Sulfur Hexaflouride are possible due to the fact that their central atoms form covalent bonds with more than four other atoms, ...
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Decomposition of hexaurea-chromic-chloride-trihydrate

I am sitting over a TG diagram of the decomposition steps of hexaurea-chromic-chloride-trihydrate ($\ce{[Cr(CO(NH2)2)6]Cl3 \cdot 3 H2O}$) and cannot really make sense of the products it might ...
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Changing solubility of metal complex by adding ethanol

After creating a solution of copper(II)-sulfate-pentahydrate, water and concentrated ammonia, the newly formed complex (tetraamminecopper(II)-sulfate-monohydrate) is completely dissolved in water. By ...
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Why Bari centre is considered as Zero energy level?

Why the degenerate energy level of d orbitals before forming complex is considered zero? what advantages are there for taking the mean of t2g and eg orbitals as zero?
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Does sodium form complexes like transition metal ions?

I realise that there is a similar question here Difference between sodium ion and a transition metal ion dissolving in water? and it seems to answer my question, however I was reading about how ...
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Iodine color change in different complexes

Why does the color of iodine differ when it forms a charge transfer complex with benzene (pi donor) - pink and ethanol (electron pair donor) - brown? Does the HOMO-LUMO energy differ, if so how?
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Why member ring is favoured in chelates?

why chelates which form 3 or 4 member rings or 6 or 7 member rings are as stable as 5 member ring chelates? for example if we measure stability of chelates with oxygen donors, say oxalate, malonate, ...
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what are possible isomers of (meso-stilbenediamine)(isobutylenediamine) palladium (II)?

It can form a square planar and a tetrahedral complex but within square planar or within tetrahedral can there be isomers possible?
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Does tetramine copper dissolve cellulose?

I saw a Youtube video which showed that cotton (cellulose) dissolves in deep blue solution of tetramine copper made by adding 20% ammonia in copper carbonate salt. I tried to replicate the process ...
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Why should a complexometric titration be kept neutral?

In my next lab, I'll be doing a complexometric titration of a copper solution with EDTA and a murexide indicator. The lab guide advises to keep the pH level nearly neutral by adding a diluted ...
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Ratio of copper(II) ions to EDTA?

One question in a test I am preparing for is: What is the ratio of copper(II) ions to EDTA in a $\ce{[Cu(EDTA)]^{2-}}$ complex? I know that EDTA forms up to 6 coordinate bonds with the central ...