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Questions tagged [coordination-compounds]

This tag is for questions concerning coordination compounds including but not limited to ligand properties, metal properties, orbital splitting, micro- and macroscopic properties of entire complexes etc. For complexes where carbon monoxide is the only ligand, use the [carbonyl-complexes] tag instead. For organic catalysts or proteins, the tag is applicable if the question is about the metal’s direct coordination sphere.

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Why is it wrong to use the concept of hybridization for transition metal complexes?

I have asked a lot of questions on coordination chemistry here before and I have gone through a lot others here as well. Students, including me, attempt to answer those questions using the concept of ...
Arishta's user avatar
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69 votes
8 answers
75k views

Is iron in the brown ring compound in a +1 oxidation state?

In the standard brown ring test for the nitrate ion, the brown ring complex is: $$\ce{[Fe(H2O)5(NO)]^{2+}}$$ In this compound, the nitrosyl ligand is positively charged, and iron is in a $+1$ ...
ManishEarth's user avatar
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42 votes
6 answers
9k views

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? My question is not about ...
Anoneemus's user avatar
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41 votes
4 answers
134k views

Why does carbon monoxide have a greater affinity for hemoglobin than oxygen?

Hemoglobin is an iron-containing oxygen transport metalloprotein in the red blood cells of most mammals. Simply put, it's a carrier protein. Interestingly it doesn't carry carbon dioxide in the same ...
bonCodigo's user avatar
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38 votes
1 answer
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Why is [PdCl4]2- square planar whereas [NiCl4]2- is tetrahedral?

The molecule $\ce{[PdCl4]^2-}$ is diamagnetic, which indicates a square planar geometry as all eight d electrons are paired in the lower-energy orbitals. However, $\ce{[NiCl4]^2-}$ is also $\mathrm{d^...
user avatar
36 votes
4 answers
127k views

Tetrahedral or Square Planar

How can one predict whether a given complex ion will be square planar or tetrahedral when its coordination number is 4 using crystal field theory ? Is it possible to theoretically predict this?
Sameer's user avatar
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31 votes
1 answer
806 views

d-orbital splittings in WS2 monolayer

The formerly degenerate $d$ orbitals of the tungsten atoms in the $\ce{WS2}$ monolayer are split into three groups: (1) $\mathrm{d}_{z^2}$, (2) $\mathrm{d}_{x^2-y^2}, \mathrm{d}_{xy}$ and (3) $\mathrm{...
Capo Pavel Mestre's user avatar
28 votes
1 answer
104k views

What are t2g and eg in CFT?

In the crystal field theory (CFT), when the splitting of the d-orbital occurs, it gets divided into two parts. The upper part with higher energy is the $\mathrm{e_g}$ and the lower part with lower ...
NeilRoy's user avatar
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26 votes
3 answers
11k views

Solutions of Group 1 and Group 2 metals in Ammonia

When we add Group-1 and Group-2 metals to liquid ammonia, they dissolve to form metal cations and solvated electrons. $$\ce{M + NH3(liq) -> M+ + e-}$$ Now, when the G-1 solutions evaporate, we get ...
Ayushmaan's user avatar
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25 votes
4 answers
4k views

How may copper acetate ligands be manipulated to change colors?

I have a solution of copper acetate and I would like to play around with the ligands to get different colors. Background: The copper acetate was made through mixing vinegar (5% acetic acid), $\ce{...
Dale's user avatar
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25 votes
1 answer
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How can the intense color of potassium permanganate be explained with molecular orbital theory?

In the permanganate ion, manganese is in the $+7$ oxidation state, therefore it is a $\ce{d^0}$ ion. $\ce{d^0}$ and $\ce{d^1^0}$ ions don't absorb visible spectrum radiation because there are no ...
Nilay Ghosh's user avatar
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25 votes
1 answer
935 views

Why is Diiron nonacarbonyl so exceptional?

My textbook(NCERT) says: With exception of $\ce{Fe2(CO)9}$, all other metal carbonyls are soluble in hydrocarbon solvents. Weller, M.; Overton, T.; Rourke, J.; Armstrong, F. Inorganic Chemistry, ...
Nilay Ghosh's user avatar
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23 votes
2 answers
4k views

Why is the cyanide ion toxic?

As the title implies, what is the molecular basis of cyanide toxicity? I did some searching around at the CDC and it only states that it prevents cells from using oxygen. I also read how it could take ...
Aubrey Champagne's user avatar
22 votes
8 answers
14k views

Do ligands with a positive charge exist?

Are there positively charged ligands which can bind to a central metal atom to form coordination compounds? My thoughts: I know that ligands are Lewis bases which donate a pair of electrons, and the ...
Rajath Radhakrishnan's user avatar
22 votes
2 answers
9k views

Usage of ammine vs amine in nomenclature

In the nomenclature of complex salts we use ammine for NH3 instead of amine. I thought this was to differentiate between ammine ligand and amine in organic ligand (like en). However, Wikipedia ...
Freddy's user avatar
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21 votes
2 answers
6k views

What is the perfect definition for chirality?

Why is chirality defined differently for organic and inorganic compounds? Why are inorganic compounds deemed to be optically active if they have more than one of the same ligands attached to the ...
JM97's user avatar
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21 votes
5 answers
12k views

Why is the magnesium(II) ion preferred over other ions in chlorophyll?

Chlorophyll has a $\ce{Mg^2+}$ ion. Why is it preferred over other ions? For example, what happens if there is $\ce{Zn^2+}$ or $\ce{Ca^2+}$ or any other (divalent) cation instead of $\ce{Mg^2+}$?
adianadiadi's user avatar
21 votes
3 answers
12k views

Why is manganese(II) coloured although the transition should be spin-forbidden?

In every basic coordination chemistry class, at some early point the crystal field theory and LFSE will be taught, explaining that there will be an energy difference between d-orbitals (typically ...
Jan's user avatar
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21 votes
4 answers
10k views

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^+}\\ \ce{[Cu(OH)_2(H2O)...
Ivan's user avatar
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21 votes
1 answer
13k views

Why isn't the orbital angular momentum also considered while calculating the magnetic moments 3d transition elements?

My textbook (Chapter: The d- and f- Block Elements) makes an interesting assertion, however, without any reason to back it up. Paramagnetism arises from the presence of unpaired electons, each such ...
paracetamol's user avatar
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20 votes
3 answers
11k views

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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20 votes
1 answer
2k views

What causes the "Gd break" in the trend of lanthanide-EDTA formation constants?

Smith and Martell obtained a series of data for the binding of trivalent lanthanide ions, $\ce{Ln^3+}$, with various carboxylic acid ligands (amongst them the well-known EDTA).1 A graph of the ...
orthocresol's user avatar
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19 votes
1 answer
816 views

Why does benzene bend in this reaction?

From here I can see why hapticity changes here, but not why it is necessary for the benzene ring to bend. The resonance energy of benzene is pretty large, and there's no balancing increase in ...
ManishEarth's user avatar
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18 votes
3 answers
5k views

Where does the label ‘Dq’ to denote the field split in coordination compounds come from?

As established in a previous question, coordination compounds typically have a field split between the $\mathrm{t_{2g}}$ and the $\mathrm{e_g}$ d-orbitals.[1] This energy difference can be explained ...
Jan's user avatar
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18 votes
3 answers
47k views

Why is tetraamminecopper(II) a square planar and not a tetrahedral species?

In $\ce{[Cu(NH3)4]^2+}$, 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 going?
Dhruba Banerjee's user avatar
18 votes
3 answers
23k views

Hybridisation of Mn in potassium permanganate

I'm clear with the concepts of crystal field theory. But I can't figure out the exact reason why the hybridisation of manganese in potassium permanganate ($\ce{KMnO4}$) is $\mathrm{d^3s}$. Can anyone ...
Devgeet Patel's user avatar
18 votes
2 answers
53k views

In Crystal Field Theory what does Δo=10Dq mean?

While studying the Crystal Field Theory I was told $\mathrm{Dq}$ is a unit, related to the unit $\Delta_{\mathrm{O}}$ by the relation $\Delta_{\mathrm{O}} = 10\ \mathrm{Dq}$. But aren't $\Delta_{\...
Charles's user avatar
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17 votes
2 answers
4k views

What happens to electrons in metal complexes after excitation by visible light?

My book writes: When white light shines through a solution of a complex ion of a transition metal, photons of a particular frequency are absorbed and their energy promotes an electron from lower ...
Eliza's user avatar
  • 2,413
17 votes
3 answers
5k views

Disproportionation of Au(II)

$\ce{Cu(II)}$ and $\ce{Ag(II)}$ complexes are known to exist while $\ce{Au(II)}$ is unstable and disproportionates to $\ce{Au(I)}$ and $\ce{Au(III)}$. My guess as to possible reasons to this effect ...
Maan's user avatar
  • 291
16 votes
3 answers
8k views

Why is anhydrous copper(II) sulfate white while the pentahydrate is blue, even though both have one unpaired electron?

We all know that $\ce{CuSO4.5H2O}$ is blue and it turns to $\ce{CuSO4}$ on heating which is white. I also learnt about coordination complexes and d–d transitions and how transition metal compounds are ...
Kartik's user avatar
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16 votes
1 answer
7k views

Splitting of $d$ orbitals when ligands approach central metal ion

In my high school chemistry book, it is written that when ligands approach the central metal ion (transition metal ion) to form dative bonds, the $3d$ orbitals split into two: two which are in higher ...
Eliza's user avatar
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16 votes
1 answer
54k views

What is the product of the chemical reaction between phenol and ferric chloride?

The chemical reaction between phenol and ferric chloride is a test for the presence of phenol. They react with each other to produce a violet complex. However, the reaction is given differently in ...
Nilay Ghosh's user avatar
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16 votes
2 answers
341 views

What are the mechanisms for capture of As(III) and As(V) by magnetite from water?

Magnetite, $\ce{Fe3O4}$ is able to capture $\ce{As(III)}$ and $\ce{As(V)}$ from drinking water through the following mechanisms. Bidentate-binuclear complex Monodentate-binuclear complex (both from ...
jonsca's user avatar
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16 votes
1 answer
800 views

IUPAC name of C₆(CH₃)₆²⁺

What is the correct IUPAC name (or least incorrect one, if the current rules can't precisely describe that) of the interesting species $\ce{[C6(CH3)6]^{2+}}$ (which is extensively discussed here), ...
mykhal's user avatar
  • 6,212
15 votes
2 answers
1k views

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 ...
docscience's user avatar
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15 votes
3 answers
17k views

What is the reason of the color difference for the cis/trans isomers of tetraamminedichloridocobalt(III) chloride?

The cis and trans isomers of $\ce{[CoCl2(NH3)4]Cl}$ are quite famous as one is purple and the other one is green which is a huge difference in color. Now I can't find any information to why this is ...
Justanotherchemist's user avatar
15 votes
1 answer
5k views

The bond in coordination complexes

This is a very basic question and I'm surprised it only just struck me. The nature of the bond in coordination complexes is a coordinate covalent bond. Only the ligand donates electrons for bond ...
Keerthana A.K.'s user avatar
15 votes
1 answer
5k views

What does the eta notation mean in the naming of a transition metal complex?

I am reading a paper (Gutel et al., J. Mater. Chem. 2007, 17, 3290-3292) and I have come across the following reaction: In organic solvents, the decomposition under mild conditions of ($\eta^4$-1,...
Andrew's user avatar
  • 1,043
14 votes
3 answers
14k views

Can Fe(CO)5 adopt both square pyramidal and trigonal bipyramidal geometries?

I know the hybridization of $\ce{Fe(CO)5}$ is $\mathrm{dsp^3}$. According to my book, coordination compounds with coordination number 5 can interchange between square pyramidal and trigonal ...
user avatar
14 votes
1 answer
4k views

Molecular orbital diagram of a complex including an oxido ligand

With highly oxidized metal centers, we expect that the hydroxido ligand's proton becomes acidic and will be lost to the surrounding media, creating an oxido ligand. The oxo ligand is a $\pi$ basic ...
RedPen's user avatar
  • 963
13 votes
5 answers
9k views

Explanation for why nickel turns green in hydrochloric acid

My daughter has a chemistry test that I am helping her prepare for. One question is Nickel sulfate, $\ce{NiSO4(aq)}$ is a green solution. Nickel chloride, $\ce{NiCl2(aq)},$ is a yellow solution. If ...
jsd's user avatar
  • 241
13 votes
1 answer
3k views

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 ...
bon's user avatar
  • 15.4k
13 votes
2 answers
509 views

Is aqueous medium necessary for complex formation? if so, why?

If dry ammonia gas is passed through anhydrous copper sulfate, will it turn blue (due to the formation of tetraamminecopper(II) complex)? Or will silver chloride form diamminesilver(I) complex in ...
Megha's user avatar
  • 141
13 votes
2 answers
12k views

Why do octahedral metal ligand complexes have greater splitting than tetrahedral complexes?

Octahedral complexes have greater splitting in the d orbitals. Is it because octahedral complexes have more atoms and thus more interactions?
CognisMantis's user avatar
  • 1,648
13 votes
1 answer
4k views

The IUPAC name of sodium nitroprusside, and back-bonding in it

In the standard test for the sulfide ion, sodium nitroprusside $(\ce{Na^_2[Fe(CN)5(NO)]})$ is used. The IUPAC name for this compound as stated by Wikipedia is sodium pentacyanidonitrosylferrate(II) I ...
miyagi_do's user avatar
  • 2,044
13 votes
1 answer
34k views

Why are d-d electronic transitions forbidden and weakly absorbing? Why do they occur at all?

I am unable to understand why d-d electronic transitions are forbidden? Why are they weakly absorbing and apart from that, why do they occur at all?
Saroj's user avatar
  • 562
13 votes
1 answer
10k views

Why is (NH4)2[CuCl4] square planar complex but Cs2[CuCl4] is tetrahedral?

Why is $\ce{(NH4)2[CuCl4]}$ square planar complex but $\ce{Cs2[CuCl4]}$ is tetrahedral even though both have same oxidation number of copper and same ligands?
user avatar
13 votes
1 answer
4k views

IS DMSO-o a σ-donor, a π-donor, or both?

DMSO is an ambidentate ligand that can bind in a κO fashion via the oxygen lone pair and in a κS fashion via the sulfur lone pair. I know that DMSO can behave as a π-acceptor when it ...
gannex's user avatar
  • 2,334
13 votes
3 answers
514 views

Comparison of C=O bond strength in metal carbonyls

Find the weakest $\ce{C=O}$ bond among $\ce{[Mn(CO)6]+},$ $\ce{Fe[(CO)5]},$ $\ce{[Cr(CO)6]}$ and $\ce{[V(CO)6]-}.$ I thought the $\ce{C=O}$ bond strength would be lowest in $\ce{[V(CO)6]-}$ since the ...
m-Xylene's user avatar
  • 577
12 votes
4 answers
6k views

Are complex ions thermochromic?

Does raising the temperature of a complex ion (formed from a transition metal ion and ligand(s)) affect its color? For example, if the temperature of $\ce{[Cr(H2O)6]^3+}$ is raised, will its color ...
sepehr78's user avatar
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