77
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Why is it wrong to use the concept of hybridization for transition metal complexes?
Tetrahedral complexes
Let's consider, for example, a tetrahedral $\ce{Ni(II)}$ complex ($\mathrm{d^8}$), like $\ce{[NiCl4]^2-}$. According to hybridisation theory, the central nickel ion has $\mathrm{...
- 71.1k
42
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Why is [PdCl4]2- square planar whereas [NiCl4]2- is tetrahedral?
The geometry of the complex changes going from $\ce{[NiCl4]^2-}$ to $\ce{[PdCl4]^2-}$. Clearly this cannot be due to any change in the ligand since it is the same in both cases. It is the other factor,...
- 71.1k
31
votes
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What is the perfect definition for chirality?
The correct definition of chirality is given in the IUPAC gold book as follows:
chirality
The geometric property of a rigid object (or spatial arrangement of points or atoms) of being non-...
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27
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Why is the cyanide ion toxic?
Cyanide is a pretty good ligand for coordination compounds. The electron pair on carbon (which, incidentally, also carries the Lewis structure’s formal charge) is located in the HOMO — much like as in ...
- 67.3k
27
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What is the perfect definition for chirality?
I think Martin has provided an excellent answer, and I would like to supplement it with a few additional details and examples that might prove insightful.
So as I already mentioned in the comments, ...
- 8,465
26
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Why does carbon monoxide have a greater affinity for hemoglobin than oxygen?
Excursion into simple coordination chemistry: Bonding, backbonding and simple orbital schemes
Please refer to Breaking Bioinformatic’s answer for the MO scheme of carbon monoxide, it is very helpful. ...
- 67.3k
23
votes
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Why is manganese(II) coloured although the transition should be spin-forbidden?
Selection rules
The intensity of the transition from a state $\mathrm{i}$ to a state $\mathrm{f}$ is governed by the transition dipole moment $\mu_{\mathrm{fi}}$ (strictly, it is proportional to $|\...
- 71.1k
22
votes
Why isn't the orbital angular momentum also considered while calculating the magnetic moments 3d transition elements?
Simplistically speaking orbital angular momentum is present when some conditions are satisfied:
A set of orbitals are degenerate;
These orbitals can be "interconverted" by rotation about a certain ...
- 71.1k
21
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Is there a mnemonic to study the spectrochemical series?
I would not recommend a mnemonic for the spectrochemical series for a number of reasons:
Often, it depends on both metal and ligand and coordination geometry how big a certain splitting is.
The ...
- 67.3k
21
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Explanation for why nickel turns green in hydrochloric acid
The question is really badly worded. For starters, let’s look at solutions of nickel(II):
Figure 1: Nickel(II) solutions. From left to right: $\ce{[Ni(NH3)6]^2+}$, $\ce{[Ni(en)3]^2+}$, $\ce{[NiCl4]^2-...
- 67.3k
19
votes
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Oxalate ion dentiticity - why is it bidentate and not tetradentate?
The oxalate anion cannot be tetradentate. While there are four oxygen atoms, the ion is planar and the oxygen atoms are pointing in different directions.
The best any metal can do is bond to two of ...
- 42.6k
19
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How can the intense color of potassium permanganate be explained with molecular orbital theory?
Let’s take a look at a qualitative MO scheme for a tetrahedric transition metal complex whose ligands have three p-type orbitals each. On the left of figure 1 you have the metal orbitals ($\mathrm{3d}$...
- 67.3k
19
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Can Fe(CO)5 adopt both square pyramidal and trigonal bipyramidal geometries?
Your book was correct that a five coordinate metal complex is able to adopt both square pyramidal and trigonal bipyramidal geometries, and in both cases the sp3d hybridisation scheme applies (if you ...
- 17.1k
19
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Where does the label ‘Dq’ to denote the field split in coordination compounds come from?
I will expand my previous comment into an answer.
In the $O_h$ case the metal ion is surrounded by $6$ ligand ions, each with charge $q=-Ze$ located at $\langle\pm a,0,0\rangle$, $\langle0, \pm a,0\...
- 1,058
18
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Why are low spin tetrahedral complexes so rare?
Hybridisation won't explain anything in transition metal complexes, so please stop using it, at least to the extent where it is possible to avoid using it. Quite literally everything about transition ...
- 71.1k
17
votes
Usage of ammine vs amine in nomenclature
(Will do more research into ammines come February.)
Premise
Ammonia is spelled with two 'm's. The more natural derivative of the word in a linguistic sense would also have the same number 'm's. Thus ...
- 7,021
17
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How to name Hg[Co(SCN)4]?
TL;DR: There is no inner- or outer coordination spheres in this complex. Both cobalt(II) and mercury(II) have nearly ideal tetrahedral coordination environment with $4$ $\ce{N}$ and $4$ $\ce{S}$ atoms,...
- 37.4k
16
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Why is anhydrous copper(II) sulfate white while the pentahydrate is blue, even though both have one unpaired electron?
Let's compare the two compounds, here I plotted the $\ce{Cu(II)}$ centers of $\ce{CuSO4.5H2O}$ and $\ce{CuSO4}$ from their crystal structure data.
As you can see, it changes from a $\ce{[Cu(H2O)4[SO4]...
- 4,232
16
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Why is Ni[(PPh₃)₂Cl₂] tetrahedral?
We sometimes call this type of complex 'pseudotetrahedral' since there is an isomerism from a tetrahedral to a square planar complex possible. I was unable to find the original work here but this link ...
- 4,232
15
votes
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How can the hybridisation schemes of transition metal complexes be determined?
Firstly, note that hybridisation theory as applied to transition metal complexes is an incorrect, flawed theory. It is an attempt to rationalise experimental observation (e.g. geometries), but in the ...
- 71.1k
15
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How can AuCl3 exist?
Gold(III) chloride does not exist as $\ce{AuCl3}$. According to Wikipedia, the name gold trichloride is a simplification of the name, which is referring to the empirical formula, $\ce{AuCl3}$. The X-...
- 39.5k
14
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Can an atom bond with more than 8 other atoms?
In october 2015, 5 months after all the current answers were given, a new cluster compound witn C.N. 16, $\ce{CoB16-}$, has been reported [1]:
Here we report the observation of a large metal-doped ...
- 37.4k
14
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18 Electron Rule For Determining the Stability of Transition Metal Complexes
A brief description of the 18 electron rule
A valence shell of a transition metal contains the following: 1 $s$ orbital, 3 $p$ orbitals and 5 $d$ orbitals; 9 orbitals that can collectively ...
- 8,465
14
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Where does the label ‘Dq’ to denote the field split in coordination compounds come from?
I currently happen to have the book by Figgis that Max mentioned. Chapter 2 is devoted to a mathematical formulation of crystal field theory, which I did not bother reading in detail because I do not ...
- 71.1k
14
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How does Potassium Hexfluoronickelate(IV) exist in a stable state?
To quote from the comments: you can get things into an amazing variety of oxidation state given the right environment.
In the case of maximal oxidation states, particularly above $+2$ or $+3$ in the $...
- 53.2k
13
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The IUPAC name of sodium nitroprusside, and back-bonding in it
Nitrosyl is the textbook example for a non-innocent ligand — that is, one that can appear in different oxidation states with different numbers of donated electrons and can make determining the bonding ...
- 67.3k
13
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Metal carbonyl bonding
Carbon monoxide bonds to transition metals using "synergistic π* back-bonding." The bonding has three components, giving rise to a partial triple bond. A sigma bond arises from overlap of the ...
- 341
13
votes
Why is the magnesium(II) ion preferred over other ions in chlorophyll?
Chlorophyll in plants has two main functions. First, it facilitates energy transfer of an absorbed photon's energy via the many other chlorophylls that constitute the antenna pigment-protein complex ...
- 30k
13
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Where does the label ‘Dq’ to denote the field split in coordination compounds come from?
A more high-level answer this time. In this approach we first find out the form of the term in the potential that will split the $d$ orbitals.
Recall that the character of a proper rotation by angle $\...
- 1,058
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