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Flashcards in Coordination Complexes Deck (51)
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What did Alfred Werner identify?

He identified principle features of geometric structures
He observed a violet and a green compound with the same formula CoCl3.4NH3
1 chloride in each compound reacts with Ag+ to form AgCl
He proposed the reactive chloride is not bound to cobalt
CoCl2(NH3)4 Cl-
He proposed the six bonded group are arranged in a symmetric fashion around the cobalt


What are the possible arrangements of the bonded groups around the cobalt - Werner

The arrangements include planar hexagon which has 3 isomers
Trigonal prismatic (2 isomers)
Octahedral (2 isomers)


Which arrangement did Werner conclude?

He only isolate two compounds (octahedral only has 2 isomers), violet and green
Likely arrangement of 6 ligands is octahedral
This is correct


What is a chiral compound?

This is a complex that is non superimposable on its mirror image and has no internal plane of symmetry


What is geometric isomerism

A complex can adopt two different geometries


Which geometries show isomerism?

Isomerism is possible in square planar complexes of the general formula MX2Y2 and when X and Y are different

Octahedral complexes MX4Y2 complexes exist as cis and trans geometric isomers


Which geometries do not show isomerism

Tetrahedral complexes of the general formula MX2Y2 do not form geometric isomers as there is only one way the four ligands can be arranged


Describe the cis and trans configuration of octahedral with formula MX4Y2

It is cis when the 2 Y atoms are adjacent
It is trans when the 2 Y atoms are adjacent

Cis is adjacent
Trans is opposite


What can octahedral complexes [MX3Y3] exist as?

They can exist can mer and fac
Mer is where 3 of the ligands X/Y in the same plane
Fac is where 3 ligands X/Y are adjacent (triangular face)


What confirmed werners predictions?

Optical isomerism confirmed Werners - octahedral

Optical activity is determining if a compound is chiral (optically active)


What does en mean?

en= ethane-1,2-diamine

The ligand binds using both N donor atoms
A curve can represent the CH2CH2 bridges in the en ligand


What does ^ and triangle mean?

Triangle= right rotation
^= left rotation


What is an enantiomer?

This is the mirror image of a chiral molecule

They are non superimposable


Why is chirality not important for coordination complexes?

This is because metal ligand bonds are labile
This means the ligands can break away and change places so the enantiomer undergoes racemisation


Why can bidentate ligand enantiomers be isolated where monodentate ligands cannot?

Mondentate ligand bonds are labile and so the enantiomers undergo rapid racemisation
Bidentate ligands are less labile so it is possible to isolate these enantiomers


What are bidentate isomers distinguished by and what do they form?

Bidentate ligands form a helix
The enantiomer forming the right handed, clockwise helix is labelled triangle
The left handed anti-clockwise helix is labelled ^


Why are trans complexes not chiral?

This is because they contain a mirror plane


How can you separate diastereoisomers?

They are separated by fractional distillation


How can you separate a racemic mixture of 2 enantiomers?

+ Ba d-tatrate
- BaSO4
And they are separated


What is geometric isomerism?

Geometric isomerism, also known as cis- trans isomerism or EZ isomerism is a form of stereoisomerism


Do enantiomers have the same properties?
Do diastereoisomers have the same properties?

Diastereoisomers have different properties
Enantiomers have the same properties apart from
-reactivity with chiral reagents
- reaction with plane polarised light


What is the most common coordination for d block complexes?

Six coordination is the most common for d block metals
The majority of 6 coordinate complexes are octahedral


What are some important distortions of octahedral complexes?

Stretching or compressing
1) a 4 fold rotation symmetry which results in tetragonal distortion

2) a 3 fold rotation symmetry axis results in trigonal distortion


Why are higher coordination numbers less common for 3d and more common for 4d and 5d?

The central metal atom is large and so can coordinate more than six ligands


What is geometry is most common for 7 coordinate complexes?

Pentagonal bipyramidal?


What is the most common geometry for 8 coordinate?

Square antiprismatic

Cubic geometry is possible but not observed due to greater ligand ligand repulsions


What geometry is common for 2 coordinate complexes?


It is common for ions with low charge density


What geometry is common for 3 coordinate complexes?

Trigonal planar but is rare


What geometry is common for 4 coordinate complexes?

Tetrahedral or square planar

Tetrachloro complexes can adopt either depending on the nature of the metal ion


When is tetrahedral favoured over square planar?

Tetrahedral is favoured when the central atom is small and the ligands are large