complex ions - shapes (2022)

THE SHAPES OF COMPLEX METAL IONS

This page describes the shapes of some common complex metal ions. It goes on to look at some simple examples of stereoisomerism (geometric and optical) in complex ions. If you aren't sure what stereoisomerism is, you will find a helpful link further down the page.

Some simple shapes for complex ions

These shapes are for complex ions formed using monodentate ligands - ligands which only form one bond to the central metal ion.

You will probably be familiar with working out the shapes of simple compounds using the electron pair repulsion theory. Unfortunately that doesn't work for most complex metal ions involving transition metals. The answer is just to learn the shapes you need to know about. As you will see, it isn't difficult.

Note: If you are interested (although it is completely irrelevant to this page), you will find an explanation of how you work out the shapes of simple molecules and ions by following this link.

You don't need to know about this to understand the rest of this page!


6-co-ordinated complex ions

These are complex ions in which the central metal ion is forming six bonds. In the simple cases we are talking about, that means that it will be attached to six ligands.

These ions have an octahedral shape. Four of the ligands are in one plane, with the fifth one above the plane, and the sixth one below the plane.

The diagram shows four fairly random examples of octahedral ions.

complex ions - shapes (1)

(Video) Shapes of Complex Ions | A-level Chemistry | OCR, AQA, Edexcel

Note: Remember that the ligands attached to a wedge shaped arrow are coming out of the screen or paper towards you. Those attached to a dotted arrow are behind the plane of the screen or paper. The two ligands attached to the ordinary arrows are above and below the plane of the rest.

It doesn't matter what the ligands are. If you have six of them, this is the shape they will take up. Easy!

4-co-ordinated complex ions

These are far less common, and they can take up one of two different shapes.

Tetrahedral ions

These are the ones you are most likely to need for A' level purposes in the UK. There are two very similar ions which crop up commonly at this level: [CuCl4]2- and [CoCl4]2-.

The copper(II) and cobalt(II) ions have four chloride ions bonded to them rather than six, because the chloride ions are too big to fit any more around the central metal ion.

complex ions - shapes (2)

That's not very difficult to remember either!

A square planar complex

Occasionally a 4-co-ordinated complex turns out to be square planar. There's no easy way of predicting that this is going to happen. The only one you might possibly come across at this level is cisplatin which is used as an anti-cancer drug.

Cisplatin is a neutral complex, Pt(NH3)2Cl2. It is neutral because the 2+ charge of the original platinum(II) ion is exactly cancelled by the two negative charges supplied by the chloride ions.

(Video) Shapes of complex Ions, Paper 1 - AQA A Level Chemistry

complex ions - shapes (3)

The platinum, the two chlorines, and the two nitrogens are all in the same plane. We will have more to say about cisplatin immediately below.

Stereoisomerism in complex ions

Some complex ions can show either optical or geometric isomerism.

Warning! If you don't know about optical and geometric isomers, it is essential that you explore the isomerism menu in the organic chemistry section of this site before you go any further. The rest of this page is unlikely to mean anything to you if you don't have this background!

Use the BACK button, or the History file, or the Go menu on your browser to return to this page - depending on how waylaid you get!


Geometric isomerism

This occurs in planar complexes like the Pt(NH3)2Cl2 we've just looked at. There are two completely different ways in which the ammonias and chloride ions could arrange themselves around the central platinum ion:

complex ions - shapes (4)

The two structures drawn are isomers because there is no way that you can just twist one to turn it into the other. The complexes are both locked into their current forms.

The terms cis and trans are used in the same way as they are in organic chemistry. Trans implies "opposite" - notice that the ammonias are arranged opposite each other in that version, and so are the chlorines. Cis implies "on the same side" - in this instance, that just means that the ammonias and the chlorines are next door to each other.

Optical isomerism

(Video) Shapes of complex ions from www.ChemistryTuition.Net

You recognise optical isomers because they have no plane of symmetry. In the organic case, it is fairly easy to recognise the possibiliy of this by looking for a carbon atom with four different things attached to it. It isn't quite so easy with the complex ions - either to draw or to visualise!

The examples you are most likely to need occur in octahedral complexes which contain bidentate ligands - ions like [Ni(NH2CH2CH2NH2)3]2+ or [Cr(C2O4)3]3-.

Help! If these ions look scarily unfamiliar, you must read the introductory page on complex ions before you go on. The shapes of the ions given below will be simplified in a way that is explained on that page.

Use the BACK button on your browser to return to this page.


The diagram below shows a simplified view of one of these ions. Essentially, they all have the same shape - all that differs is the nature of the "headphones".

I have deliberately left the charges off the ion, because obviously they will vary from case to case. The shape shown applies to any ion of this kind.

complex ions - shapes (5)

If your visual imagination will cope, you may be able to see that this ion has no plane of symmetry. If you find this difficult to visualise, the only solution is to make the ion out of a lump of plasticene (or a bit of clay or dough) and three bits of cardboard cut to shape.

A substance with no plane of symmetry is going to have optical isomers - one of which is the mirror image of the other. One of the isomers will rotate the plane of polarisation of plane polarised light clockwise; the other rotates it anti-clockwise.

Help! If you don't understand what I am talking about, it is because you didn't take my advice and follow the link to the isomerism part of the site earlier on this page! You need to read about optical isomerism in the organic chemistry section of this site.

Use the BACK button on your browser to return to this page .


In this case, the two isomers are:

complex ions - shapes (6)

(Video) Complex Ions and Their Ligands | A-level Chemistry | OCR, AQA, Edexcel

If you have a really impressive visual imagination, you may be able to see that there is no way of rotating the second isomer in space so that it looks exactly the same as the first one. I can't do this! The only way I have ever been able to convince myself that they are different is to make models.

For exam purposes, this doesn't matter in the slightest. As long as you draw the isomers carefully, with the second one a true reflection of the first, the two structures will be different.

Questions to test your understanding

If this is the first set of questions you have done, please read the introductory page before you start. You will need to use the BACK BUTTON on your browser to come back here afterwards.

questions on the shapes of complexes

answers

Where would you like to go now?

To the complex ion menu . . .

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(Video) Complex Ions, Ligands, & Coordination Compounds, Basic Introduction Chemistry

© Jim Clark 2003 (modified November 2014)

FAQs

What is the shape of complex ion? ›

Common complex shapes of metal ions

Linear. Square planar. Tetrahedral. Octahedral.

What forms complex ions? ›

A complex ion forms from a metal ion and a ligand because of a Lewis acid–base interaction. The positively charged metal ion acts as a Lewis acid, and the ligand, with one or more lone pairs of electrons, acts as a Lewis base.

How do you know if a complex is tetrahedral or square planar? ›

A square planar complex also has a coordination number of 4. The structure of the complex differs from tetrahedral because the ligands form a simple square on the x and y axes. Because of this, the crystal field splitting is also different (Figure 1).

How do you know if a complex is octahedral or tetrahedral? ›

When two or more types of ligands are coordinated to an octahedral metal center, the complex can exist as isomers. The number of possible isomers can reach 30 for an octahedral complex with six different ligands (in contrast, only two stereoisomers are possible for a tetrahedral complex with four different ligands).

What are tetrahedral complexes? ›

Tetrahedral complexes are formed with late transition metal ions (Co2+, Cu2+, Zn2+, Cd2+) and some early transition metals (Ti4+, Mn2+), especially in situations where the ligands are large. In these cases the small metal ion cannot easily accommodate a coordination number higher than four.

Which of the following complex ion is tetrahedral? ›

The [CoCl4]2- complex ion is experimentally known to have a tetrahedral structure.

What is the shape of nh4? ›

Q. Specify the geometry and the hybridisation of N and B atoms in a 1:1 complex of BF3 and NH3.

Which of the following complex ion is tetrahedral in nature? ›

There are 4 CN− ions. Thus, it can either have a tetrahedral geometry or square planar geometry. Since CN− ion is a strong field ligand, it causes the pairing of unpaired 3d electrons.

What is a complex ion example? ›

They are a type of coordination complex. The central ion is the coordination center, while the molecules or ions bound to it are termed complexing agents or ligands. Examples: The copper ammine ion, Cu(NH3)62+ is a complex ion.

How do you name complex ions? ›

In naming the complex ion:
  1. Name the ligands first, in alphabetical order, then the metal atom or ion. ...
  2. The names of some common ligands are listed in Table 1. ...
  3. Greek prefixes are used to designate the number of each type of ligand in the complex ion, e.g. di-, tri- and tetra-.

Why are complex ions Coloured? ›

As the oxidation state of the metal increases, so also does the amount of splitting of the d orbitals. Changes of oxidation state therefore change the colour of the light absorbed, and so the colour of the light you see.

Which complex has square planar structure? ›

Solution : `[Ni(CN)_(4)]^(2-)`has square planar structure Hence, (C) is the correct answer.

Why are platinum complexes square planar? ›

A strong repulsion with the electron and ligand take place in between the platinum which leads to a strong crystal field splitting. Thus, the splitting breaks the degeneracy of dx2-y2 and dz2. This degeneracy stabilizes more to the square planar arrangement than the tetrahedral.

Is octahedral and square planar same? ›

From what I understand, Square Planar has an atom in the middle of the other atoms that form the corners of the square while octahedral doesn't.

What is EG and t2g? ›

In the presence asymmetrical field, splitting of the d orbitals takes place. The pattern of splitting depends upon the nature of the crystal field. The dxy, dxz, and dyz orbitals are collectively called the t2g orbitals, whereas the dz2 and dx2-y2 orbitals are called the eg orbitals.

How will you distinguish between tetrahedral void and octahedral voids? ›

Tetrahedral void is a simple triangular void in a crystal and is surrounded by four spheres arranged tetrahedrally around it. On the other hand, an octahedral void is a double triangular void with one triangle vertex upwards and the other triangle vertex downwards and is surrounded by six spheres.

Why is octahedral called octahedral? ›

The octahedron has eight faces, hence the prefix octa. The octahedron is one of the Platonic solids, although octahedral molecules typically have an atom in their centre and no bonds between the ligand atoms.

What is a tetrahedral shape? ›

Tetrahedral is a molecular shape that occurs when there are four bonds and no lone pairs in the molecule's central atom. The atoms bonded to the central atom are located at the four corners of a tetrahedron, with 109.5° angles between them.

What shape is cucl42? ›

An isolated [CuCl4] 2− usually has a (meta)stable square planar or flattened tetrahedral structure. Careful studies [38, 39] show that the structure of [CuCl4] 2-exhibits a continuous distribution, with the most probable angle of about 136° between two Cu-Cl bonds.

Why is nicl4 tetrahedral? ›

In the given three complexes, each central metal atom is surrounded by four ligands. Thus, the four ligands occupy an additional one s- subshell and three p-subshells forming the hybridization \[s{p^3}\]. Thus, its geometry is tetrahedral.

What is complex ion? ›

A complex ion is an ion that contains one or more ligands that are attached to a central metal cation through a dative covalent bond. A ligand is a species that can form a dative covalent bond with a transition metal using its lone pair of electrons. H2O, NH3, Cl, OH, and CN are examples of ligands.

How do you name complex ions? ›

In naming the complex ion:
  1. Name the ligands first, in alphabetical order, then the metal atom or ion. ...
  2. The names of some common ligands are listed in Table 1. ...
  3. Greek prefixes are used to designate the number of each type of ligand in the complex ion, e.g. di-, tri- and tetra-.

Which of the following complex ion is tetrahedral? ›

The [CoCl4]2- complex ion is experimentally known to have a tetrahedral structure.

What is the shape of Cu NH3 4? ›

The shape of [Cu(NH3)4]^(2+) is square planar, Cu^(2+) in this complex is.

Why are complex ions Coloured? ›

As the oxidation state of the metal increases, so also does the amount of splitting of the d orbitals. Changes of oxidation state therefore change the colour of the light absorbed, and so the colour of the light you see.

Which complex ion is stable? ›

From ligand strength, we can see that CN− is strongest ligand among all so [Fe(CN)6]3− is most stable complex ion.

Which complex ion is positive? ›

A positively charged complex ion is called a cationic complex. A cation is a positively charged ion.

How do you write complex ion formulas? ›

Writing the (Line) Formula of a Complex:
  1. Identify the central metal ion.
  2. Identify the oxidation state on the central metal ion (shown in Roman numerals parantheses)
  3. Identify the ligands.
  4. Identify the number of ligands.
  5. Calculate the total charge on the ligands.
  6. Calculate the charge on the complex ion.

How do you know if a complex ion is a cation or anion? ›

Complex Ions, Ligands, & Coordination Compounds, Basic ...

How do you know the charge of a complex ion? ›

13.1 Deduce the charge and oxidation state of a central metal ion (HL)

Which complex ion does not have tetrahedral geometry? ›

Hence, the complex ion that does not possess a tetrahedral shape is (C) [Ni(CN)₄]²⁻. The correct option is (C) [Ni(CN)₄]²⁻.

What shape is cucl42? ›

An isolated [CuCl4] 2− usually has a (meta)stable square planar or flattened tetrahedral structure.

Which of the following complex has a shape different from others? ›

1 Answer. Explanation: [Zn(NH3)4]2+, Ni(CO)4 & [Cd(CN)4]2 all form tetrahedral structures where the central atom uses sp3 hybridisation.

What is the shape of CO NH3 6 3+ complex? ›

Hence, octahedral complex is formed.

What is the geometry of Cu NH3 4 2+? ›

Thus, [Cu(NH3)4]2+ has a square planar geometry.

Why is the complex Cu NH3 4 2+ square planar and not tetrahedral? ›

Solution. The oxidation state of Cu in [Cu(NH3)4]2+ is + 2. The electronic configuration of Cu2+ is 3d94s0. dsp2 hybridisation of one d, one s and two p orbitals result in square planar geometry.

Videos

1. Complex Ion Formation
(Professor Dave Explains)
2. The Shape of Complex Ions | A-level Chemistry | AQA, OCR, Edexcel
(SnapRevise)
3. Practising drawing complex ions from www.ChemistryTuition.Net
(ChemistryTuition)
4. Transition metal complex ions
(Allery Chemistry)
5. Shapes of transition metal complexes
(Dr de Bruin's Classroom)
6. GEOMETRY OF COMPLEXES/PGC
(PGC OFFICIAL EDUCATION)

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