## 2012 Quiz 3 Number 4

LRoudebush 1A
Posts: 5
Joined: Fri Sep 26, 2014 2:02 pm

### 2012 Quiz 3 Number 4

The question asks how many NH2CH2CH2NH2 ligands would be formed in a square planar complex with Pt2+ as the central metal ion. I understand that the two nitrogen donors connect to the central metal atom. But how would you use the information that this complex is square planar to help solve this problem?

Posts: 15
Joined: Fri Sep 26, 2014 2:02 pm

### Re: 2012 Quiz 3 Number 4

Think back to geometries in Chapter three. Knowing that the shape is square planar tells us that there are 6 available binding sites for the central atom, but only 4 are being occupied by bonds (there are lone pairs present in the other two spots). So, 2 NH2CH2CH2NH2 bond with the atom to give that shape. Attached is a picture explaining what a square planar geometry is to make understanding this problem easier.
Attachments square_planar_molecular_geometry.jpg (11.81 KiB) Viewed 596 times

GinaYoung1L
Posts: 16
Joined: Fri Sep 26, 2014 2:02 pm

### Re: 2012 Quiz 3 Number 4

Information about the geometry of the complex allows us to determine the number of bonds that the central metal will form. In this case, platinum ion is the center of a square planar complex. A square planar complex has four corners and therefore four bonds to the ligand(s). This particular ligand is bidentate, so it can form two bonds with the central metal. Hence, we need two of these bidentate ligands to form a total of four bonds which will fulfill the square planar shape.

Remember: in the octahedral complex, the tetrahedral complex, and the square-planar complex, the ligand(s) bonds with the central metal at the corners of the particular geometry. Look back at page 99 of the course reader.

RaquelAvalos1K
Posts: 35
Joined: Fri Sep 26, 2014 2:02 pm

### Re: 2012 Quiz 3 Number 4

I'm pretty confused about drawing ligands.

How do we know that N attaches, and not C?

Does the Pt2+ have any real significance then? In figuring this out, would we be drawing how it looks?

Also, we assume that the other 4 bonds are being occupied by another compound, so the NH2CH2CH2NH2 would have to occupy the available spots?

GinaYoung1L
Posts: 16
Joined: Fri Sep 26, 2014 2:02 pm

### Re: 2012 Quiz 3 Number 4

You can expect N to bond to the metal center because of its lone pair. An important characteristic of C is that it forms four bonds. On rare occasions would it deviate from that general pattern.

In this problem, you do not need to know that Pt has a +2 charge in order to figure out how many (en) ligands exist in this structure.

Personally, I don't need to draw it out in order to figure out the answer to this problem because 1) we are given the square-planar geometry of the complex and 2) we can figure out that (en) is a bidentate ligand due to its two N atoms. Therefore, we need two of these ligands to make a total of four links with the metal center.

No, there are no other compounds occupying the available bonds of the Pt2+. In the square-planar geometry of this complex, each (en) ligand occupies two vertices of the geometry. Therefore we need two ligands to occupy a total of four vertices.