Question 3 on the Homework for Week 9

[Sydney Rohan 3G]

I am confused about question 3 on the homework. The question state:

Which geometry or geometries are common for complexes with a coordination number of 4?
a) tetrahedral
b) seesaw
c) square planar
d) trigonal bipyramidal

I figured out that tetrahedral would be one of the answers, but I can not figure out which other answer is correct. Can someone please help?

[305597516]

In the lecture, the professor said that 4 ligands could mean either tetrahedral or square planar, but you are not expected to know which is which (when seeing just a formula I think). So I think the other answer would be square planar. I think seesaw is a possible structure, but is just not common like we see with square planar and tetrahedral, so we would not consider it in this answer.

[Nithya Madhu 2L]

Hey,
Basically for coordination number we are only looking the number of bonds to the central atom, not the lone pairs.
Since tetrahedral and square planar have 4 bonds to the central atom, they have a coordination number or 4.
And even though square planar has 2 lone pairs, this does not matter for the coordination number since we are only looking at the bonded atoms/molecules to the central atom.
Hope that helps!