Firstly, your Nikon D300s is more than adequate for the job, but a fast-wide lens (zoom or prime) will definitely help in producing a more desired look. (more about this is a little later)

Secondly, for the Events Manager to approach you, suggests that he is not completely satisfied with his current image types.

So, the question is, what are the Events Managers pain points and what can you as a photographer do to satisfy his requirements?

Perhaps this is a question you need to ask before endeavouring on purchasing any new equipment.

With this out of the way, having worked on and off as a freelance events/wedding photographer for many years, this is my take on it.

1. The current images do not show off the venue.
2. These images can be from anywhere where people are gathered and having fun.
3. There are no distinguishing features in any of the images that show off the club.
4. The club does not look attractive or appealing.
5. The flash has ensured that the light fall of is too quick and therefore leaving the background dark and unappealing
6. If these images are shared on social media, it can be difficult to determine which club they belong to.

However, saying that, this maybe just what the manager wants; for his clientele to visit a gallery of themselves. Perhaps with a view to selling merchandise such as insta-prints, key-rings and other products.

However, this is not always the case and what the managers generally want, is to show people having fun inside a recognisable and attractive venue that potential clubbers will be attracted to.

In my experience, I found Managers always wanted to sell the venue and not just the clubbers when these images are shared on social media so that they generate popularity and more customers.

A fast-wide angle lens such as the Tokina AT-X Pro 11-16mm f/2.8 DX Nikon Lens for about $500 amongst many others, will ensure that you are able to capture the ambient beauty, the clubs appeal and the attractiveness of the venue whilst capturing clubbers and images of big crowds.

It provides sufficient focal range for both extreme wide angles for groups at close range and a 24mm full frame equivalent at the 16mm end for even closer shots with minimal lens distortion, all whilst maintaining a constant f/2.8.

If you are not keen on the ultra-wide look, then you have options for 17-50mm f/2.8 from Tamron at under $400 but you will lose quite a significant amount of FOV. Means you will need to be creative.

And then, by adding a cheap $50 flash to complement the ambient light you will provide an overall pop to the image and also not have to worry too much about camera shake.