City Owned Properties in Queens & Brooklyn

Good afternoon, I have noticed there are a LOT of vacant homes in Queens (New York City), which have been vacant for at least 7 or 8 years. After doing a little research I have found that a majority of them are city owned. Some of them were put up for auction but received no bids.

I would like to purchase a few of these properties. I have contacted the city (in different ways), but have yet to receive a response.  Does anyone have any knowledge or experience with purchasing properties from the city?

Thanks in advance!