Google is just one of the tenants along with Food Network and Major League Baseball. They also own the building across the street, 111 Eighth Ave. Some other companies rent space in there too. Google has the cash, doesn't want to pay rent, and knows they are going to be there for a long time. Might as well buy the place. Not really a tax avoidance, although it certainly could be, but it's more like a cost avoidance. Estimated rent for 1.2m sqf is $6.1m/month for your typical office space in Chelsea. For a price of $2b, Google would get their money back in 30 years from collecting rent, assuming it never changes. I'm sure they are looking at closer to 15 years.