Tax benefits from the purchase I think. They were saving something like $700m a year in taxes for a bunch of years following the purchase. I forget the details.

Motorola was bleeding money when Google purchased them. Google can deduct the operating losses from their profits to reduce their tax burden.

In addition, Motorola likely has many depreciating capital assets, and when the loss was booked by the sale, they can also write those off from their profits. A deal like this will have tons of tax lawyers going through them to maximize their benefits.