It's a bit more complicated than that.
All male tions and ligers so far observed have been infertile. This is not the case for the females.
Consequently you can have Li-tions and Ti-ligers etc.
http://www.lairweb.org.nz/tiger/tigons.html
The definition of a species is not as solid as saying they must be able to produce fertile young.
Firstly that doesn't help you with asexual reproduction species secondly it's a bit difficult to test. Per haps a black widow spider could have fertile off spring with a funnelweb - Good luck in convincing them to try!
Thirdly as already pointed out e - hybrids between dogs and Wolves spring to mind but here's a specific example
http://news.bbc.co.uk/1/hi/sci/tech/5080298.st m