If the concrete is level both sides of the crack, I would look at the shuttlers ditra product. Not sure of spelling. It is an orange mat. I think home depot sells it. I am planning on using it over a expansion joint where the old garage floor met the house floor. I am going to tile over the area where there was a 2x4 for expansion joint. I have not done it yet, but I think this is a good product.

Fill the crack first. If there is no lippage on either side, you should be ok. If there is lippage, you have a sub slab issue and I would not tile in this area. Perhaps a floating floor would serve you better and not need to tight against a moving floor. If the crack continues, you might be looking at the tiles popping off sooner than later....

schluter, not shuttlers ;-) altho i wouldn't use anything but a sealant on david's expansion joint but it is his home,,, 1st determine IF the crk is static OR dynamic in its reaction to temperature,,, if static, do whatever you want BUT 1st, as amazing notes, make sure 1 side of the crk isn't appreciable higher than the other,,, IF you find the crk is dynamic, rethink your flooring choices