It is probably the summer heat. Does not look like clematis wilt. Remove all the grass within a foot of the crown, apply some cow manure/alfalfa pellets. Cover the area with mulch. Keep it watered well and everything should be fine. You should start working on a better trellis for the plant to climb on. Depending on type and sun/shade requirements, flowering should happen next spring. Once you see the flowers and determine what type the plant is, there is a likely hood that the plant will have to be moved to a better location. But that can wait. Good news is that even if the plant seems dead, it will come back to life next spring. New shoots will start coming up from the crown. Hope you planted it so that the crown is under six inches of soil. This encourages new shoots to come up.

Thank you, I'll definitely do as you suggest.