The goal for these negotiations is to reach a mutually-agreed long-term comprehensive solution that would ensure Iranˈs nuclear program will be exclusively peaceful.
while we have a noun phrase "the goal" connected to another noun phrase "these negotiations", why isn't of used instead of for?
The use of "for" vs "of" in that example is hard to explain, and I think it's more of a question of style than correctness. It doesn't feel right say that any one thing is the goal, or even a goal "for" a person. That somehow says that the person is less important than the goal, whatever that goal may be. However, in your example you quote the goal "for" an activity. That works; the goal is the entire purpose of the activity. "Of" would work there too.
I'd like to point out something else about the phrase. To refer something as the goal of something or someone, that goal needs to be the primary purpose.
For instance, it is the goal of a teacher for the students to learn the material. However, it is a goal of Mrs. Brown (the teacher) for her students to learn. In other words, Mrs. Brown has other priorities too, she's not just a teacher. Perhaps she's a wife, mother and Scrabble player too. So the big difference here isn't the use of "for" vs "of", the important distinction is between "a" or "the".
IMHO, goal for suggests a third party stating (or predicting?) the goal. If goal of is used instead, it might would have suggest the authentic/declared goal.
For examples -
The goal for you is to pass with high grades in this examination - Maybe, the parents have predicted (or set) goal for their kid. On the other hand...
The goal of him is to pass with high grades in this examination - It's pretty confirmed from a pupil's side!
