The Ayatollah has told hardliners in Iran to give the newly-elected, relatively moderate president, Hassan Rouhani, a chance to make diplomacy work. The motivation is the same force that put Rouhani into power - the public outcry in Iran for relief from the crippling economic sanctions.

But speaking via Skype from the Center for Security Studies in Zurich, senior researcher Roland Popp said the motivation goes only so far.

“I think they’re willing to compromise, but they’re not willing to capitulate. On the one side, there is great support for the nuclear program. It’s kind of a matter of national pride," said Popp. "On the other side, people look very much into their economic surroundings and people expect the politicians to negotiate those sanctions away.”

Experts say that means finding a formula to limit Iran’s nuclear program that assures the international community it is not trying to build a bomb - without requiring an end to the program, as some in the international community would like. Also, there will have to be enough sanctions relief to satisfy Iran in the short term, without removing its motivation for further concessions in a long-term deal.

“The big sanctions, which are in fact the oil and financial sanctions, are not going to be waived or undone at this point,” said Rifkind.

But that is what Iran wants at the end of this process, perhaps in six months. So as difficult as these negotiations have been, if they succeed, even harder work, and more painful compromises on both sides, lie ahead.