There are certain friendships and convergences in international politics which are either out of necessity or due to convenience or both. And when one thinks of such alliances of convenience, the Turkey and Iran friendship is the most proper and obvious option. There are many reasons why this unholy alliance finds it is so convenient for them to join forces. The basic fact is the presence of Saudi Arabia and its allies as the pre-eminent power in the Middle East and the aim of both Turkey and Iran to take its place.
For Turkey and Iran to take place of Saudi Arabia, Riyadh needs to be removed from its place, and the unholy alliance of these two countries can last for that long only. The two countries have been desperately looking for finding a way to increase their influence in the region to a level that they can challenge the Arabian countries. However, the convergences are less than the number of divergences and differences.
First, let us talk about the convergences. Both Iran and Turkey are supporting the Hamas and Muslim Brotherhood, for their own different reasons, however, Iran is also supporting the Haqqani network too. These organisations are working in their own ways to either in the name of supporting the Palestinian cause attacking Israel or creating disruption in the Arabian Peninsula to make it difficult for Riyadh.
Turkey has been disrupting the whole region, with the basic understanding that, if it is not able to gain prominence at a time of status-quo, then, it will be better to stir things up and manoeuvre in the new equilibrium. Turkey is using terrorists as militia on rent as its forces to destabilise Syria, Libya, and Nagorno-Karabakh and now as per reports even in India. Similarly, Iran also wants these regions to be disrupted, the reason being that, as per its dominance designs, and it wants to support its Shia proxies in all of the Middle East and gain control of other regions on the expense of Saudi Arabia.
Iran and Turkey both are looking to find ways to gain nuclear capabilities and in this stride too, both find convergence. Recently, the trade between Iran and Turkey, too, has substantially increased, notwithstanding the US sanctions on Tehran. Iran and Turkey are also working together to decrease the influence of OPEC as well as the OIC (Organisation of Islamic Countries) and create a parallel organisation too.
However, these convergences seem minuscule in front of the large differences between the two countries. First comes the elephant in the room, that is, one is a Shia theocracy the other is fast turning into a Sunni theocracy. In this scenario, both will find it difficult and awkward to stick together and soon will diverge towards becoming enemies. Iran has real interests in maintaining its relations with Armenia; however, Turkey finds itself on the other side by backing Azerbaijan.
The Israel factor is strong on the Iranian side, while Turkey has long been an ally of Israel and is acting as a distant relative just to further its political ambitions in the region. On the other hand, Pakistan too is an important ally of Turkey, but a nuisance state for Iran. Given all these features of Iran Turkey bilateral relations, the unholy alliance will not last long and will evaporate with the passage of time.