  We present results from the XMM-Newton observation of the binary cluster
A1750 at z = 0.086. We have performed a detailed study of the surface
brightness, temperature and entropy distribution and confirm that the two main
clusters of the system (A1750 N and A1750 C) have just started to interact.
  From the temperature distribution, we calculate that they are likely to merge
sometime in the next 1 Gyr. The more massive cluster, A1750 C, displays a more
complicated temperature structure than expected. We detect a hot region
associated with a density jump ~450 kpc east of the cluster centre, which
appears to be a shock wave. This shock is not connected with the binary merger,
but it is intrinsic to A1750 C itself. From simple physical arguments and
comparison with numerical simulations, we argue that this shock is related to a
merging event that A1750 C has suffered in the past 1-2 Gyr. The larger scale
structure around A1750 suggests that the system belongs to a rich supercluster,
which would presumably increase the likelihood of merger events. These new
XMM-Newton data thus show that A1750 is a complex system, where two clusters
are starting to interact before having re-established equilibrium after a
previous merger. This merger within a merger indicates that the present day
morphology of clusters may depend not only on on-going interactions or the last
major merging event, but also on the more ancient merger history, especially in
dense environments.
