In general, if the atoms that make up the ring contain heteroatoms, such rings become heterocycles, and organic compounds containing heterocycles are called heterocyclic compounds. An article called Why are the {Cu4N4} rings in copper(I) phosphinimide clusters [Cu{μ-N:PR3}]4 (R = NMe3 or Ph) planar?, published in 2015, which mentions a compound: 75732-01-3, Name is Mesitylcopper(I), Molecular C9H11Cu, HPLC of Formula: 75732-01-3.
The Cu phosphinimide complexes [Cu{μ-N:PR3}]4 (1, R = NMe2 and 2, R = Ph) were obtained in good yields from the reactions of Cu[Mes] (Mes = mesityl, C6H2Me3-2,4,6) with the corresponding iminophosphoranes, HNPR3. The mol. structures of 1 and 2 reveal planar eight-membered {Cu4N4} rings which contrasts with the saddle-shaped {M4N4} rings found in related metal phosphinimide complexes. According to computations, there is negligible aromaticity in the planar {Cu4N4} rings in 1 and 2 and the saddle shape observed in related {M4N4} rings is due to steric factors.
In addition to the literature in the link below, there is a lot of literature about this compound(Mesitylcopper(I))HPLC of Formula: 75732-01-3, illustrating the importance and wide applicability of this compound(75732-01-3).
Reference:
Iodide – Wikipedia,
Iodide – an overview | ScienceDirect Topics – ScienceDirect.com