Pyrazolylpyrimidines are of interest from various viewpoints. They demonstrate biological activities as cytoprotectors [1] and cardiotonic agents [2]. These compounds can act as ligands for the, synthesis of coordination compounds because of the presence of donor atoms. By varying the number and the position of the substituents in the pyrazolylpyrimidines, coordination compounds with catalytic or interesting magnetic properties can be obtained [3]. Pyrazolylpyrimidines are also very appealing ligands in the design of spin-crossover systems similar to those obtained earlier with the related azine systems pyrazolylpyrazines and pyrazolylpyridines. As part of a continuing search for study on applications of Hirshfeld surface (de & dnorm surface) and 2D fingerprint plots [4] in visualizing and analyzing intermolecular interactions and relationship between intermolecular contacts and molecular geometry of polymorphic structures, we have now report the Hirshfeld surface and packing analysis of Three differently coloured (green (G), emerald green (EG) and orange (O)) (4-(3´,5´-dimethyl-1H-pyrazol-1´-yl)-6-methyl-2-phenylpyrimidine)dichlorocopper(II) polymorphic structures. In this study de and dnorm surfaces for each polymorphic structures calculated and constructed (Fig. 1) and break down of fingerprint plots used for decoding of intermolecular contacts. In conclusion we can suppose that the possible reason for the difference in colour between the three polymorphs is the presence or absence of π–π stacking. It is interesting that when π–π interactions result in infinite stacks (2O), the density, packing coefficient and uniformity of the crystal packing notably decreases. It seems as though in this case the loss in energy of the non-directed van der Walls intermolecular interactions is compensated for by the energy of π–π stacking.

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