In this manuscript we report the synthesis and X-ray characterization of several complexes of Cu(II) with a 2-(1H-pyrazol-1-yl)-pyrimidine (L) ligand. Complexes CuLCl2 (1), [CuL2(H2O)2](NO3)2 (2) and [CuL2H2O](NO3)2 (3) are mononuclear systems and [CuL(NO3)2]n (4) is polymeric. In the solid state, complexes 2 and 3 are characterized by the presence of anion–π interactions that are relevant for the final 3D architecture and packing. In complexes 1 and 4, where the counterion is directly bonded to the metal, anion–π interactions are not observed. High level ab initio calculations (RI-MP2/def2-TZVP) have been used to evaluate the noncovalent interactions observed in the solid state and the interplay between them. We also demonstrate that the presence of anions above the aromatic ligand is not due only to strong electrostatic interactions between the counterparts.
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