Columnar Stacks Versus Metal-Involved Dimers: Supramolecular Behavior of Square-Planar Cu(II) Complexes with Deprotonated N-(Pyridin-2-yl)ureas

A series of new square–planar Cu(II) complexes with deprotonated N-(pyridin-2-yl)ureas (Cu(L)2, where LH = 1,1-dialkyl-3-(4-R-pyridin-2-yl)urea) was synthesized and characterized by elemental analysis, HRMS, and IR spectroscopy. The structure of all synthesized compounds was determined by the single crystal X-ray diffraction (XRD). The supramolecular architecture is governed by the number of methyl substituents in the pyridine ring. Monosubstituted derivatives form infinite columnar stacks due to π···π stacking, whereas dimethylpyridine analogues form discrete dimers due to direct intermolecular Cu···O or Cu···C contacts. DFT calculations (QTAIM, NCI, IRI) confirmed the nature of these noncovalent interactions. The possibility of Cu/Pd isostructural substitution in such complexes is shown, which opens up additional prospects for the crystal chemical design of materials based on these ligands.