Dicatenar pyridylpyrazoles: An opportunity to induce mesomorphism. Synthesis, X-ray characterisation and DFT calculations

Abstract

The molecular structure of the N,N’-donor dicatenar pyrazole derivative 3-(3,5-bis(decyloxy)phenyl)-(5-pyridin-2-yl)pyrazole [HpzR(10,10)py] (R=C6H3(OC10H21)2) has been studied by single crystal X-ray diffraction and analysed using Hartree–Fock (HF) and density functional theory (DFT) computations. The molecular electrostatic potential (MEP) and the natural bond orbital (NBO) analysis show the ability of these pyrazoles to establish coordinative bonds and intermolecular interactions in the crystal state. In fact, the [HpzR(10,10)py] molecules form dimers through N–H⋯N hydrogen bonds, generating a four-chained decorated disc-like core. The HOMO and LUMO electronic properties and energies were also measured. On the other hand, the coordination of this promesogenic ligand to Pt(II) was strategically used to achieve a metallomesogenic material with improved luminescence properties. Thus, the compound [Pt(pzR(10,10)py)2], in which the pyridylpyrazole is coordinated in its deprotonated form as a pyrazolate ligand, was proved to be a bifunctional luminescent liquid crystal material. The π–π stacking of its disc-shaped molecules found in the crystalline solid is related to that of hexagonal columnar mesophase exhibited at 83°C.