Isostructural coordination polymers of the tethering naphthalene anchored bis(2-methylpyridinecarboxamide) ligand: single crystal, XPS, EDS and theoretical studies

Abstract

This research work reports the synthesis of three novel coordination compounds with the formula {[M(L1)(C₃H₇NO)₄].(ClO₄)₂}_n (M = Cu(II) 1, Co(II) 2, and Zn(II) 3), using M(ClO₄)₂·6H₂O metal salt with L1 (where L1 = (N²,N⁶-bis(pyridin-4-ylmethyl)naphthalene-2,6-dicarboxamide). Diffraction study shows that these compounds are isostructural 1D coordination polymers which is also confirmed using XPac 2.0 software. In addition, information on the chemical state of metal ions, and chemical environments around different elements viz. C, N, O and Cl was obtained by the XPS analysis of these compounds. EDS analysis was done on these compounds, which further supports the findings of XPS and single crystal diffraction studies by showing the presence of respective elements of the ligand, perchlorate ion, and metal ions in the bulk samples. DFT studies on L1 and compounds 1–3 were performed considering the effect of solvent molecules on the HOMO–LUMO energy gap, which shows the order of 4.609 eV (2) < 4.737 eV (3) < 4.742 eV (1) < 4.752 eV (L1). Furthermore, the total energy (E_Total) of the metal ligand coordination bond in the compounds 1–3 is calculated, which is further decomposed into various contributing energies. A more negative value of E_Total in 1 reflects the effect of Jahn–Teller distortions and is in good agreement with the crystallographic metal ligand bond distance. Besides, various analytical techniques viz. NMR, IR, etc. were used to characterize the ligand and compounds as well. The phase purity of these compounds was determined using PXRD.