Pamoic acid-phenanthroline co-crystal and its Cu(II) complex: X-ray structures and luminescence properties

Abstract

In this study, pamoic acid-phenanthroline proton transfer complex [(HPhen)(HPam)] and its Cu(II) complex {[Cu(Phen)2(H2O)2]Pam·2.5H2O were prepared and characterized by spectroscopic and analytical methods. The structures of the compounds were determined by single crystal X-ray diffraction studies. In the structure of the proton transfer complex [(HPhen)(HPam)], one of the carboxyl group proton of a pamoic acid molecule transferred to the one of phenanthroline nitrogen atom. In the structure, no hydrogen bond contacts were observed between the protonated phenanthroline (HPhen)+ and mono-deprotonated pamoic acid (HPam)- and phenanthroline (HPhen)+ cations involve in a hydrogen bond (N1-H····O7) with a DMF solvate. Hydrogen bonds between mono-deprotonated pamoic acid [HPam]- anions and π-π stacking interactions play a crucial role in the packing of the structure. X-ray crystallographic data showed that the Cu(II) complex consists of [Cu(Phen)2(H2O)2]2+ cationic unit, a pamoate counter anion and lattice water molecules (2.5H2O per complex cation). In the structure, each Cu(II) ion are six-coordinated and bound to four nitrogen atoms of two phenanthroline ligands and two water ligands with a distorted octahedral geometry. The pamoate anion does not involve in coordination with Cu(II) ion. The cationic units are linked by intermolecular hydrogen bonds forming a 2D hydrogen bond network. 2D hydrogen bond network further extended to 3D network by π-π stacking interactions. Absorption and emission spectral features of the compounds were investigated both in the solid state and solution.