Synthesis, Characterization, Crystal Structure and Antimicrobial Activity of Copper(II) Complexes with the Schiff Base Derived from 2-Hydroxy-4-Methoxybenzaldehyde

Pahon?u, Elena; Ilie?, Diana-Carolina; Shova, Sergiu; Paraschivescu, Codru?a; Badea, Mihaela; Gulea, Aurelian; Ro?u, Tudor

The ligand HL structure is shown in Figure 3 . The planar configuration of HL molecule is stabilized by an intra-molecular O-H⋅⋅⋅N hydrogen bond which is observed in the majority of Schiff base ligands obtained from 2-hydroxybenzaldehyde [28] . The crystal packing of HL is stabilized by π-π staking and C-H···O cooperative interactions. Cg1 (the centroid of the C-C9 ring) exhibits a stacking interaction with Cg2 (the centroid of the C11-C16 ring) of the adjacent molecule, related by two-fold axis, with a centroid-to-centroid distance of 3.851(4) Å. The formed dimeric units ( Figure 4 ) are further associated due to the presence of weak C-H···O intermolecular interactions resulting into the formation of two-dimensional supramolecular ribbons, as the main crystal structure packing motif, depicted in Figure 5 . Tables 1 and 2 . Complex 6 has a crystal structure formed from the complex binuclear cations [Cu2(L2S)2(ClO4)(H2O)] + , ClO4 − anions and H2O as solvate molecules 1:1:1 molar ratio. The structure of the complex cation is presented in Figure 6 . In the complex cation two Cu 2+ ions, separated by 3.029(1) Å, are coordinated by two mono-deprotonated HL − ligands, so that the charge balance is in agreement with the formation of species [Cu2(L2S)2ClO4H2O] + . The separate structure of the coordinated ligands along with the atomic labeling scheme is presented in Figure 7a ,b. Both the ligands are identical from the chemical point of view and exhibit very close geometric parameters ( Table 2 ). The localization of the hydrogen atoms using the difference density Fourier map has clearly shown that the non-coordinated azomethine atoms N1 and N4 are the sites of protonation associated with the hydrogen bonding towards phenolic oxygen atoms as acceptor (Figures 6 and 7) . The copper atoms adopt a slightly distorted octahedral [O4NS] coordination completed by ClO4 − anion and H2O molecule as monodentate ligands for Cu1 and Cu2, respectively ( Figure 8 ). The crystal structure of complex 6 is characterized by the parallel packing of two dimensional supramolecular layers consolidated due to the numerous O-H···O and C-H···O hydrogen bonding, as shown in Figure 9 .