New Coordination Compounds of CuII with Schiff Base Ligands—Crystal Structure, Thermal, and Spectral Investigations

Abstract

The new mono-, di- and tetranuclear coordination compounds [Cu(HL1)]·H2O (1), [Cu2(L1)(OAc)(MeOH)]·2H2O·MeOH (2), [Cu4(L2)2(OAc)2]·4MeOH (3), and [Cu4(L2)2(OAc)2]·4H2O·4MeOH (4) were synthesized by the direct reaction of 2,2′-{(2-hydroxypropane-1,3-diyl)bis[nitrilomethylidene]}bis(4-bromo-6-methoxyphenol) (H3L1) or 2,2′-{(2-hydroxypropane-1,3-diyl)bis(nitriloeth-1-yl-1-ylidene)}diphenol (H3L2) and the Cu(II) salt. They were characterized by elemental analysis, X-ray fluorescence (XRF), Fourier transform infrared (FTIR) spectroscopy, simultaneous thermal analysis and differential scanning calorimetry (TG/DSC), and thermal analysis coupled with Fourier transform infrared spectroscopy (TG-FTIR) techniques and the single crystal X-ray diffraction study. In the dinuclear complex 2, the copper(II) ions are bridged by an alkoxo- and a carboxylato bridges. The tetranuclear complexes 3 and 4 are formed from dinuclear species linkage through the phenoxo oxygen atoms of the fully deprotonated H3L2. Compounds 1–4 are stable at room temperature. During heating in air, at first, the solvent molecules (water and/or methanol) are lost and after that, the organic part undergoes defragmentation and combustion. The final decomposition solid product is CuO. The main gaseous products resulting from the thermal degradation of 1–4 in a nitrogen atmosphere were: H2O, MeOH, CH3COOH, CH4, C6H5OH, CO2, CO, and NH3.

New Heterotrinuclear CuIILnIIICuII (Ln = Ho, Er) Compounds with the Schiff Base: Syntheses, Structural Characterization, Thermal and Magnetic Properties

“…The Cu(1) and Cu(2) centers have slightly distorted square pyramidal coordination geometries (Figures 5 and S3) in which the equatorial sites are occupied by two nitrogen and two oxygen atoms of Schiff base ligands. The Cu-O and Cu-N bonds are within normal values (C-O 1.913(4)-1.983(5) Å and C-N 1.960(5)-1.977(5) Å) and comparable to those observed in the related Cu II compounds [40,43,[46][47][48][49]. The apical positions are occupied by oxygen atoms from monodentate nitrate ions and the bond lengths are found to be significantly longer (distances in the range 2.410(6)-2.649(5) Å) than those of Cu-O in the basal plane.…”

“…The involvement of the phenolic oxygen atoms in the metal-ligand bonding is confirmed by the strong doublet bands observed at 1251 cm −1 , 1218 cm −1 1 and 1248 cm −1 , 1219 cm −1 2, respectively. The typical absorption band of the ν aryl -O vibration is identified in the free ligand spectrum at 1233 cm −1 [4,13,[38][39][40][41][42][43][44]. All these spectroscopic features are confirmed by the X-ray structures.…”

An Unprecedented Dodecanuclear Copper(II) Complex Derived from an Unsymmetrical Schiff‐Base Ligand

“…However, the coordination modes as well as hapticity of the ligands in this complex are different from each other. Here it should be noted that the possible coordination modes of symmetrical N 2 O 3 ligand derive from condensation of 1,3‐diamino‐2‐propanol with o ‐hydroxyacetophenone or its derivatives are reported by Bartyzel et al [5j] . Coordination features of the ligands in this complex are depicted in Scheme 2.…”

Covalence and π-electron delocalization influence on hydrogen bonds in proton transfer process of o-hydroxy aryl Schiff bases: A combined NMR and QTAIM analysis

“…These compounds have been extensively investigated due to their physical-chemical properties, such as thermochromism and photochromism, role played in catalytic biochemical processes, coordination chemistry, organic synthesis, technological applications, and design of anticancer drugs. [50][51][52][53][54][55][56][57][58][59][60][61][62][63][64] Some o-Hydroxy aryl schiff bases present a keto-enol tautomeric equilibrium [see Figure 1] which is a consequence of a proton transfer process in the intramolecular HB that gives rise to two tautomeric forms, enol-imine (or OH-) and ketoamine (or NH-). [65][66][67][68] Spectroscopic data obtained by applying different techniques such as heteronuclear NMR in both phases, FT-IR spectroscopy, X-ray and neutron diffraction, have shown that OH form predominates in solution, with a few exceptions, while in the solid state the tautomeric equilibrium is strongly shifted towards to the NH form.…”