Synthesis, Structure And Properties Of Pyrazole Ligands And Their Complexes

Pyrazole ligands and their complexes have broad application prospects in many respects, such as gained great attention in the field of coordination chemistry, biological simulation, fluorescence and magnetism as well because of their novel structures and great binding complexing ability, and many researchers have focused on this area nowdays. In this paper dissertation, three kinds of singulary 1-substituted monopyrazole Ligands, Pyrazolylalkanol, Pyrazolylpropanamide and Pyrazolylacetamide Ligands were synthesized and characterized, and also their new metal complexes were investigated. The single crystal structures of pyrazole ligands and their complexes were examined, and the properties of the complexes were also tested. This investigation may provide a good foundation for the study of pyrazole ligands and their complexes in novel structures.Three intermediates of the monopyrazole compounds 3,5-dimethylpyrazole, 3-(2-pyridyl)pyrazole and 5-methyl-3-phenylpyrazole, were prepared by 1,3-dione compounds and hydrazine hydrate. These intermediates were treated with acrylamide and 2-chloroacetamide by the Michael addition to afford six new monopyrazolylamides ligands as follows: 3-(3,5-dimethyl-1H-pyrazol-1-yl)-propanamide (L²), 3-[3-(2-pyridyl)-1H-pyrazol-1-yl]propanamide (L³), 3-(5-methyl-3-phenyl-1H-pyrazol-1-yl)propanamide (L⁴), 2-(3,5-dimethyl-1H-pyrazol-1-yl)acetamide (L⁵), 2-[3-(2-pyridyl)-1H-pyrazol-1-yl]acetamide (L⁶) and 2-(5-methyl-3-phenyl-1H-pyrazol-1-yl)acetamide (L⁷). The characterization of these six ligands was performed by elementary analysis, MS, IR and NMR spectrum. In addition, the crystal structures of L⁴ and L⁷ ligands were obtained using the solution method and determined by X-ray diffraction analysis, which proved that the L⁴ ligand containing one molecule of water is orthorhombic with space group P2₁2₁2₁ and the L⁷ ligand is triclinic with space group P–1.Five new complexes were synthesized by 1,3-bis(3,5-dimethylpyrazol-1-yl)- propan-2-ol (L¹) and above six ligands coordinating with Cu(â…¡), Zn(â…¡), Ni(â…¡) and Co(â…¡) ions, and their structures were charactered by IR spectrum and four among them with single crystal structures were characterized by X-ray diffraction as follows: [Zn₂(C₂H₅OH)₂(C₁₃H₂₀N₄O)₂](ClO₄)₂ (1), Zn(C₁₁H₁₂N₄O)Cl₂ (2), [Cu(C₁₁H₁₂N₄O)Br₂](CH₃OH) (3), Cu₂(C₈H₆N₃)₂Cl₂ (5). The complex (1) is triclinic with space group P–1, and the organic ligand is coordinated with Zn²⁺ ion to produce a five-coordinate dinuclear complex which has two square pyramidals. The complex (2) is four- coordinate mononuclear forming a tetrahedral geometry and is triclinic with space group P–1. In this crystal structure, there are two intermolecular interactions: hydrogen bonds andÏ€-Ï€stacking. The complex (3) is the same as (2) expect that (3) is five-coordinate and has a square pyramidal geometry. The four-coordinate dinuclear complex (5) is centrosymmetric and monoclinic with space group P2₁/c. There is no hydrogen bond in its crystal structure in complex (5). Thermal decomposition mechanism of the obtained complexes was examined.Thermogravimetric analysis indicated that the outer small molecules were firstly broken down and the inner organic parts were dissociated. Additionally, the fluorescence spectrum of some complexes was tested and the results indicate that pyrazolylamide zinc complexes have promising fluorescence performances.