Metal complexes with pyrazole-derived ligands Part I. Synthesis and crystal structures of 3-amino-4-acetyl-5-methylpyrazole (L) and of the tetrahedral complexes ZnL2(NO3)2 and ML2Cl2 (M=Cu(II), Hg(II))

A new pyrazole-derived ligand 3-amino-4-acetyl-5-methylpyrazole (L) has been synthesized and structurally characterized. In order to examine its coordination properties the metal complexes ZnL2(NO3)2, CuL2Cl2 and HgL2Cl2 have been prepared and their crystal and molecular structures determined by X-ray structure analysis. The crystals of the ligand are triclinic, space group P with unit cell dimensions a=14.433(4), b=7.406(1), c=6.794(4) A, α=99.81(4), β=92.10(9), γ=105.55(6)°, V= 686.8(5) A3; ZnL2(NO3)2 is orthorhombic, space group Pbca,a=18.420(2), b=14.892(2), c=14.114(2) A, V=3872(1) A3; CuL2Cl2 is monoclinic, space group I2/a,a=13.804(3), b=8.835(1), c=14.264(4) A, β=100.50(3)°, V=1710.5(7) A3; HgL2Cl2 is monoclinic, space group I2/a,a=14.075(2), b=9.002(2), c=14.303(3) A, β=97.39(2)°, V=1797.2(6) A3. The two latter complexes are isostructural. The ligand L acts as a monodentate ligand through the tertiary ring nitrogen atom. The complexes contain metal atoms in the distorted tetrahedral coordination realized by two nitrogen atoms from the two ligands L and two nitrate-oxygen atoms in the zinc complex and two chlorine atoms in the copper and mercury complexes. All four structures are built up from individual molecules linked together by hydrogen bonding interactions NH…O achieved between ‘pyrrole’ ring nitrogens of one molecule and the acetyl-oxygen atoms from the adjacent molecules. In the free ligand the additional hydrogen bondings NH…N occur also between amino and ‘pyridine’ nitrogen atoms of the neighboring molecules. The general physicochemical characteristics as well as the IR and 1H NMR spectra are in accordance with the observed molecular structures.