Two Cu^II complexes of 3,4,5-tri-methyl-1H-pyrazole

The crystal structure of complexes of 3,4,5-tri-methyl-1H-pyrazole with CuCl₂·2H₂O and Cu(NO₃)₂·2.5H₂O are presented, namely di-μ-chlorido-bis[chloridobis(3,4,5-trimethyl-1H-pyrazole-κN²)copper(II)], [Cu₂Cl₄(C₆H₁₀N₂)₄] (1) and aquatetrakis(3,4,5-trimethyl-1H-pyrazole-κN²)copper(II) dinitrate, [Cu(C₆H₁₀N₂)₄(H₂O)](NO₃)₂ (2), and compared to the previously determined structures for 3-methyl-1H-pyrazole and 3,5-di-methyl-1H-pyrazole. CuCl₂ forms a 2:1 ligand-to-metal chloride-bridged complex with 3,4,5-tri-methyl-1H-pyrazole, with a square-pyramidal coordination geometry about each copper(II) center. Similarly to the previously obtained 3,5-di-methyl-1H-pyrazole complex with CuCl₂, the pyrazole ligands are cis to each other, with two chloride ions bridging the two copper(II) centers, and a terminal chloride ion occupying the axial position. Cu(NO₃)₂ forms a 4:1 ligand-to-metal complex with 3,4,5-tri-methyl-1H-pyrazole that is also arranged in a square-pyramidal geometry about Cu^II. The newly obtained copper(II) complex has the same coordination geometry as the 3,5-di-methyl-1H-pyrazole complex, including an axial water mol-ecule, two nitrate ions hydrogen-bonded to the water mol-ecule, and four pyrazole ligands in the equatorial plane, suggesting that similar steric forces are at play in the formation of these complexes.