SYNTHESIS, X-RAY CRYSTAL STRUCTURE, SPECTROSCOPIC CHARACTERIZATION AND MALDI MASS SPECTRA, HIRSHFELD SURFACE ANALYSIS OF OCTANUCLEAR AZAMETALLACROWN COPPER(II) COMPLEX WITH 3,5-DIMETHYL-1H-PYRAZOLE, OBTAINED BY OXIDATIVE DISSOLUTION METHOD

A novel copper(II) polynuclear complex with deprotonated 3,5-dimethyl-1H-pyrazole of composition Cu8(µ3-O)2(DMPZ-Н)8(NCO)2(OAc)2·2CH3OH has been synthesized and isolated in the crystalline state. A variety of techniques were employed to identify and characterize the structure of the complex, including IR spectroscopy, microanalysis, MALDI analysis, and single-crystal X-ray diffraction. It was observed that Cu8(µ3-O)2(DMPZ-Н)8(NCO)2(OAc)2·2CH3OH had been formed as a result of a multistage process of oxidative dissolution of metallic copper with the participation of air oxygen and ammonium ions. This process results in the accumulation of a sufficient concentration of Cu²⁺ ions in the solution, which contributes to both the formation of the final product and the dissolution of metallic copper through the intermediate generation of Cu⁺ species. These intermediates are subsequently oxidized by atmospheric oxygen to yield divalent copper compounds. The resulting octanuclear complex Cu8(µ3-O)2(DMPZ-Н)8(NCO)2(OAc)2·2CH3OH is a new inverted 24-azametallocrown-8, due to the implementation of the cyclic interaction (-Cu-N-N-)8 formed by eight copper ions and eight μ2-bridge coordinated 3,5-dimethyl-1H-pyrazole anions. A crystallographic 2-fold axis bisects the obtained octanuclear complex on the same two trinuclear fragments Cu2-Cu3-Cu4i and Cu2i-Cu3i-Cu4, which are sequentially linked by deprotonated bidentate-bridging coordinated molecules of 3,5-dimethyl-1H-pyrazoles and bridging μ3-O2-, which are the centers of coordination for three copper cations. Tetradentate-bridged cyanate groups additionally assemble the thrinuclear fragments into an octanuclear complex. Hirshfeld surface analysis, complemented by two-dimensional fingerprint plots, was carried out to investigate the intermolecular interactions in the crystal structure. The results revealed dominant H···H contacts (71.7 %) along with notable contributions from H···C/C···H, H···O/O···H and H···N/N···H interactions, confirming that hydrogen bonding plays a significant role in stabilizing the crystal packing.