Copper(II) complexes with semicarbazones: synthesis, characterization and noncovalent interactions in their crystal stru
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Copper(II) complexes with semicarbazones: synthesis, characterization and noncovalent interactions in their crystal structures CLAUDIA C GATTO*
, FRANCIELLE C LIMA and PATRI´CIA M MIGUEL
Laboratory of Inorganic Synthesis and Crystallography, University of Brasilia (IQ-UnB), Campus Universita´rio Darcy Ribeiro, CEP 70904970 Brası´lia, DF, Brazil E-mail: [email protected] MS received 22 June 2020; revised 19 August 2020; accepted 20 August 2020
Abstract. The present work reports the synthesis and structural elucidation of six novel copper(II) complexes with 2-acetylpyridine semicarbazone (HL1) and 2-acetylpyridine N(4)-phenyl semicarbazone (HL2). In all compounds, the semicarbazone ligands were find tridentate with NNO-donor atoms. The single crystal X-ray diffraction analysis showed the influences of the different copper salt starting reagent in the crystal structures. A packing architectures analysis has been undertaken to delineate the role of relevant noncovalent interactions. The pp stacking interactions and hydrogen bonds were analyzed using the Hirshfeld surface and fingerprint plots. In addition, the compounds were also characterized by physicochemical and spectroscopic methods. Keywords. Noncovalent interactions; Crystal structures; Copper(II) complexes; Semicarbazone.
1. Introduction Polydentate ligands have been extensively investigated to obtain a wide range of compounds with structural diversity and distinct applications. In this context, the use of Schiff bases has been highlighted due to its stability and comprehensive structural versatility.1–3 The semicarbazones are important for their wide pharmacological profile and constitutive properties that are studied, not only for their chelating capacity when associated with metals in coordination compounds, but also for their comprehensive mechanisms of action. These mechanisms can be specifically predicted by structural description/analysis of the semicarbazones.4–7 Commonly the semicarbazones are shown in equilibrium in their keto and enol tautomeric forms, acting as a neutral ligand through the nitrogen atom from the imine group or the oxygen atom from the carbonyl group, or as a monoanionic ligand.8–10 The structural versatility of semicarbazones is further increased with many possible substituent groups, which most often include new sites of bonding, increasing the
possibilities of coordination with metal centers.2,11 Actually, the diverse structural possibilities of the semicarbazones and their coordination derivatives are responsible for the general applicability of these compounds, which is confirmed by their antiviral, antimicrobial, antiseptic, anti-convulsant, anti-inflammatory and anti-tumor efficacy.6,12–14 Additionally, copper complexes have shown satisfactory results regarding the biological activity spectrum.15–18 Considered one of the most abundant transition metal in the human body, copper is linked to important biological functio
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