Crystal Structures of Copper(II) Complexes of Some 2-Methyl-8-quinolinols andImplications for their Antifungal Activity

Abstract

A hypothesis that the geometry of a potential fungicide must be consistent with that of the pores of the fungal spore wall in order to penetrate it and be toxic has been developed. Certain bis(8-quinolinolato)copper(II) complexes seemed to contradict this. To resolve this issue, structures of bis(7-¯uoro-8-quinolinolato)copper(II) (1), bis(2-methyl-8-quinolinolato)copper(II) (2), and bis(2-methyl-7-nitro-8-quinolinolato)copper(II) (3) were solved. The ligands of 1 are square planar with copper at the center of symmetry. In 2 and 3 the methyl group at C2 interacts with the other 8-quinolinol ligand, producing a signi®cant distortion of the square planar geometry which causes a rotation about the N-Cu-N axis and allows the molecules to be polar, more compact, and manifest their toxicity. Bis(7-Nitro-8-quinolinolato)copper(II) is square planar and nontoxic.Kristallstrukturen der Kupfer(II)-Komplexe einiger 2-Methyl-8-chinolinole und ihre Bedeutung fu È r deren fungizide Eigenschaften Zusammenfassung. Einer Hypothese zufolge muû die Geometrie eines potentiellen Fungizids mit jener der Poren in der Sporenwand der Pilze u Èbereinstimen, um sie durchdringen und seine fungizide Wirkung entfalten zu ko Ènnen. Die Eigenschaften gewisser Bis(8-chinolinolato)kupfer(II)-Komplexe schienen dem zu widersprechen. Zur Au¯o Èsung dieser Diskrepanz wurden die Kristallstrukturen von Bis(7-¯uoro-8-chinolinolato)kupfer(II) (1), Bis(2-methyl-8-chinolinolato)kupfer(II) (2) und Bis(2-methyl-7-nitro-8-chinolinolato)kupfer(II) (3) bestimmt. Die Liganden von 1 sind quadratisch-planar mit Kupfer im Symmetriezentrum. In 2 und 3 tritt eine sterische Wechselwirkung der Methylgruppe an C2 mit dem jeweils anderen 8-Chinolinol-Liganden auf, die zu einer deutlichen Verzerrung der quadratisch-planaren Struktur fu Èhrt. Die dadurch auftretende Rotation um die N-Cu-N-Achse macht das Moleku Èl polarer, kompakter und toxisch. Bis(7-nitro-8-chinolinolato)kupfer(II) ist quadratischplanar und ungiftig.

Solution Chemistry of Copper(II) Binding to Substituted 8-Hydroxyquinolines

“…8HQs with substituents in the 2-position show altered Cu­(II) coordination environments, likely because the 8HQ ligands and the Cu­(II) are not all coplanar; although less likely, it could also be because the substituents preclude the formation of Cu­(II)-bis-complexes through steric or other effects. Distortion of the planar bis complexes observed with 2-position substitution appears to agree with crystallographically determined structures of various 2-substituted 8HQ derivatives that also show 4-coordinate Cu­(II) coordination distorted from the pseudo square planar-like geometry of 2-H 8HQs (e.g., CSDS entries KAFTOA, KAFTUG, QAFNOD, QAFWIG, QUJTAR, and YIGROW). However, not all crystal structures of 2-position-substituted 8HQ complexes with Cu­(II) show a significantly distorted 4-coordinate geometry.…”

Structures of the Copper and Zinc Complexes of PBT2, a Chelating Agent Evaluated as Potential Drug for Neurodegenerative Diseases

“…It should be emphasized that the same solid‐state structure [Cu II (PBT2) 2 ] was obtained when starting from different CuCl 2 /PBT2 molar ratios and various organic solvent combinations (DMF/CH 2 Cl 2 , DMF/acetone, DMF/acetonitrile, methanol/CH 2 Cl 2 ). Such a significant distortion of the usually preferred octahedral/square‐planar geometries of Cu II has previously been reported for copper complexes of 2‐substituted 8‐hydroxyquinoline derivatives …”

Synthesis, Structure Characterization and Antitumor Activity Study of a New Iron(III) Complex of 5-Nitro-8-hydroxylquinoline (HNOQ)

“…Although quite some metal complexes of HNOQ have been reported, 20,21) their biological activities, especially antitumor activities, have not yet been fully explored. 22,23) As to the iron complexes of HNOQ, only their coordination chemistry was studied in the early years.…”