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E. Knittl, A. Abu-Hussen, W. Linert:
"Syntheses, characterization, and biological activity of novel mono- and binuclear transition metal complexes with a hydrazone Schiff base derived from a coumarin derivative and oxalyldihydrazine";
Monatshefte für Chemie (invited), 149 (2018), 431 - 443.

A hydrazone Schiff base ligand was synthesized
by the condensation of 3-formyl-4-hydroxycoumarin and
oxalyldihydrazide in the molar ratio 2:1. The Schiff base
ligand acts as a mono-, bi-, tri- or even tetradentate ligand
with metal cations in the molar ratios 1:1 or 2:1 (M:L) to
yield either mono- or binuclear complexes as keto or enol
isomers, where M = Co(II), Ni(II), Cu(II), VO(IV), and
Fe(III). The ligand and its metal complexes were characterized
by elemental analyses, IR, 1H NMR, mass, and
UV-Vis spectroscopy. Furthermore, the magnetic moments
were calculated from the measured electric conductivities
of the complexes. According to the received data, the
dihydrazone ligand contains one or two units of ONO
domains and can bind to the metal ions via the azomethine
nitrogen, the carbonyl oxygen atoms, and/or the phenolic
oxygen atoms. Electronic spectra and the magnetic
moments of all complexes show that the complexes´
geometries are either octahedral, tetrahedral, square planar,
or square pyramidal. Cyclic voltammograms of the
mononuclear Co(II) and Ni(II) complexes show quasi-reversible
peaks. Tests against two pathogenic bacteria as
Gram-positive and Gram-negative bacteria for both, the
Schiff base ligand and its metal complexes were carried
out. In addition, also one kind of fungi was tested. The
synthesized complexes demonstrate mild antibacterial and
antifungal activities against these organisms.

3-Formyl-4-hydroxycoumarin derivative

http://dx.doi.org/10.1007/s00706-017-2075-9