A new
series of high-spin [CoII
2] complexes
[Co2(cpdp)(μ-O2CC6H5)] (1), [Co2(cpdp)(μ-o-O2CC6H4(OH))]·H2O (2), and [Co2(cpdp)(μ-p-O2CC6H4(OH))]·5H2O (3) of the carboxylate-affixed multidentate
ligand, N,N′-bis[2-carboxybenzomethyl]-N,N′-bis[2-pyridylmethyl]-1,3-diaminopropan-2-ol
(H3cpdp), have been synthesized and structurally characterized
[C6H5CO2
– = benzoate; o-C6H4(OH)CO2
– = ortho-hydroxybenzoate; p-C6H4(OH)CO2
– = para-hydroxybenzoate]. In methanol, complexes 1, 2, and 3 have been synthesized by carrying
out the reaction of H3cpdp with stoichiometric quantities
of Co(BF4)2·6H2O/C6H5CO2Na, Co(BF4)2·6H2O/o-C6H4(OH)CO2Na, and Co(BF4)2·6H2O/p-C6H4(OH)CO2Na respectively,
in the presence of NaOH at room temperature. Complexes 1–3 have been characterized by microanalysis, molar conductance, FTIR
and UV–vis, mass spectrometry, PXRD, thermogravimetric analysis,
single-crystal X-ray diffraction studies, and variable temperature
magnetic susceptibility measurements. In 1–3,
the nonbonded Co···Co separations are 3.4311(8), 3.4551(8),
and 3.4393(7) Å, respectively, and the Co(II) ions are doubly
bridged by one alkoxide group of the multidentate ligand and one benzoate/ortho-hydroxybenzoate/para-hydroxybenzoate
group. As disclosed by single-crystal X-ray analyses, all three complexes
assume distorted trigonal bipyramidal geometry around each cobalt
center under the N2O3 coordination environment
provided by the cpdp3– ligand and the ancillary
benzoate/ortho-hydroxybenzoate/para-hydroxybenzoate functionalities. The distorted trigonal bipyramidal
geometry is further authenticated by SHAPE analysis of the Co(II)
coordination sphere. Magnetic susceptibility data were recorded for 1–3 in the temperature range of 2–300 K, and
their analysis has disclosed the occurrence of antiferromagnetic interactions,
associated with the spin-orbit coupling effect. The nature and mechanism
of magnetic interactions are discussed on the basis of magneto-structural
parameters, and these are mainly correlated with the magnitude of
Co–Obridging alkoxide–Co angles. Moreover,
with the aim of reducing toxicity and irritation of free cobalt(II)
ion in the tissues, all three organo-chelated [CoII
2] complexes were evaluated as antibacterial agents against Staphylococcus aureus, SA96, which is known to cause
several life-threatening chronic infections and diseases. The antibacterial
studies revealed that all three complexes are significantly active
against this bacterial strain showing minimum inhibitory concentration
values in the range of 300–600 μg/mL. However, a comparative
assessment of their biological efficacies revealed that 2 and 3 exhibited higher antibacterial activity compared
to that of 1.
