Three new tetranuclear phenoxy-bridged metal(II) complexes: Synthesis, structural variation, cryomagnetic properties, DFT study and antiprolifirative properties

Abstract

Three tetranuclear phenoxy-bridged copper(II) and zinc(II) complexes containing acetic acid (2-hydroxy-3-methoxy-benzylidene)-hydrazide (HL) of formulae [Cu4(HL)4]·4ClO4·2H2O 1, [Cu4(L)4]·4H2O 2 and [Zn4(L)4]·4H2O 3 are synthesized and characterized using various physico-chemical methods. Their X-ray structures reveal that copper(II) complexes 1 and 2 contain distorted Cu4O4 cubane core of 4 + 2 type. Zinc complex 3 is open cubane like Zn4O4 core frame work. The coordination sphere in copper(II) complexes 1 and 2 can be described as a distorted octahedral geometry whereas zinc(II) complex 3 has distorted square pyramidal geometry. The variable temperature magnetic susceptibility measurements on tetranuclear cubane like copper(II) complexes in the range 2–300 K indicate antiferromagnetic exchange coupling between copper(II) centers. The best fit data gave J1 = −82.4 (4) cm−1, J2 = 22 (2) cm−1 and g = 1.95 (1) (R2 = 0.99996) whereas for 2 it gave J1 = −86 (1) cm−1, J2 = 5 (2) cm−1 and g = 2.074 (7) (R2 = 0.9998). The nature of super exchange pathway in copper(II) complexes (1 and 2) is discussed on the basis of structural, magnetic and molecular orbital considerations. DFT calculations are performed in order to obtain their molecular orbitals and energies using their crystallographic parameters. The inhibitory effects of the complexes on cell population growth on IMR 32 (neuroblastoma), MCF 7 (breast cancer), HepG2 (hepatocellular carcinoma), L132 (lung cells) cell lines were determined by MTT assay. The complex [Cu4(L)4]·4H2O 2 showed a significant anti-proliferative effect. The expression levels of Bax (pro-apoptotic), Bcl2 (anti-apoptotic), Caspase 9 and p53 genes were also studied, wherein genes of interest showed moderate down regulation after treatment with all the complexes.