Mapping of Solvent Mediated Molecular Self-Assembly of Fe(III) Discrete Compounds: Exploring their Magnetic Behaviour and Phosphatase Like Activity

Two newly synthesized Fe(III) based complexes, [Fe4L2(mu(3)-O)(2)(Cl)(2)(MeOH)(4)(H2O)(4) ](ClO4)(2) center dot 4H(2)O center dot MeOH (1) and [Fe2L3]center dot 4DMF (2) were isolated in solid crystalline form using the reaction of iron(III) perchlorate with the ligand H2L (H2L = 6,6'-( (1E,1'E)-hydrazine-1,2-diylidenebis (methanylylidene) )bis (2-m ethoxyphenol) . (DMF= N,N-dimethylformamide, MeOH = methanol). Compound 1 was self-assembled in MeOH, but when the solvent was changed to DMF, compound 2 was harvested. Furthermore, compound 1 was converted to compound 2 just by dissolving compound 1 in DMF. Sequential self-assembly and conversion of compound 1 to 2 were monitored by UV-vis spectroscopy and ESI-Mass spectroscopy in solution phase. Single crystal X-ray analysis showed that compound 1 has mu(3) -oxo bridged tetranuclear structure whereas compound 2 has puckered dinuclear structure. Magnetic studies indeed revealed frustrated magnetic spin for compound 1 whereas antiferromagnetic interaction was observed for compound 2. The spectrophotometrical investigation on their phosphatase like activity revealed remarkable hydrolytic efficiency for both the complexes. Michaelis-Menten-derived kinetic parameters suggest the competitiveness of the rate of P-O bond fission employing the phosphomonoester (4-nitrophenyl)phosphate (PNPP) in 97.5% DMF is 1 > 2, and the k(cat) value lies in the range 28.95-38.43 s(-1) at 298 K. Computational calculations have verified the higher catalytic activity of compounds 1 over 2 attributed to the large number of labile groups attached to the metal centers.