A three-dimensional manganese(II) coordination polymer: synthesis, structure and catecholase activity

Abstract

A manganese-based coordination polymer, [Mn₂L₂(µ-MeOH)₂]_n (H₂L = 2-hydroxy-1-naphthaldehyde isonicotinoylhydrazone) was obtained by self-assembly of 2-hydroxy-1-naphthaldehyde isonicotinoylhydrazone and manganese(II) acetate. The coordination polymer was characterized by IR, EPR and UV–Vis spectroscopy. The single-crystal X-ray diffraction study reveals that the dibasic tridentate ligand (L²⁻) is bound via ONO donor sites to manganese(II). Two such [ML] fragments are connected by µ₂-bridged methanol (MeOH) to form a di-manganese species. The sixth site of each of the manganese is occupied by the pyridyl N atom of the isonicotinoyl group. This arrangement gives a polynuclear complex of the formula [Mn₂L₂(µ-MeOH)₂]_n. The coordination geometry of manganese is distorted octahedral. The X-band electron paramagnetic resonance (EPR) measurement of the complex at 77 K shows a six-line spectrum and a signal at the half field, with g = 4.88. The half-field signal indicates the dimeric nature of the complex in the solution state. The cyclic voltammetric measurement of the complex shows a reversible Mn^III/Mn^II redox couple. The complex catalyzes the conversion of 3,5-di-tert-butyl catechol to the corresponding o-quinone with a catalytic turnover rate of (k_cat) 27.22 h⁻¹.

Graphical Abstract

Keywords:

• Coordination polymer
• EPR spectra
• manganese
• catecholase activity
• cyclic voltammetry

Acknowledgements

The authors, PB and RJ, thank the Department of CSS, IACS Kolkata for facilitating X-ray single crystal data collection and PB thanks IIT(ISM) Dhanbad for financial support, National Taiwan University for XPS. The authors also acknowledge Dr. S.K. Padhi for cyclic voltammetry measurements and fruitful discussions.

Disclosure statement

No potential conflict of interest was reported by the author(s).