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

A manganese-based coordination polymer, [Mn2L2(mu-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 mu(2)-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(mu-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).