Monomeric complexes of manganese(II) with tetradentate ligands: isolation of cis-diaquamanganese(II) and cis-dichloromanganese(II) species

Abstract

The synthesis and characterization of the monomeric complexes cis-diaqua( N, N′-bis(2-methylpyrazyl)ethane-1,2-diamine)manganese(II) perchlorate monohydrate ( 1), or cis-[Mn(bispyzen)- (H 2O) 2](ClO 4) 2·H 2O, and cis-dichloro( N, N-bis((6-methylpyrid-2-yl)methyl)- N-2-pyridylmethylamine) manganese(II) ( 2) are reported. The diaqua complex crystallizes in the monoclinic space group P2 1/ c with four molecules in a cell of dimensions a=13.394(4), b=9.778(3), c=17.434(7) Å, β=103.15(3)°. The structure has been refined to an R factor of 0.0485 based on 3857 independent intensities. The OMnO bond angle in the complex is 93.9(1)°, and the MnO bond lengths are 2.137(3) and 2.158(3) Å. There is extensive hydrogen bonding in the crystals. The dichloro complex crystallizes in the monoclinic space group P2 1/ n with four molecules in a cell of dimensions a=8.993(2), b=28.717(7), c=9.053(2) Å. β=118.84(1)°. The structure has been refined to an R factor of 0.0370 based on 3276 independent intensities. The ClMnCl bond angle in the complex is 99.4(1)°, and the MnCl bond lengths are 2.402(1) and 2.467(1) Å. The axial MnN bond lengths of 2.423(2) and 2.456(3) Å are much longer than the equatorial MnN distances of 2.285(3) and 2.329(3) Å; this observed elongation of the axial bonds is presumably due to the steric crowding caused by the presence of the 6-methyl groups on the axial pyridine rings. The dichloro complex shows a quasi-reversible redox wave at 0.80 V versus Ag/AgCl corresponding to the Mn(II)↔Mn(III) couple.