MONOMERIC COMPLEXES OF MANGANESE(II) WITH TETRADENTATE LIGANDS - ISOLATION OF CIS-DIAQUAMANGANESE(II) AND CIS-DICHLOROMANGANESE(II) SPECIES

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)-(H2O)2](ClO4)2.H2), 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) angstrom, beta = 103.15(3)-degrees. 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)-degrees, and the Mn-O bond lengths are 2.137(3) and 2.158(3) angstrom. 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) angstrom, beta = 118.84(1)-degrees. 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)-degrees, and the Mn-Cl bond lengths are 2.402(1) and 2.467(1) angstrom. The axial Mn-N bond lengths of 2.423(2) and 2.456(3) angstrom are much longer than the equatorial Mn-N distances of 2.285(3) and 2.329(3) angstrom; 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) less-than-- --greater-than Mn(III) couple.