Crystal structures of four dimeric manganese(II) bromide coordination complexes with various derivatives of pyridine N-oxide

Four manganese(II) bromide coordination complexes have been prepared with four pyridine N-oxides, viz. pyridine N-oxide (PNO), 2-methylpyridine N-oxide (2MePNO), 3-methylpyridine N-oxide (3MePNO), and 4-methylpyridine N-oxide (4MePNO). The compounds are bis(μ-pyridine N-oxide)bis[aquadibromido(pyridine N-oxide)manganese(II)], [Mn₂Br₄(C₅H₅NO)₄(H₂O)₂] (I), bis(μ-2-methylpyridine N-oxide)bis[diaquadibromidomanganese(II)]-2-methylpyridine N-oxide (1/2), [Mn₂Br₄(C₆H₇NO)₂(H₂O)₄]∙2C₆H₇NO (II), bis(μ-3-methylpyridine N-oxide)bis[aquadibromido(3-methylpyridine N-oxide)manganese(II)], [Mn₂Br₄(C₆H₇NO)₄(H₂O)₂] (III), and bis(μ-4-methyl-pyridine N-oxide)bis[dibromidomethanol(4-methylpyridine N-oxide)manganese(II)], [Mn₂Br₄(C₆H₇NO)₄(CH₃OH)₂] (IV). All the compounds have one unique Mn^II atom and form a dimeric complex that contains two Mn^II atoms related by a crystallographic inversion center. Pseudo-octahedral six-coordinate manganese(II) centers are found in all four compounds. All four compounds form dimers of Mn atoms bridged by the oxygen atom of the PNO ligand. Compounds I, II and III exhibit a bound water of solvation, whereas compound IV contains a bound methanol molecule of solvation. Compounds I, III and IV exhibit the same arrangement of molecules around each manganese atom, ligated by two bromide ions, oxygen atoms of two PNO ligands and one solvent molecule, whereas in compound II each manganese atom is ligated by two bromide ions, one O atom of a PNO ligand and two water molecules with a second PNO molecule interacting with the complex via hydrogen bonding through the bound water molecules. All of the compounds form extended hydrogen-bonding networks, and compounds I, II, and IV exhibit offset π- stacking between PNO ligands of neighboring dimers.