Abstract
Four manganese(II) bromide coordination complexes have been prepared with four pyridine N-oxides, viz. pyridine N-oxide (PNO), 2-methyl-pyridine N-oxide (2MePNO), 3-methyl-pyridine N-oxide (3MePNO), and 4-methyl-pyridine N-oxide (4MePNO). The compounds are bis-(μ-pyridine N-oxide)bis-[aqua-dibromido-(pyridine N-oxide)manganese(II)], [Mn2Br4(C5H5NO)4(H2O)2] (I), bis-(μ-2-methyl-pyridine N-oxide)bis-[di-aqua-dibromido-manganese(II)]-2-methyl-pyridine N-oxide (1/2), [Mn2Br4(C6H7NO)2(H2O)4]·2C6H7NO (II), bis-(μ-3-methyl-pyridine N-oxide)bis-[aqua-dibromido-(3-methyl-pyridine N-oxide)manganese(II)], [Mn2Br4(C6H7NO)4(H2O)2] (III), and bis-(μ-4-methyl-pyridine N-oxide)bis-[di-bromido-methanol(4-methyl-pyridine N-oxide)manganese(II)], [Mn2Br4(C6H7NO)4(CH3OH)2] (IV). All the compounds have one unique MnII atom and form a dimeric complex that contains two MnII atoms related by a crystallographic inversion center. Pseudo-octa-hedral 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 mol-ecule of solvation. Compounds I, III and IV exhibit the same arrangement of mol-ecules around each manganese atom, ligated by two bromide ions, oxygen atoms of two PNO ligands and one solvent mol-ecule, whereas in compound II each manganese atom is ligated by two bromide ions, one O atom of a PNO ligand and two water mol-ecules with a second PNO mol-ecule inter-acting with the complex via hydrogen bonding through the bound water mol-ecules. 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.
Highlights
N-oxides have interesting binding modes that facilitate the growth of unique coordination structures
We report the synthesis and solid-state structures of four pyridine N-oxide manganese(II) dimeric complexes, using pyridine N-oxide (PNO) and its mono-methyl-substituted forms, 2-methylpyridine N-oxide (2MePNO), 3-methylpyridine N-oxide (3MePNO), and 4-methylpyridine N-oxide (4MePNO). This was done to study the impact of substitution of the pyridine on the two- and three-dimensional solid-state structures, and to compare them to previous structures in which the bromide ions are replaced with chloride ions
General structural details The pyridine N-oxide complexes form dimers consisting of two MnII atoms related by an inversion center; the dimer contains a six-coordinate metal center at each MnII ion with four donor oxygen atoms and two bromides
Summary
N-oxides have interesting binding modes that facilitate the growth of unique coordination structures Their utility to facilitate organic oxotransfer reactions has been well documented over the years (see, for example, Eppenson, 2003). A recent report shows the utility of pyridine N-oxide to facilitate coordination polymer formation with both zinc(II) and manganese(II) metal ions with a single bifunctional ligand containing an acetate and N-oxide moiety (Ren et al, 2018) These have been reported by us (Lynch et al, 2018; Kang et al, 2017) and others (Sarma et al, 2008, 2009; Sarma & Baruah, 2011). This was done to study the impact of substitution of the pyridine on the two- and three-dimensional solid-state structures, and to compare them to previous structures in which the bromide ions are replaced with chloride ions
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