Abstract
Structural analysis of (acetato-κ2O,O')(methanol-κO)[tris-(pyridin-2-ylmeth-yl)amine-κ4N,N',N'',N''']manganese(II) tetraphenyl-borate, [Mn(C2H3O2)(C18H18N4)(CH3OH)](C24H20B) or [Mn(TMPA)(Ac)(CH3OH)]BPh4 [TMPA = tris-(pyridin-2-ylmeth-yl)amine, Ac = acetate, BPh4 = tetra-phenyl-borate] by single-crystal X-ray diffraction reveals a complex cation with tetra-dentate coordination of the tripodal TMPA ligand, bidentate coordination of the Ac ligand and monodentate coordination of the methanol ligand to a single MnII center, balanced in charge by the presence of a tetra-phenyl-borate anion. The MnII complex has a distorted penta-gonal-bipyramidal geometry, in which the central amine nitro-gen and two pyridyl N atoms of the TMPA ligand, and two oxygen atoms of the acetate ligand occupy positions in the penta-gonal plane, while the third pyridyl nitro-gen of TMPA and the oxygen from the methanol ligand occupy the axial positions. Within the complex, the acetate O atoms participate in weak C-H⋯O hydrogen-bonding inter-actions with neighboring pyridyl moieties. In the crystal, complexes form dimers by pairs of O-H⋯O hydrogen bonds between the coordinated methanol of one complex and an acetate oxygen of the other, and weak π-stacking inter-actions between pyridine rings. Separate dimers then undergo additional π-stacking inter-actions between the pyridine rings of one moiety and either the pyridine or phenyl rings of another moiety that further stabilize the crystal.
Highlights
Structural analysis of(methanol-O)[tris(pyridin-2-ylmethyl)amine-4N,N0,N00,N000]manganese(II) tetraphenylborate, [Mn(C2H3O2)(C18H18N4)(CH3OH)](C24H20B) or [Mn(TMPA)(Ac)(CH3OH)]BPh4 [TMPA = tris(pyridin-2-ylmethyl)amine, Ac = acetate, BPh4 = tetraphenylborate] by single-crystal X-ray diffraction reveals a complex cation with tetradentate coordination of the tripodal TMPA ligand, bidentate coordination of the Ac ligand and monodentate coordination of the methanol ligand to a single MnII center, balanced in charge by the presence of a tetraphenylborate anion
The acetate O atoms participate in weak C—HÁ Á ÁO hydrogen-bonding interactions with neighboring pyridyl moieties
The remaining two positions in the pentagonal plane are completed by the bidentate coordination of the acetate ligand (O2 and O3), while the final axial position is occupied by O1 of the methanol ligand
Summary
A variety of manganese(II/III) complexes have been studied as structural and functional mimics of superoxide dismutase (SOD) enzymes (Batinic-Haberle et al, 2010, 2014; Iranzo, 2011; Bani & Bencini, 2012; Miriyala et al, 2012; Policar, 2016) The efficacy of these mimics is reliant on their stability in aqueous solution, retention of open or substitutional coordination sites on the manganese ion, and MnIII/MnII redox potential lying in the narrow range of 0.2–0.4 V versus a normal hydrogen electrode (Iranzo, 2011; Policar, 2016). The bond between the manganese(II) ion and the central TMPA nitrogen, Mn1—N2 is considerably long at 2.4092 (13) A This elongation has been observed in other manganese(II) complexes with tripodal, tetradentate ligands (Deroche et al, 1996; Wu et al, 2010). The other Mn—O and Mn—N bonds fall into the range 2.2–2.3 A , which is typical of manganese(II) complexes (Deroche et al, 1996; Policar et al, 2001; Lessa et al, 2007; Dees et al, 2007; Wu et al, 2010; Lieb et al, 2012)
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