Tuning of coordination geometry via cooperation of inter- and intramolecular hydrogen bonds in bis(benzoylacetonato)manganese(II) adducts with pyridine derivatives

In order to study the effects of intramolecular hydrogen bonding on coordination geometry of a relatively rigid octahedral system, eight coordination compounds derived from bis(benzoylacetonato)manganese(II) and seven pyridine derivatives (three of them o-aminopyridines) were prepared. Four compounds in which intramolecular hydrogen bonds could not be formed are centrosymmetric with similar lengths of equivalent Mn-L bonds. When o-aminopyridines were employed, an intramolecular hydrogen bond was always formed. In the case of two compounds this led only to minor changes of molecular geometry, while in the other two the coordination complex was changed from a centrosymmetric all-trans configuration to a molecule with cis-configuration of pyridine ligands and of pseudo C-2 symmetry. This change was found to affect not only the bond lengths of the coordination molecule, but also to allow for a much better crystal packing as it enabled a closer hydrogen bonding contact between adjacent molecules.