Equatorial π-stacking interactions in diruthenium (II,III) tetracarboxylate complexes containing extended π-systems

• Three [Ru2(μ-O2CR)4(solvent)2]+ complexes with extended π-systems were synthesized and structurally characterized.
• Two of these complexes showed extensive π-stacking interactions in two dimensions.
• No interactions are seen when π-system is perpendicular to carboxylate (OCO) plane.

The synthesis of three new valent-averaged tetracarboxylatodiruthenium (II,III) complexes, [Ru2(1-naphthylacetate)4(H2O)2](PF6)⋅4THF, 1⋅4THF, [Ru2(2-naphthoate)4(THF)2](PF6)⋅3THF, 2⋅3THF, and [Ru2(coumarin-3-carboxylate)4(MeOH)2](PF6)⋅MeOH⋅H2O, 3⋅MeOH⋅H2O, was accomplished using a well documented carboxylate exchange reaction. All three complexes were thoroughly characterized using infrared and UV–Vis spectroscopies, elemental analysis and X-ray diffraction. Due to the extended π-systems present, two of the complexes, 2⋅3THF and 3⋅MeOH⋅H2O, display extensive π-stacking in two dimensions, with similar interactions notably absent in 1⋅4THF due to the perpendicular orientation of the naphthyl rings. Modest H-bonding is seen in complexes 1⋅4THF and 3⋅MeOH⋅H2O. As these types of complexes are noted secondary building units (SBU’s) in the construction of metal–organic frameworks (MOF’s), the significance of these interactions in stabilizing even larger, supramolecular structures, are noted.