The Influence of the Axial Ligand on the Solid-State Structures of Pentacoordinate Manganese Tetraphenylporphyrin Complexes

Abstract

The crystal structures of Mn(tpp)(NCO), Mn(tpp)(CH₃CO₂).0·5C₇H₈, Mn(tpp)(NCS).0·5C₇H₈, Mn(tpp)(Br).C₇H₈, Mn(tpp)(I).C₇H₈ and the previously reported structures Mn(tpp)(Cl).(CH₃)₂CO, Mn(tpp)(Cl).C₇H₈, Mn(tpp)(NO₂).C₆H₆, Mn(tpp)(NO₃).2C₆H₆, Mn(tpp)(OSO₃H), Mn(tpp)(H₂O).-SO₃CF₃ and Mn(tpp)(CN).CHCl₃ are used to assess the role of the axial anion in the crystal packing of pentacoordinate manganese tetraphenylporphyrin complexes. A comparison of the packing strategies adopted by the toluene solvates suggests that the axial anion can sterically determine the lattice packing motif. Amongst the structures examined, there appears to be a hierarchy of packing strategies led by the elegant ‘slot together’ assembly pattern underpinning the Mn(tpp)(Br).C₇H₈ and Mn(tpp)(Cl).C₇H₈ lattices. The metrical parameters that have been used to assess intercomplex interactions in the solid state are shown to be crystal packing sensitive. This is clearly evident in the structure of Mn(tpp)(I).C₇H₈ which has two crystallographically independent molecules. The displacement of the metal ion from the porphyrin core is determined by the axial ligand field; however, this otherwise intrinsic property is also crystal packing dependent. That is, the iodo ligand field itself is modulated by crystal packing interactions. The isomorphous Mn(tpp)(CH₃CO₂).0·5C₇H₈ and Mn(tpp)(NCS).0·5C₇H₈ structures, which also have two crystallographically independent molecules, indicate that the axial ligand field strength can influence intercomplex interactions in the solid state, by moderating charge donation from the porphyrin to the metal.