Influence of d-orbital occupancy on ligand conformation and crystal packing in a series of mononuclear transition metal complexes

A series of mononuclear metal complexes were synthesised incorporating either Mn(II), Co(II), Ni(II), Cu(II), or Zn(II) metal ions in conjunction with a newly reported ligand, tris((((1-phenyl-1H-imidazol-4-yl)methylene)amino)ethyl)ethane-1,2-diamine (L). Each of the presently reported metal complexes was characterised in solution and in the solid state. Single-crystal X-ray diffraction studies were used to examine how changes in the coordination sphere (and d-orbital occupancy) of each metal ion modify the crystal packing motif, ligand torsion, and the spatial orientation of pendant phenyl groups in the metal complexes. The results presented within demonstrated that the complexation of metal ions bearing different d-orbital occupancies generated separate packing motifs except for the isostructural Co(II) and Zn(II) complexes. These differing motifs gave rise to small variations in the octahedral distortion parameters, ligand arm torsion, and the positions of the pendant phenyl groups across the series. These findings illustrate how structural and electronic differences, arising from the choice of metal ion and the atomic composition of pendant groups, influence ligand conformation and crystal packing within mononuclear systems. Such simple mononuclear complexes may therefore provide a foundation upon which larger, more elaborate metallosupramolecular assemblies can be rationally constructed.