Solid state and solution structures of complexes of the type λ-β₂-[Co(R,R-picchxn)(R-aa)]²⁺ [picchxn = N,N¹-di(2-picolyl)-1,2-diaminocyclohexane; aa = aromatic aminoacidate

The ternary complexes Λ-β₂-[Co(R,R-picchxn)(R-phe)](PF₆) ₂ and Λ-β₂-[Co(R,R-picchxn)(R-tyr)](ClO₄) ₂· H₂O have been synthesized and characterized using X-ray diffraction and high-resolution NMR methods (picchxn = N,N¹-di(2-pyridyl)-1,2-diaminocyclohexane; phe = the anion of phenylalanine; tyr = the anion of tyrosine). In the solid state, the aromatic ring of the aminoacidate adopts a π-stacked conformation with one of the pyridyl rings of the tetradentate ligand in an intramolecular fashion for both complexes. In addition, a weak secondary intramolecular NH-π interaction is present between one of the amino protons and the aromatic ring of the aminoacidate in each complex. Noncovalent interactions also influence the crystal packing of these species, with the complexes cations linked by intermolecular π-π and CH-π interactions in addition to a conventional hydrogen bonding network. NMR studies show that the solid state molecular conformations of these complexes also dominate in solution, demonstrating the significance of the discriminatory noncovalent interactions described in biochemical systems.