Predicting Supramolecular Connectivity of Metal-Containing Solid-State Assemblies using Calculated Molecular Electrostatic Potential Surfaces

We demonstrated that the primary supramolecular features of metal-based solid-state systems can be reliably predicted based solely on the relative strengths of competing hydrogen-bond acceptor sites. The predictive protocol utilizes a simple electrostatic view of the hydrogen bond and ranks the multiple acceptor sites according to calculated molecular electrostatic potential (MEP) surface values. The MEP was calculated for competing acceptors on 12 zero-dimensional (0-D) 2,4-pentanedionate (acac)-based complexes (Ni(II), Co(II), Cu(II)), equipped with the lactam moiety, and the structural outcome was successfully predicted in 10 of 12 compounds by comparing the MEP difference between two acceptors, namely, the lactam and acac-based oxygen atoms. The two acceptor sites displayed structural selectivity as long as there was a substantial difference (Delta E > Delta E-cutoff) between their relative hydrogen-bond acceptor capabilities. In the remaining two cases, the expected coordination geometry around the metal center did not materialize, which meant that a prediction of the supramolecular details could not be done. The working cutoff value (Delta(Ecutoff) approximate to 30 kJ/mol) proved to be a valid and decisive criterion for predicting the supramolecular connectivity in these 0-D systems. The results further indicate that the Delta E-cutoff is likely to be primarily dependent on the supramolecular functionality itself rather than on external "packing forces".