Metal–metal interactions in linear tri-, penta-, hepta-, and nona-nuclear ruthenium string complexes

Density functional theory (DFT) methodology was used to examine the structural properties of linear metal string complexes: [Ru 3 (dpa) 4 X 2 ] (X = Cl − , CN − , NCS − , dpa = dipyridylamine − ), [Ru 5 (tpda) 4 Cl 2 ], and hypothetical, not yet synthesized complexes [Ru 7 (tpta) 4 Cl 2 ] and [Ru 9 (ppta) 4 Cl 2 ] (tpda = tri-α-pyridyldiamine 2− , tpta = tetra-α-pyridyltriamine 3− , ppta = penta-α-pyridyltetraamine 4− ). Our specific focus was on the two longest structures and on comparison of the string complexes and unsupported ruthenium backboned chain complexes, which have weaker ruthenium–ruthenium interactions. The electronic structures were studied with the aid of visualized frontier molecular orbitals, and Bader’s quantum theory of atoms in molecules (QTAIM) was used to study the interactions between ruthenium atoms. The electron density was found to be highest and distributed most evenly between the ruthenium atoms in the hypothetical [Ru 7 (tpta) 4 Cl 2 ] and [Ru 9 (ppta) 4 Cl 2 ] string complexes.