Evidence for d orbital aromaticity in square planar coinage metal clusters.

摘要: Quantitative evidence for the existence of aromaticity involving d orbitals transition metals is provided first time. The doubly bridged square planar (D(4)(h)()) coinage metal clusters (M(4)Li(2), M = Cu (1), Ag (2), and Au (3)) are characterized as aromatic by their substantial nucleus independent chemical shifts (NICS) values in centers (-14.5, -14.1, -18.6, respectively). Nevertheless, participation p bonding (and cyclic electron delocalization) 1-3 negligible. Instead, these benefit strongly from delocalization to some extent s orbitals. same conclusion applies Tsipis Tsipis' H-bridged D(4)(h)() Cu(4)H(4) ring (4). Canonical MO-NICS analysis structures shows total diatropic orbital contributions NICS be substantial, although individual five sets filled vary. Cu(4)Li(2) also indicated its atomization energy, 243.2 kcal/mol, which larger than Boldyrev's (sigma pi) Al(4)Li(2) (215.9 kcal/mol).