Square Planar Pt(II) Ion as Electron Donor in Pnictogen Bonding Interactions

It has been proposed that late transition metals with low coordination numbers (square planar or linear) can act as nucleophiles and participate in sigma-hole interactions as electron donors. This is due to the existence, in this type of metal complexes, of a pair of electrons located at high energy d-orbitals (d(z)(2) or d(x)(2)-(2)(y)), which are adequate for interacting with antibonding sigma-orbitals [sigma*(X-Y)] where Y is usually an electron withdrawing element and X an element of the p-block. This type of d[M]& RARR;sigma*(X-Y) interaction has been reported for metals of groups 9-11 in oxidation states +1 and +2 (d(8) and d(10)) as electron donors and sigma-holes located in halogen and chalcogen atoms as electron acceptors. To our knowledge, it has not been described for sigma-holes located in pnictogen atoms. In this manuscript, evidence for the existence of pnictogen bonding involving the square planar Pt(II) metal as the electron donor and Sb as the electron acceptor is provided by using an X-ray structure retrieved from the Cambridge Structural Database (CSD) and theoretical calculations. In particular, the quantum theory of atoms in molecules (QTAIM), the noncovalent interaction plot (NCIPlot) and molecular electrostatic potential (MEP) methods were used. Moreover, to further confirm the nature of the Sb center dot center dot center dot Pt(II) contact, a recently developed method was used where the electron density (ED) and electrostatic potential (ESP) distribution were compared along the Sb & BULL;& BULL;& BULL;Pt(II) bond path.