Electronic stabilization of trigonal bipyramidal clusters: The role of the Sn(II) Ions in [Pt5(CO)5{Cl2Sn(?-OR) SnCl2}3]3- (R = H, Me, Et, iPr)

The new [Pt5(CO)5{Cl2Sn(?-OR)SnCl2}3]3- (R = H, Me, Et, iPr; 1-4) clusters contain trigonal bipyramidal (TBP) Pt5(CO)5 cores, as certified by the X-ray structures of [Na(CH3CN)5][NBu4]2[1]·2CH3CN and [PPh4]3[4]·3CH3COCH3. The TBP geometry, which is rare for group 10 metals, is supported by an unprecedented interpenetration with a nonbonded trigonal prism of tin atoms. By capping all the Pt3 faces, the Sn(II) lone pairs account for both Sn-Pt and Pt-Pt bonding, as indicated by DFT and topological wave function studies. In the TBP interactions, the metals use their vacant s and p orbitals using the electrons provided by Sn atoms, hence mimicking the electronic picture of main group analogues, which obey the Wade's rule. Other metal TBP clusters with the same total electron count (TEC) of 72 are different because the skeletal bonding is largely contributed by d-d interactions (e.g., [Os5(CO)14(PR3)(?-H)n]n-2, n = 0, 1, 2). In 1-4, fully occupied d shells at the Ptax atoms exert a residual nucleophilicity toward the adjacent main group Sn(II) ions permitting their hypervalency through unsual metal donation.