Surface modifications of eight-electron palladium silver superatomic alloys

Atomically precise thiolate-protected coinage metal nanoclusters and their alloys are far more numerous than their selenium congeners, the synthesis of which remains extremely challenging. Herein, we report the synthesis of a series of atomically defined dithiophosph(in)ate protected eight-electron superatomic palladium silver nanoalloys [PdAg(20){S(2)PR(2)}(12)], 2a–c (where R = O(i)Pr, a; O(i)Bu, b; Ph, c) via ligand exchange and/or co-reduction methods. The ligand exchange reaction on [PdAg(20){S(2)P(O(n)Pr)(2)}(12)], 1, with [NH(4){Se(2)PR(2)}(12)] (where R = O(i)Pr, or O(n)Pr) leads to the formation of [PdAg(20){Se(2)P(O(i)Pr)(2)}(12)] (3) and [PdAg(20){Se(2)P(O(n)Pr)(2)}(12)] (4), respectively. Solid state structures of 2a, 2b, 3 and 4 unravel different PdAg(20) metal frameworks from their parent cluster, originating from the different distributions of the eight-capping silver(I) atoms around a Pd@Ag(12) centered icosahedron with C(2,) D(3,) T(h) and T(h) symmetries, respectively. Surprisingly ambient temperature crystallization of the reaction product 3 obtained by the ligand exchange reaction on 1 has resulted in the co-crystallization of two isomers in the unit cell with overall T (3a) and C(3) (3b) symmetries, respectively. To our knowledge, this is the first ever characterized isomeric pair among the selenolate-protected NCs. Density functional theory (DFT) studies further rationalize the preferred geometrical isomerism of the PdAg(20) core.