Stacking the Deck to Make Materials With Atypically Short Heterometallic d ⁸ M(II)···Au(III) Bonds

The first Pt II ···Au III metallophilic interaction is reported in K 4 [Pt(CN) 4 ][Au(CN) 4 ]Cl·6H 2 O, which consists of a 1D chain of stacking [Pt(CN) 4 ] 2− and [Au(CN) 4 ] − units bridged by potassium cations, with extremely short Pt II ···Au III distances of 3.0024(4) and 3.0057(4) Å at 80 K. The chloride ions and water molecules are bound to the potassium cation. Addition of KCl to the reaction mixture is necessary for the metallophilic Pt II ···Au III chain to assemble. The isostructural [Pd(CN) 4 ] 2− and [Ni(CN) 4 ] 2− analogs can be rationally synthesized in a similar manner, which feature the first Pd II ···Au III and Ni II ···Au III interactions, with the Ni II analog having the shortest metal‐metal distances of 2.968(3) and 2.978(3) Å. The bromide versions of all compounds were also synthesized by substituting KBr for KCl in the reaction mixture. 195 Pt solid‐state NMR of the title compound revealed highly anisotropic, axially symmetric magnetic shielding which resembles that found in systems with Pt II ···Pt II interactions, such as K 2 [Pt(CN) 4 ]·H 2 O. The Pd II and Pt II analogs are emissive, with λ max of 555 and 570 nm. Theoretical calculations indicate that the positive charge of the K + ions effectively neutralizes the electrostatic repulsion between the cyanometallates, resulting in significant metal‐based donor‐acceptor interactions. These novel d 8 ··· d 8 interactions provide a conceptual framework for the rational design of future metallophilic compounds.