Argento– aurophilic bonding in organosulfur complexes. The molecular and electronic structures of the heterobimetallic complex AgAu(MTP) 2

Abstract

The heterobimetallic complex AgAu(MTP) 2, ( 1), was obtained from the reaction of PPN[Au(MTP) 2] with AgNO 3 (MTP=diphenylmethylenethiophosphinate; PPN=bis(triphenyl-phosphoranylidene)ammonium). Compound 1 was found to be isomorphous with but not isostructural to the previously reported compounds Au 2(MTP) 2, ( 2) and Ag 2(MTP) 2, ( 3). Surprisingly, 1 has a very short intramolecular AgAu distance (2.912 Å), which is much shorter than the intramolecular metal–metal distances in 2 and 3 (∼3.0 Å in both). The three compounds form extended one-dimensional chain structures in the solid state. The intermolecular interactions in 1 were found to be AgAu interactions (3.635 Å), as opposed to AuAu and AgAg interactions. Density-functional theory (DFT) calculations were used to study the stability of the geometrical isomers with different coordination modes of the MTP ligand in models of 1– 3. Isomers with AgC bonds were found much higher in energy than those with AuC bonds, which explains the stability of 1 and 2, which have AuC bonds, relative to 3, which has two AgC bonds. Dilute solutions of the three compounds showed virtually identical absorption spectra in which the lowest-energy band is due to a π–π* intraligand transition. The electronic spectra for concentrated solutions and the solid state show lower energy bands due to intermolecular interactions. The relative energies of the absorption edge followed the order Au 2≪AgAu<Ag 2. DFT calculations demonstrate that monomer models cannot describe this trend. However, DFT calculations for dimer and trimer models of the three compounds give excellent agreement with the experimental results, as the HOMO–LUMO gap follows the same order as the absorption edge. The importance of intermolecular metal–metal interactions is further manifested by the presence of emission bands in the visible region for the three compounds. Crystal data for AgAu(CH 2P(S)Ph 2) 2: monoclinic, space group C2/ c; Z=8; a=24.384(2) Å; b=6.5472(6) Å; c=16.4884(18) Å; β=113.356(5)°.