Synthesis and third-order nonlinear optical properties of Mo3μ3-Sμ2-S234clusters with maleonitriledithiolate, oxalate and thiocyanate ligands

Substitution of the bromine ligands in n-Bu4N2Mo3S7Br61 by bidentate ligands such as maleonitriledithiolate mnt or oxalate (ox) affords the trinuclear clusters Mo3S7mnt32−22− and Mo3S7ox32−32− in moderate yields. The structures of clusters 22−and 32−have been determined by single-crystal X-ray diffraction as their tetrabutylammonium salts. Cluster 2forms dimers by interaction of one sulfur atom of the mnt ligand with the anionic binding site of the cluster anion. The structure of 3reveals the presence of aggregates between the anionic cluster and a Br−ion. The ESI-MS indicate that these cluster–bromine adducts are also present in solution. Electrochemical studies on complexes 1–3show two irreversible waves associated with reductive cleavage of the disulfido bridges and one or two quasi-reversible oxidation processes for Mo3S7ox32−or Mo3S7mnt32−, respectively. No oxidation waves have been observed for compound 1or for its thiocyanate derivative n-Bu4N2Mo3S7SCN64 within the acetonitrile solvent window. The optical limiting properties of the complexes 1–4have been measured by the Z-scan technique employing 40 ns pulses at 523 nm. Power limiting was observed for clusters 1, 2and 4, whereas the oxalate derivative 3was photochemically unstable under our experimental conditions.