Syntheses, crystal structures and third-order nonlinear optical properties of [PPh4]2[(WS4)M(μ-dppe)2M(WS4)]·2CH2Cl2 from the preformed polymeric clusters {[PPh4][WS4M]}n (M = Ag, Cu)

Reactions of {[PPh4][WS4M]}n (1: M = Ag; 2: M = Cu) with equimolar 1,2-bis(diphenylphosphino)ethane (dppe) in CH2Cl2 produced two tetranuclear anionic clusters [PPh4]2[(WS4)M(μ-dppe)2M(WS4)]·2CH2Cl2 (3: M = Ag; 4: M = Cu). Both clusters were characterized by elemental analysis, IR, UV–vis, 1H NMR and single-crystal X-ray analysis. The centrosymmetric structure of the cluster dianion of 3 or 4 consists of two [WS4M] cluster fragments linked by a pair of dppe ligands. The third-order nonlinear optical (NLO) properties of 3 and 4 in solution were investigated by femtosecond degenerate four-wave mixing (DFWM) technique with a 80-fs pulsed laser at 800 nm. Both compounds exhibited strong NLO performances with χ(3) = 3.30 × 10−14 esu (3) or 2.89 × 10−14 esu (4), and γ = 1.064 × 10−31 esu (3) or 1.059 × 10−31 esu (4).