Two interesting heterobimetallic compounds [MOS3Cu3(4-pic)6]·Br (M=Mo, W) with cationic cluster: synthesis, structural characterization, non-linear response and large optical limiting properties

Two heterobimetallic cluster compounds [MOS3Cu3(4-pic)6]·Br (M=Mo, W) with cationic cluster skeleton and halide anion Br− synthesized by the reaction of (NH4)2MOS3, CuBr and 4-picoline (4-pic) are presented. Their structures have been crystallographically determined and such nest-shaped cationic clusters, obtained for the first time, are interesting in comparison with the analogical nest-shaped clusters with a neutral skeleton or anionic skeleton. The non-linear optical (NLO) properties of these two clusters are investigated with an 8 ns pulsed laser at 532 nm. These two clusters exhibit large optical limiting abilities with limiting thresholds Fth=0.18 J cm−2 (1) and Fth=0.15 J cm−2 (2), respectively. Both compounds show strong third-order NLO absorption effects (α2-value of 1.6×10−10 m W−1 (1), 2.8×10−10 m W−1 (2)) and self-focusing performance (n2-value of 4.56×10−11 esu (1), 4.62×10−11 esu (2)) in 3.86×10−4 mol dm−3 (1) and 8.89×10−4 mol dm−3 (2) DMF solution separately. The corresponding effective NLO susceptibilities χ(3) are 5.4×10−12 esu (1) and 5.5×10−12 esu (2) while the corresponding hyperpolarizabilities (γ(1)=2.51×10−31 esu and γ(2)=1.03×10−31 esu) are also reported.