Studies on two interesting microporous polymeric clusters {[Et4N]2[MS4Cu4(CN)4]}n (M = Mo or W) with three-dimensional open frameworks: synthesis, structural characterization, strong optical non-linearities and large optical limiting properties

Abstract

Reactions combining stoichiometric amounts of (Et4N)2MS4 (M = Mo or W) and CuCN (1∶4) in pyridine afforded interesting three-dimensional cluster polymers with open frameworks {[Et4N]2[MS4Cu4(CN)4]}n (M = Mo 1 or W 2). Crystal structure determination shows that the anionic MS4Cu4 units bridged by cyanide produce three-dimensional channels running down the crystallographic a axis. An alternative way to view this framework is in terms of the diamond structure, where C has alternately been replaced by a MS4Cu4 aggregate and C–C by two parallel cyanide bridging ligands. In these intersecting channels the shortest distances between Cu atoms along the b and c axes are 15.22 and 8.11 Å respectively. Non-linear optical properties of the two clusters were investigated first with an 8 ns pulsed laser at 532 nm. These two clusters exhibit large optical limiting performance with limiting threshold values of 0.28 for 1, 0.15 J cm−2 for 2 respectively. Both compounds show strong third-order NLO absorption effects (α2 1.5 × 10−91, 1.6 × 10−9 m W−12) and self-focusing performance (n2 1.84 × 10−161, 1.22 × 10−16 m2 W−12) in 3.64 × 10−51 and 2.93 × 10−5 mol dm−32 DMF solution separately. The corresponding effective NLO susceptibilities χ(3) are 4.58 × 10−91 and 5.12 × 10−9 esu 2 while the corresponding hyperpolarizabilities (γ(1) = 1.15 × 10−29 and γ(2) = 1.26 × 10−29 esu) are also reported.