Formation of dimeric and polymeric W/Cu/S clusters via degradation or expansion of the cluster core in [Et₄N]₄[WS ₄Cu₄I₆]

The reactions of a precursor cluster [Et₄N]₄[WS ₄Cu₄I₆] (1) with two equiv. of 1,1′-(1,4-butanediyl)bis(3,5-dimethyl-pyrazole) (bbd) or 1,3,5-tris(3,5-dimethyl-pyrazolyl-1-ylmethyl)-2,4,6-trimethylbenzene (tdtb) in MeCN/DMF afforded the dimeric clusters [WS₄Cu₃I(μ-bbd)] ₂ (2) and [{WS₄Cu₃(tdtb)}₂(μ-I) ₂]·2DMF (3·2DMF), respectively. Solvothermal reactions of 1 with two equiv. of bbd in MeCN/DMF at 90 °C for 24 h resulted in the formation of the dimeric cluster [Et₄ N]₆[{WS ₄Cu₅(μ-I)₂I₄}₂(μ- bbd)] (4) while those of 1 with two equiv. of 1,3,5-tris(imidazol-1-ylmethyl)-2, 4,6-trimethylbenzene (titb) in DMF at 120 °C afforded the polymeric cluster {[WS₄Cu₂(titb)]·0.5H₂O}_n (5). Compounds 2-5 were characterized by elemental analysis, IR, UV-vis, ¹H NMR and single-crystal X-ray crystallography. Compound 2 has a double nido-shaped structure in which two nido-shaped [WS₄Cu ₃] cores are connected by a pair of bbd ligands while 3 has a double butterfly-shaped structure in which two [WS₄Cu₃(tdtb)] fragments are linked by two bridging iodides. Compound 4 has a double-double half-open cubane-like structure in which a couple of double half-open cubane-like [WS₄Cu₅] cores are bridged by one bbd ligand. Compound 5 has a unique two-fold interpenetrated 3D (10²·12) _core(10²·12)_titb network in which each linear [WS₄Cu₂] core acts as a T-shaped 3-connecting node and each titb ligand works as a trigonal pyramidal 3-connecting node. The core structures of 2-5 are different from the saddle-shaped [WS₄Cu ₄] core of 1, which may be attributed to the degradation or expansion of the cluster core of 1 during the reactions. In addition, the third-order non-linear optical (NLO) properties of 1-4 in DMF were also investigated by using Z-scan techniques at 532 nm.