Synthesis of Two Heterobimetallic Cluster Isomers [(η5-C5Me5)2Mo2(μ3-S)3S(CuI)2] and [(η5-C5Me5)2Mo2(μ3-S)4(CuI)2] from trans-[(η5-C5Me5)2Mo2(μ-S)2S2] and Their trans-to-cis Isomerization, Structures, and Third-Order NLO Properties

Reaction of trans -[(η 5 -C 5 Me 5 ) 2 Mo 2 (μ-S) 2 S 2 ] ( 1 ) with 2 equiv of CuI in CH 2 Cl 2 at ambient temperature or in refluxing MeCN afforded two isomeric clusters, [(η 5 -C 5 Me 5 ) 2 Mo 2 (μ 3 -S) 3 S(CuI) 2 ] ( 2 ) and [(η 5 -C 5 Me 5 ) 2 Mo 2 (μ 3 -S) 4 (CuI) 2 ] ( 3 ). Compound 3 could also be prepared either by refluxing an acetonitrile solution of 2 or by heating 2 in the solid state at 120 °C. Compounds 2 and 3 were fully characterized by elemental analysis, IR, UV−vis, 1 H NMR, ESI-MS, and single-crystal X-ray crystallography. The molecular structure of 2 consists of an incomplete cubane-like core in which the trans structure of 1 was retained, while that of 3 contains a cubane-like core in which the trans structure of 1 was converted into the cis structure. The trans -to- cis isomerization from 2 to 3 either in solution or in the solid state was explored by means of 1 H NMR spectroscopy or X-ray powder diffraction. In addition, the third-order nonlinear optical (NLO) properties of 1 − 3 in CH 2 Cl 2 were investigated by using the Z -scan technique. The hyperpolarizability γ values for the two isomers (5.65 × 10 - 30 esu ( 2 ) and 1.18 × 10 - 29 esu ( 3 )) are larger than that of their cluster precursor 1 (3.07 × 10 - 30 esu).