Synthesis, characterization and optical non-linearity of two heterobimetallic copper clusters containing tetraselenometalates

Cluster [{MoCu₃Se₃Br}(PPh₃)₃Se]·THF·H₂O (1·3THF·H₂O) was prepared from reaction of [Et₄N]₂[MoSe]₄, Cu(PPh₃)₂NO₃ and Et₄N·Br in CH₂Cl₂ solution; also, 1 can be also obtained from the reaction of [MoSe₄Cu₄Py₆Br₂] and excess PPh₃ in a DMFCH₂Cl₂ mixture solvent. The ⁹⁵Mo NMR technique was used to monitor the above two reaction processes. X- ray crystallographic structure determination shows that it contains a strongly distorted cubane-like {MoCu₃Se₃Br} core. The coordination of the central Mo atom and each Cu atom are distorted from tetrahedral. Cluster [{WCu₃Se₃C1}(PPh₃)₃Se] (2) was synthesized by the reaction of [Et₄N]₂[WSe]₄ and Cu(PPh₃)₂Cl in the solid state for nonlinear optical (NLO) studies. Its structure was reported by Ibers (Inorg. Chem. 31 (1992) 4365). The NLO properties of clusters 1 and 2 were studied. Both NLO absorption and refraction were obtained, and their effective third-order non- linearities were detected with α₂ = 3.4 x 10^-10 and 5.9 x 10^-10 m/W and n₂ = - 1.5 X 10^-17 and - 1.3 x 10^-17 m²/W, respectively, for the same concentration CH₂C1₂ solution of 1 and 2. Influence of skeletal atoms to nonlinear absorption is also discussed in the paper. (C) 2000 Elsevier Science B.V.