Assembly of bicyclic or monocyclic clusters from [(η5-C5Me5)2Mo2(μ3-S)4(CuMeCN)2]2+ with tetraphosphine or N,P mixed ligands: syntheses, structures and enhanced third-order NLO performances

Abstract

Reactions of the preformed cluster [(η⁵-C₅Me₅)₂Mo₂(μ₃-S)₄Cu₂(MeCN)₂](ClO₄)₂ (1) with two tetraphosphine ligands, 1,4-N,N,N′,N′-tetra(diphenylphosphanylmethyl)benzene diamine (dpppda) and N,N,N′,N′-tetra(diphenylphosphanylmethyl)ethylene diamine (dppeda), produced two bicyclic clusters {[(η⁵-C₅Me₅)₂Mo₂(μ₃-S)₄Cu₂]₂(L)}(ClO₄)₄ (3: L = dpppda; 4: L = dppeda). Analogous reactions of 1 or [(η⁵-C₅Me₅)₂Mo₂(μ₃-S)₄Cu₂(MeCN)₂](PF₆)₂ (2) with two N,P mixed ligands, N,N-bi(diphenylphosphanylmethyl)-2-aminopyridine (bdppmapy) and N-diphenylphosphanylmethyl-4-aminopyridine (dppmapy), afforded two monocyclic clusters {[(η⁵-C₅Me₅)₂Mo₂(μ₃-S)₄Cu₂]₂(L)₂}X₄ (5: L = bdppmapy, X = ClO₄; 6: L = dppmapy, X = PF₆). Compounds 3–6 were fully characterized by elemental analysis, IR spectra, UV-vis spectra, ¹H and ³¹P{¹H} NMR spectra, ESI-MS and single-crystal X-ray crystallography. In the tetracations of 3–6, two cubane-like [Mo₂(μ₃-S)₄Cu₂] cores are linked either by one dpppda or dppeda bridge to form a bicyclic structure or by a pair of bdppmapy or dppmapy bridges to afford a monocyclic structure. The third-order nonlinear optical (NLO) properties of 1 and 3–6 in MeCN were also investigated by femtosecond degenerate four-wave mixing (DFWM) technique with a 50 fs pulse width at 800 nm. Compounds 3–6 exhibited enhanced third-order NLO performances relative to that of 1.