Reactivity of the [MoS4Cu6Br8]4− anion toward polyarylphosphorus ligands: synthesis, characterization and nonlinear optical properties of [MoS4(Cudppf)2]·2DMF·CH3CN and [MoS4Cu2(Ph2PPy)4]

Abstract

[NH₄]₂[MoS₄] reacts with CuBr and [Bu₄N]Br in the solid state to afford an intermediate product with proposed constitution [Bu₄N]₄[MoS₄Cu₆Br₈] (1). Treatment of cluster (1) with an equal equivalent of dppf in CH₃CN–DMF solution resulted in the formation of a pentanuclear cluster [MoS₄(Cudppf)₂]·2DMF·CH₃CN (2). Cluster (2) crystallizes in the monoclinic space group P2₁/n with four formula units in a cell of dimensions a = 13.1267(8), b = 38.040(2), c = 15.2661(9) Å, and β = 97.6030(10)°. Refinement by full-matrix least-squares techniques gave final residuals R = 0.0567 and wR = 0.1679. The structure of (2) can be described as two (Cudppf)⁺ units linked through MoS₄²⁻ to form a pentanuclear folding-ruler array. Reaction of (1) with excess Ph₂PPy in CH₃CN solution resulted in the formation of a trinuclear cluster [MoS₄Cu₂(Ph₂PPy)₄] (3). Cluster (3) crystallizes in the tetragonal space group I4₁/a with cell constants a = 17.427(6), b = 17.427(6), c = 21.344(5) Å, and Z = 4. Final residuals R = 0.0337 and wR = 0.0616. The structure of (3) is built up from two Cu(Ph₂PPy)₂⁺ units bridged by a MoS₄²⁻ ligand to form a trinuclear symmetrical linear molecule. Clusters (2) and (3) exhibit strong optical absorption (effective α₂ = 1.6 × 10⁻⁹ m W⁻¹ (2) and 1.2 × 10⁻⁹ m W⁻¹ (3)) and optical self-defocusing effects (n₂ = −1.35 × 10⁻¹⁷ m² W⁻¹ (2) and −6.84 × 10⁻¹⁷ m² W⁻¹ (3)), their limiting thresholds were determined to be 0.35 J cm⁻² (2) and 0.65 J cm⁻² (3), which are about four and two times, respectively, better than that of C₆₀.