Reactions of triangular Mo 3S 7X 62− (X=Cl, Br, NCS) complexes with KSCN and KSeCN, resulting in stereoselective substitution of sulfur atom in asymmetrically coordinated μ 2-S 2 ligand. X-ray structure of (PPN) 2Mo 3(μ 3-S)(μ 2-SSe) 3Cl 6

Abstract

The Mo 3S 7X 6 2− salts (X=Cl, Br, NCS) interact with KSeCN at room temperature in CH 3CN to form KSCN and Mo 3S 4Se 3(NCS) 6 2−. The stereochemistry of this reaction has been studied and it was shown that substitution only occurs at the equatorial sulfur atoms of the μ 2-S 2 ligand. By treating (Et 4N) 2Mo 3S 4Se 3(NCS) 6 with conc. HCl (Et 4N) 2Mo 3S 4Se 3Cl 6 was prepared from which (PPN) 2Mo 3S 4Se 3Cl 6 ( IIIb) was obtained by the exchange of the cation. The structure of the latter was established by X- ray structural analysis. The crystals of lIIb are triclinic, space group P1, a = 13.650 (2), b = 18.159(3), c = 19.009(3) Å; α = 99.48(1), β = 109.23(1), γ = 109.32(1)° Z = 2. With a total number of independent reflections of 7937, the structure has been solved to R = 0.054 ( R w = 0.077). The selenium atoms lie essentially in the plane of the isosceles Mo 3 triangle. The SSe distances are 2.156(5)–2.166(3) Å; MoMo distances are 2.765(2)–2.787(2) Å. The equatorial sulfur of the μ 2-S 2 group was found to undergo isotopic exchange with the thiocyanate sulfur. The interaction of (Et 4N) 2Mo 3 34S 7Cl 6 with KSCN afforded, according to the vibrational spectroscopy data, (Et 4N) 2Mo 3(μ 3- 34S)(μ 2- 32S 34S) 3(NCS) 6.