REACTIONS OF TRIANGULAR MO3S7X62- (X=CL, BR, NCS) COMPLEXES WITH KSCN AND KSECN, RESULTING IN STEREOSELECTIVE SUBSTITUTION OF SULFUR ATOM IN ASYMMETRICALLY COORDINATED MU-2-S2 LIGAND - X-RAY STRUCTURE OF (PPN)2MO3(MU-3-S)(MU-2-SSE)3CL6

The Mo3S7X6(2-) salts (X = Cl, Br, NCS) interact with KSeCN at room temperature in CH3CN to form KSCN and Mo3S4Se3(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 mu-2-S2 ligand. By treating (Et4N)2Mo3S4Se3(NCS)6 with conc. HCl(Et4N)2Mo3S4Se3Cl6 was prepared from which (PPN)2Mo3S4Se3Cl6 (IIIb) was obtained by the exchange of the cation. The structure of the latter was established by X-ray structural analysis. The crystals of IIIb are triclinic, space group P1, a = 13.650 (2), b = 18.159(3), c = 19.009(3) angstrom; alpha = 99.48(1), beta = 109.23(1), gamma = 109.32(1)-degrees, 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 Mo3 triangle. The S-Se distances are 2.156(5)-2.166(3) angstrom; Mo-Mo distances are 2.765(2)-2.787(2) angstrom. The equatorial sulfur of the mu-2-S2 group was found to undergo isotopic exchange with the thiocyanate sulfur. The interaction of (Et4N)2(Mo3S7Cl6)-S-34 with KSCN afforded, according to the vibrational spectroscopy data, (Et4N)2Mo3(mu-3-S-34)(mu-2-S-32-S-34)3(NCS)6.