Darstellung,Kristallstrukturen, Schwingungsspektren und Normalkoordinatenanalyse von [(Mo6Br)Y]2−; Ya  CN,NCS

Preparation, Crystal Structures, Vibrational Spectra, and Normal Coordinate Analysis of [(Mo₆Br )Y ]^2?; Y^a ? CN, NCS By treatment of [(Mo₆Br)Br^a₆]^2? with AgNO₃ in acetone and addition of KCN or KNCS the hexacyano and hexaisothiocyanato derivates [(Mo₆Br)Y]^2?, Y^a ? CN, NCS are formed. X-ray structure determinations of (Ph₄P)₂ [(Mo₆Br)(CN)^a₆]·4H₂ O ( 1 ) (triclinic, spacegroup P1, a = 11.63(3), b = 11.85(1), c = 14.23(5) Å, α = 71.8(1)°, β = 67.6(3)°, γ = 62.8(1)°, Z= 1) and (n-Bu₄N)₂[(Mo₆Br ⁱ₈)(NCS)^a₆] · 2Et₂O ( 2 ) (monoclinic, spacegroup P2₁/n, a = 11.483(3), b = 16.348(5), c = 20.059(6) Å, β= 95.44(3)°, Z = 2) have been performed. The via C coordinated cyano ligands of ( 1 ) reveal facial groups with (MoCN) angles of 168.0–171,5° and 174.1°–175.7°. In ( 2 ) the via N coordinated isothiocyanato groups at the apical positions show MoNC-angles of 164.4°, the equatorial angles are 172.7–173.5°. Using the molecular parameters of the X-ray determinations the 10 K IR and Raman spectra of the (n-Bu₄N) cluster salts are assigned by normal coordinate analyses based on a modified valence force field. The valence force constants are f_d(MoMo) = 1.41 (CN^a), 1.43 (NCS^a), f_d (MoBrⁱ) = 0.97 (CN^a), 0.96 (NCS^a), f_d(MoC) = 1.62, f_d(Mo-N) = 2.09 mdyne/Å.