OCTAHEDRAL TANTALUM AND NIOBIUM CLUSTER COMPLEXES WITH CHLORO AND TRIALKYLPHOSPHINE LIGANDS - ISOLATION AND STRUCTURE DETERMINATION OF THE TRANS AND CIS ISOMERS

Both trans and cis isomers of the octahedral tantalum clusters [(Ta6Cl12)Cl2(PR3)4] (R = C2H5, C3H7, and C4H9) have been isolated by the column chromatography. Oxidation of these neutral isomers by NOBF4 has yielded the trans and cis isomers of the mono- and dicationic complexes. No isomerization reaction was observed. Though the electronic spectra of the neutral isomers are almost identical, the trans and the cis isomers of [Ta6Cl14{P(C2H5)3}4]n+ (n = 1, 2) show different absorption bands around 13 × 103 cm−1, which indicates the splitting of a metal cluster orbital (t1u or t2g) due to the lowering of the symmetry from Oh. For the niobium derivatives, only the trans isomers have been obtained. The structures of the following complexes have been determined by the X-ray diffraction method. Crystallographic data: trans-[Ta6Cl14{P(C2H5)3)4]•CHCl3, Pbca, a = 21.974 (6) Å, b = 22.603 (7) Å, c = 12.099 (2) Å, Z = 4; trans-[Ta6Cl14{P(C2H5)3}4] [BF4]•CHCl3, P21/a, a = 19.874 (3) Å, b = 15.595 (2) Å, c = 10.019 (2) Å, β = 93.47 (2)°, Z = 2; cis-[Ta6Cl14{P(C2H5)3}4][BF4]•3CH2Cl2, P21/m, a = 16.888 (4) Å, b = 16.141 (5) Å, c = 12.045 (2) Å, β = 93.88 (2)°, Z = 2; trans-[Nb6Cll4(P(C4H9)3)4], [formula omitted], a = 15.923 (2) Å, b = 20.881 (3) Å, c = 12.311 (2) Å, α = 92.53 (1)°, β = 106.47 (1)°, γ = 90.22 (1)°, Z = 2. The bond distances between the metals in the cluster depend not only on the oxidation state of the cluster but also on the kind of the terminal ligands on each metal. © 1990, American Chemical Society. All rights reserved.