Synthesis and Theoretical Studies of the Stability of Tetrahalide Tungsten Molecular Complexes <i>trans-</i> [WX ₄ (OPPh ₃ ) ₂ ] (X = Cl, Br, or I)

The work is devoted to theoretical and experimental studies of the synthesis and stability of tungsten tetrahalide complexes <i>trans</i>-[WX₄(OPPh₃)₂] (X = Cl, Br, or I). New molecular complexes of tungsten(IV) <i>trans</i>-[WCl₄(OPPh₃)₂] (<b>I</b>) and <i>trans</i>-[WBr₄(OPPh₃)₂] (<b>II</b>) were obtained in the form of polycrystalline powders starting from different tungsten sources: oxotetrahalides, hexahalides, or trioxide, in the presence of triphenylphosphine and triphenylphosphine oxide. The X-ray crystal structures were determined for <b>I</b> and <b>II</b> (<b>I:</b> <i>P</i>-1, <i>a</i> = 9.3841(10) Å, <i>b</i> = 9.6332(10) Å, <i>c</i> = 10.4243(13) Å, α = 101.585(4)°, β = 108.097(4)°, γ = 93.365(4)°, <i>Z</i> = 1, <i>V</i> = 870.03(17) ų; <b>II:</b> <i>P-</i> 1, <i>a</i> = 9.5326(5) Å, <i>b</i> = 9.5946(5) Å, <i>c</i> = 10.7150(7) Å, α = 102.387(2)°, β = 107.898(2)°, γ = 94.308(2)°, <i>Z</i> = 1, <i>V</i> = 900.32(9) ų). Magnetic susceptibility measurements revealed Van Vleck-type paramagnetism for the compounds. In order to estimate the enthalpy of the studied reactions and predict the existence of <i>trans</i>-[WI₄(OPPh₃)₂], DFT calculations were performed. The article discusses the synthesis of new complex compounds <b>I</b> and <b>II</b>, their crystal structures and magnetic properties, and the results of DFT calculations for the reactions involved in the formation of <i>trans</i>-[WX₄(OPPh₃)₂] (X = Cl, Br, or I).