Density functional studies on trialkyl phosphorus selenide dibromide complexes R3PSeBr2 (R = H, Me, Et, N(CH3)2, N(C2H5)2, Ph, and C6H11)

R3PSeBr2 complexes where R is H, Me, Et, N(CH3)(2), N(C2H5)(2), Ph, or C6H11 and their parent compounds of the formula R3PSe have been studied in the gas phase at the density functional theory. Different stationary points on the molecular potential energy surface were located and characterized for each dihalide complex; two energy minima and many saddle points. The minima correspond to the molecular T-shaped (trigonal bipyramidal) and the molecular tetravalent angular geometry at the selenium centre where the dihalide in linear spoke structure. One of the saddle points corresponds to another isomer of the T-shaped structure where the BrSeBr species is almost eclipsed with two of the RP moieties. Solvent effects were modelled using self consistent reaction field Onsager model in the presence of cyclohexane and dichloromethane. Optimized geometries whether in the gas phase or in solution exhibit variation of the SeBr bond distances within the same T-shaped complex. The P-Se double bond character in the parent R3PSe compounds is no longer retained in the dibrominated ones, in addition, P-Se bond distances in the R3PSeBr2 complexes are found R-dependent. All energy calculations are found favouring the T-shaped adducts over the spoke ones. Onsager SCRF calculations reflected significant changes in the geometrical parameters in the R3PSeBr2 complexes in solvent with relatively high dielectric constant (dichloromethane) from that provided in the gas phase. (c) 2007 Elsevier B.V. All rights reserved.