Structures of two polymorphs of cis-TaBr4(PhPMe2)2

Abstract

The title compound, tetrabromobis- (dimethyl(phenyl)phosphine)tantalum(IV), (TaBr4- (CsH~ ~P):), Mr -- 77689, is polymorphic. Monoclinic (1), P2~/c, a=8.493 (8), b=30.369(9), c= 8.898 (5) A, /3 = 99.22 (2) °, V = 2265.5 A 3, Z = 4, Dx = 2.28 g cm -3, A(Mo Ka) = 0-71073 A, ~ = 119-2 cm- l, F(000) = 1444, room temperature, R = 0.0514 for 2065 observed reflections. Orthorhombic (2), P2~2,2~, a-- 14.38(1), b-- 19.17(1), c-- 828 (2) A, V = 2282 1 A 3, Z = 4, Dx = 228 g cm-3, A(Mo Ka) = 0.71073 A, ~ = 119.2 cm-1, F(000) -- 1444, room temperature, R=0.0455 for 1448 observed reflections. The structures of the two forms (1) and (2) consist of octahedrally coordinated Ta atoms with comparable values of interatomic dis- tances, and differ mainly in the angles between the average planes of the phenyl groups: 10.1 and 42.6 °, respectively. The crystals were obtained by reduction of TaBr5 with either one or two equivalents of sodium amalgam in toluene and in the presence of the phosphorus ligand. Experimental. All compounds are air sensitive; mani- pulations were performed under argon with anhydrous and deoxygenated solvents. Sodium amal- gam (95mg, 9-4ml) was added to TaBr5 (Alfa Inorganics) (825 mg) in 30 ml toluene and PhPMe2 (Aldrich) (0.75 ml) at room temperature. Stirring was maintained for 2 h, and after filtration and concen- tration, diffusion of pentane at room temperature offered 450 mg (35%) of brown-red needles of cis- TaBr4(PhPMe2)2, (1). A comparable reduction applied to TaBr5 (0.723 g) in 20ml toluene and PhPMe2 (0.60 ml) with one equivalent of sodium amalgam gave, after 3~ h reaction time, an olive- green filtrate. Concentration induced formation of crystals of different shapes, corresponding mainly to cis-TaBra(PhPMe2)2, (2), while (1) appears as a minor compound. Analysis: Calc. for C16H22BraP2Ta: C: 24.74 H: 2.83 P: 7-97 Br: 41.16. Found: C: 24.40 H: 2.82 P: 7.15 Br: 38.58. The monocrystals were introduced under argon into sealed Lindemann capillaries and mounted on an Enraf-Nonius automatic diffractometer. The basic information about data collection and struc- tural refinement is shown in Table 1. Cell param- eters from setting angles of 25 reflections (2 ° _< 0 __