Crystal structures of three sterically congested disilanes

In the three sterically congested silanes, C(24)H(38)Si(2) (1) (1,1,2,2-tetra­isopropyl-1,2-di­phenyl­disilane), C(24)H(34)Br4Si(2) (2) [1,1,2,2-tetra­kis­(2-bromo­propan-2-yl)-1,2-di­phenyl­disilane] and C(32)H(38)Si(2) (3) (1,2-di-tert-butyl-1,1,2,2-tetra­phenyl­disilane), the Si—Si bond length is shortest in (1) and longest in (2), with (3) having an inter­mediate value, which parallels the increasing steric congestion. A comparison of the two isopropyl derivatives, (1 and 2), shows a significant increase in the Si—C(ipso) distance with the introduction of bromine. Also, in the brominated compound 2, attractive inter­molecular Br⋯Br inter­actions exist with Br⋯Br separations ca 0.52 Å shorter than the sum of the van der Waals radii. In compound 2, one of the bromo­isopropyl groups is rotationally disordered in an 0.8812 (9):0.1188 (9) ratio. Compound 3 exhibits ‘whole mol­ecule’ disorder in a 0.9645 (7):0.0355 (7) ratio with the Si—Si bonds in the two components making an angle of ca 66°.