Why is the bond angle in dichlorine oxide larger than the expected tetrahedral angle?

Answer 1

Using VSEPR theory in its simple form you would expect the molecule to be bent and the lone pairs to repel the O-Cl bonds making the angle less than tetrahedral. Much as is the case in OH2 and OF2 Comparing the series of bond angles (N EN 3.04, O 3.44)

NH3 107.2 OH2 95.8

NF3 102.3 OF2 103.3

NCl3 106 OCl2 110.9

it is difficult to see a trend- other than the increase in angle as you go from the fluroide to the chloride. Prof. Gillespie (originator of VSEPR theory) in a paper (see link) talks about the effect of relative electronegativities and interligand distances. As you go from F to Cl the electronegativity decreases by 0.82. Following Prof Gillespies logic when the ligand is less electronegative than the central atom (as is the case in OCl2) the valence electrons are not so well localised and their effect on the geometry is weakened and interligand repulsions become more important.