A new polymorph of tetra­phenyl­diboroxane

A new polymorph of tetra­phenyl­diboroxane [or oxybis(diphenyl­borane)], C₂₄H₂₀B₂O, (Ia), has been found. It is monoclinic, like the already known form, (Ib), and can be refined in the same space group, namely P2₁/c, or in the equivalent setting P2₁/n. The mol­ecular conformations of the two polymorphs differ in the rotations of two of the phenyl rings about the B-C bonds, leading to markedly different packing patterns and cell dimensions.