The molecular structures of gaseous tetrakis(dimethylamino)-diboron, B2(NMe2)4, and tetrakis(methoxy)diboron, B2(OMe)4, as determined by electron diffraction

Abstract

The structures of gaseous B₂(NMe₂)₄ and B₂(OMe)₄ have been determined by electron diffraction. The results indicate that the amine adopts the expected fully staggered conformation with D₂ symmetry whilst, surprisingly, the methoxy derivative has not a planar heavy-atom skeleton as thought previously, but a partially staggered conformation. Salient structural parameters (r_a) are (i) for B₂(NMe₂)₄, r(B–B) 176.2(1.1) and r(B–N) 140.8(3) pm; NBBN 90.0(1.1), NBN 124.0(5) and BBNC 19.7(1.1)°; and (ii) for B₂(OMe)₄, r(B–B) 172.0(6) and r(B–O) 136.9(3) pm; OBBO 49.5(1.2), OBO 119.9(4) and BBOC 12.1(2.7) and 21.9(1.9)°(clockwise and anticlockwise out of the BBO plane).