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

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 (ra) 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).