The 70·6 MHz 11B NMR spectrum of B10H13− consists of four doublets of relative intensities 2:1:5:2 which are assigned to B(6, 9); B(1 or 3): B(5, 7, 8, 10 and 1 or 3); and B(2,4) respectively. This data is consistent with a 3630 model for the solution structure.