The preparation of [NMC][B5O6(OH)4] {NMC = 2-MeC3N2H4 (3),1-MeC3N2H4 (4), 4-MeC3N2H4 (5), 1,2-Me2C3N2H3 (6), 1,2,3-Me3C3N2H2 (7), 1-EtC3N2H4 (8), 2-EtC3N2H4 (9), 2-Et-4-MeC3N2H3 (10) 1-Et-3-MeC3N2H3 (11) and 2-iPrC3N2H4 (12)} salts are reported. Compounds were characterised by spectroscopy (NMR and IR) and by single crystal XRD (6, 7, 9, 10, 12) studies. All structures show extensive H-bonded networks and 7 displays the first example of reciprocal paired αααα anion–anion interactions. These are facilitated by the pentaborate boroxole rings being significantly distorted (boat) from the near-planar arrangements more commonly observed. The related imidazolinium salt, [2-MeC3N2H6][B5O6(OH)4] (13), has also been characterised by XRD studies. Compound 13 is isostructural with 3. Thermal properties (TGA/DSC) indicate decomposition to B2O3via [NMC][(B5O8)n] intermediates.