Series clincher: The synthesis of salts of the [B(CO2H)4]− ion and the [B(CNCH3)4]3+ ion starting from [nBu4N][B(CN)4] are described. Thus, the series including [B(CN)4]−, [B(CO2H)4]−, and [B(CF3)4]− has now been completed. The figure shows the [B(CO2)2(CO2H)2]3− ion in [Co(NH3)6][B(CO2)2(CO2H)2]⋅2 H2O (O red, C black, B yellow, H white).