We report on the synthesis and structural characterization of unprecedented anionic parent compounds of mixed Group 13/15 elements. The reactions of the pnictogenylboranes H₂E-BH₂⋅NMe₃(1 a=P, 1 b=As) with phosphorus and arsenic centered nucleophiles of the type [EH₂]⁻(E=P, As) lead to the formation of compounds of the type [H₂E-BH₂-E′H₂]⁻(2: E=E′=P; 3: E=E′=As; 4: E=P, E′=As) containing anionic pnictogen–boron chain-like units. Furthermore, a longer 5-membered chain species [H₂As-BH₂-PH₂-BH₂-AsH₂]⁻(5) and a cyclic compound [NHC^dipp-H₂B-PH₂-BH₂-NHC^dipp]⁺[P₅B₅H₁₉]⁻(6) containing a n-butylcyclohexane-like anion were obtained. All the compounds have been characterized by X-ray structure analysis, multinuclear NMR spectroscopy, IR spectroscopy, and mass spectrometry. DFT calculations elucidate their high thermodynamic stability, the charge distribution, and give insight into the reaction pathway.