MYb(BH₄)₄ (M = K, Na) from laboratory X-ray powder data

The title compounds were prepared via a mechano­chemical reaction in the solid state. They crystallize in the NaSc(BH₄)₄ structure type composed of isolated [Yb(BH₄)₄]^- anions, with Yb coordinated tetra­hedrally by BH₄ groups, surrounded by M⁺ cations (M = Na, K) which form distorted trigonal prisms.