( S )-Alanine ethyl ester tetra-cyanidoborate, (C 5 H 12 NO)[B(CN) 4 ].

The title mol-ecular salt, C 5 H 12 NO + ·C 4 BN 4 - or (C 5 H 12 NO)[B(CN) 4 ], was obtained as single crystals by slow evaporation of a solution of the compound in aceto-nitrile over several weeks. The asymmetric unit contains two ( S )-alanine ethyl ester cations and two tetra-cyanidoborate anions, which are linked by N-H⋯N hydrogen bonds. The compound exhibits a relatively low melting point of 110°C and shows a solid-solid phase transition near room temperature ( T s-s = 29°C) on the basis of DSC measurements.