Two forms of sarcosine sarcosinium hydrogen L-tartrate

•There are four phases in the system sarcosine+L-tartaric acid+H2O.•The structure of two polymorphs of sarcosine sarcosinium hydrogen L-tartrate is determined.•This pair represents an instance of dimorphism with the same space group and Z.•Vibrational spectra of all four phases are shown and discussed. In the system sarcosine+L-tartaric acid+H2O we identified several new phases in addition to the previously known species sarcosinium hydrogen L-tartrate (I). Two of them (phases (II) and (III)) were obtained in the form of single crystals. Their crystal and molecular structures were determined. Both phases (II) and (III) have 2:1 composition and contain a zwitter-ionic sarcosine, a sarcosinium cation, and a hydrogen L-tartrate anion in the asymmetric unit and crystallize in the orthorhombic system (space group P212121). In the structure of (II), the sarcosinium cation forms a strong OH⋯O hydrogen bond (O⋯O distance equals 2.4553(15)Å) with the carboxylate group of the hydrogen L-tartrate anion, while the carboxyl group of the hydrogen L-tartrate anion forms an OH⋯O hydrogen bond (O⋯O distance equals 2.5065(14)Å) with the carboxylate group of sarcosine zwitter-ion. In the structure of (III) there are dimeric sarcosine sarcosinium cations with an O⋯O distance equal to 2.512(3)Å, while the hydrogen L-tartrate anions form hydrogen bonded usual infinite chains with O⋯O distances equal to 2.510(2)Å between carboxyl and carboxylate groups. Vibrational spectra (infrared and Raman) of (I), (II), (III) are shown and discussed on the basis of their structures. In addition, one more phase (IV) was identified by its infrared spectrum without structure determination.