Packing and polytypism in 1,10-phenanthrolin-1-ium (2-carboxyethyl)(2- carboxylatoethyl)dichloro-stannate(IV)

The 1:1 adduct of [SnCl₂(C₂H₄COOCH ₃] and 1,10-phenanthroline, (C₁₂H₈N ₂), which was set aside for 25 years, when recrystallized from ethanol was found to be the salt [C₁₂H₉N₂] ⁺·[SnCl₂(C₂H₄COO)(C ₂H₄COOH)]^-. The Sn^IV atom in the anion has pseudo-octahedral coordination with two cis Cl atoms, two C atoms and two O atoms trans to the Cl atoms. The possibility of alternative stacking of layers perpendicular to c* offers an explanation for observed twinning and polytypism. An ordered, untwinned, Z = 2 crystal structure was determined. Pairs of adjacent anions are linked together by strong intermolecular O-H⋯O^- hydrogen bonds, and the cation contains a strong intramolecular N-H⋯N hydrogen bond between its two N atoms. The protonated ring of the cation exhibits increased Lewis acidity and is linked into a network with the anions using a strong N-H⋯O and weak C-H⋯O and C-H⋯Cl interactions. The remaining rings of the cation form weaker C-H⋯O and C-H⋯Cl interactions. The cations stack in columns along a with an interplanar spacing of 3.24 Å for separations between cations inversion-related about (1, 1/2, 1/2) and 3.34 Å for separations between cations inversion-related about (1/2, 1/2, 1/2).