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The absolute configuration of strictosidinic acid, (2 S,3 R,4 S)-3-ethenyl-2-(β- d-glucopyranosyloxy)-4-{[(1 S)-2,3,4,9-tetrahydro-1 H-pyrido[3,4- b]indol-1-yl]methyl}-3,4-dihydro-2 H-pyran-5-carboxylate, was determined from its sodium chloride trihydrate, poly[[diaqua((2 S,3 R,4 S)-3-ethenyl-2-(β- d-glucopyranosyloxy)-4-{[(1 S)-2,3,4,9-tetrahydro-1 H-pyrido[3,4- b]indol-2-ium-1-yl]methyl}-3,4-dihydro-2 H-pyran-5-carboxylate)sodium] chloride monohydrate], {[Na(C26H32N2O9)(H2O)2]Cl·H2O} n. The strictosidinic acid molecule participates in intermolecular hydrogen bonds of the O-H...O and O-H...Cl types. The solid-state conformation was observed as a zwitterion, based on a charged pyridine N atom and a carboxylate group, the latter mediating the packing through coordination with the sodium cation. [ABSTRACT FROM AUTHOR]

In the title compound, C6H10N2OS, the 2-sulfanylideneimidazolidin-4-one fragment is essentially planar (r.m.s. deviation = 0.0033 Å). In the crystal, one amino group is involved in N-H⋯O hydrogen bonding, which links pairs of mol-ecules into inversion dimers, while the other amino group generates weak N-H⋯S hydrogen bonds, which link these dimers into chains in [10-1]. The chains are further aggregated into layers parallel to the ac plane through weak C-H⋯O inter-actions.

The distribution of the d electrons over the corresponding orbitals in transition-metal complexes is a central concept in the theory of metal-ligand bonding. The description requires the assignment of an axis of quantization, which is unambiguous in symmetric environments but not clear-cut in the now commonly encountered case of a low-symmetry coordination environment. As the d-electron population can be derived from accurate diffraction data using the methods of charge-density analysis [HollaDay et al. (1983). Acta Cryst. A39, 377-387], the need for an appropriate procedure is relevant in this area of crystallography. Several criteria for the choice of coordinate system based on the resulting orbital populations are discussed. They are tested on a cobalt atom in a trigonal bipyramidal site and applied to transition-metal sites in Cu(II)-alanyl-valine, and an open zirconocene. The population of the d-orbital cross terms for the different coordinate-system orientations is used to judge the results. In the cases examined, the intuitively most reasonable coordinate system corresponds to the one with smaller value of the sum of the populations of the d-orbital cross terms.