Role of Hydrogen-Bonding in the Formation of Polar Achiral and Nonpolar Chiral Vanadium Selenite Frameworks

A series of organically templated vanadium selenites
have been
prepared under mild hydrothermal conditions. Single crystals were
grown from mixtures of VOSO4, SeO2, and either
1,4-dimethylpiperazine, 2,5-dimethylpiperazine, or 2-methylpiperazine
in H2O. Each compound contains one-dimensional [VO­(SeO3)­(HSeO3)]nn‑ secondary
building units, which connect to form three-dimensional frameworks
in the presence of 2,5-dimethylpiperazine or 2-methylpiperazine. Differences
in composition and both intra-secondary building
unit and organic–inorganic hydrogen-bonding between compounds
dictate the dimensionality of the resulting inorganic structures.
[1,4-dimethylpiperazineH2]­[VO­(SeO3)­(HSeO3)]2 contains one-dimensional [VO­(SeO3)­(HSeO3)]nn‑ chains, while
[2,5-dimethylpiperazineH2]­[VO­(SeO3)­(HSeO3)]2·2H2O contains a three-dimensional
[VO­(SeO3)­(HSeO3)]nn‑ framework. The use of racemic 2-methylpiperazine also results in
a compound containing a three-dimensional [VO­(SeO3)­(HSeO3)]nn‑ framework, crystallizing
in the noncentrosymmetric polar, achiral space group Pca21 (no. 29), while analogous reactions containing either
(R)-2-methylpiperazine or (S)-2-methylpiperazine
result in noncentrosymmetric, nonpolar chiral frameworks that crystallize
in P21212 (no. 18). The formation
of these noncentrosymmetric framework materials is dictated by the
structure, symmetry, and hydrogen-bonding properties of the [2-methylpiperazineH2]2+ cations.