Directed Synthesis of Noncentrosymmetric Molybdates Using Composition Space Analysis

A systematic investigation of the factors governing the reaction product composition, hydrogen bonding, and symmetry
was conducted in the MoO3/3-aminoquinuclidine/H2O system. Composition space analysis was performed through
36 individual reactions under mild hydrothermal conditions using racemic 3-aminoquinuclidine. Single crystals of
three new compounds, [C7H16N2][Mo3O10]·H2O, [C7H16N2]2[Mo8O26]·H2O, and [C7H16N2]2[Mo8O26]·4H2O, were grown.
The relative phase stabilities for these products are dependent upon the reactant mole fractions in the initial reaction
gel. This phase stability information was used to direct the synthesis of two new noncentrosymmetric compounds,
using either (S)−(−)-3-aminoquinuclidine dihydrochloride or (R)-(+)-3-aminoquinuclidine dihydrochloride. [(R)-C7H16N2]2[Mo8O26] and [(S)-C7H16N2]2[Mo8O26] both crystallize in the noncentrosymmetric space group P21 (No. 4), which
has the polar crystal class 2 (C2). The second-harmonic generation activities were measured on sieved powders.
The structure-directing properties of the molybdate components in each compound were determined using bond
valence sums. The structures of all five compounds were determined using single-crystal X-ray diffraction.