RESUMEN
Two new noncentrosymmetric polar gallium fluorophosphates have been synthesized under mild hydrothermal conditions through the use of enantiomorphically pure sources of either R-2-methylpiperazine or S-2-methylpiperazine. A centrosymmetric analogue was also prepared using a racemic source of the amine. Novel [Ga(3)F(PO(4))(4)](n)(4n-) layers, constructed from [Ga(3)O(3)F(PO(4))(4)] building units, are observed in all three compounds. The use of racemic 2-methylpiperazine results in crystallographic disorder of the amines and creation of inversion centers, while using a single enantiomer destroys the inversion symmetry and orders the amines. Second harmonic generation measurements were performed on [(R)-C(5)H(14)N(2)](2)[Ga(3)F(PO(4))(4)] x 5.5 H(2)O and [(S)-C(5)H(14)N(2)](2)[Ga(3)F(PO(4))(4)] x 4.75 H(2)O, both of which display type 1 phase-matching capabilities and exhibit activities of approximately 50 x alpha-SiO(2). The structures of these compounds were determined using single crystal X-ray diffraction, infrared spectroscopy, and thermal analyses. [C(5)H(14)N(2)](2)[Ga(3)F(PO(4))(4)] x 5.25 H(2)O, a = 13.0863(5) A, c = 9.9023(4) A, trigonal, P-3 (No. 147), Z = 2; [(R)-C(5)H(14)N(2)](2)[Ga(3)F(PO(4))(4)] x 5.5 H(2)O, a = 13.0887(2) A, c = 29.9439(4) A, trigonal, P3(1) (No. 144), Z = 6; [(S)-C(5)H(14)N(2)](2)[Ga(3)F(PO(4))(4)] x 4.75 H(2)O, a = 13.0871(2) A, c = 29.8350(6) A, trigonal, P3(2) (No. 145), Z = 6.
RESUMEN
The use of second-order Jahn-Teller active Mo (VI) centers and chiral organic amines is discussed as an approach to crystallographic noncentrosymmetry. Several series of reactions, conducted under mild hydrothermal conditions, were designed to probe important reaction variables. Correlations between reagent and solvent concentrations and the molybdate structure were investigated using composition space analysis, which allows for the isolation of specific reaction variables. The effects of amine structure variation were probed using multiple series of related amines, which consisted of either linear diamines or ethylenediamine derivatives. The addition of fluoride results in the loss of amine-based structural variations. Chiral organic amines were used to demonstrate the viability of using such components to control the three-dimensional symmetry in new materials. The synthesis, structure, and characterization of eight new organically templated polyoxomolybdates and polyoxofluoromolybdates are reported.
Asunto(s)
Molibdeno/química , Aminas/química , Cristalografía por Rayos X , Indicadores y Reactivos/química , EstereoisomerismoRESUMEN
Single crystals of a new beta-octamolybdate salt containing protonated 1,4-diazabicyclo[2.2.2]octane cations were prepared under mild hydrothermal conditions. This compound, [C6H13N2]2[C6H14N2][Mo8O26], was then used as a starting material in the synthesis of [C6H13N2]6[Mo16O53F2].4H2O, which contains previously unreported [Mo16O53F2]12- anions. The structure-directing properties of gamma-[Mo8O26]4-, a likely intermediate in this pH-dependent transformation, are responsible for the site selection of the fluoride incorporation. [Mo16O53F2]12-, the largest reported polyoxofluoromolybdate cluster, expands upon the limited number of such anions in the literature. The structures of both compounds were determined using single-crystal X-ray diffraction.