Synthesis, Crystal Structure, and Thermal Behavior of Organically Templated Three-Dimensional Tunnel Structures Based on α-Keggin Phosphododecamolybdate and Diazines

Abstract

Three salts of diazonium cation (C 4 H 5 N 2 + ) encapsulated R-Keggin phosphododecamolybdate, (pyridazinium) 3 [PMo 12 O 40 ]‚ 1 / 2 H 2 O (1), (pyrimidinium) 3 [PMo 12 O 40 ]‚3H 2 O (2), and (pyrazinium) 3 [PMo 12 O 40 ]‚3H 2 O (3) have been synthesized at room temperature and atmospheric pressure in an organic-aqueous medium. Compounds 1-3 crystallize in the trigonal space group R3 h. Crystal data for compound 1 is as follows: a ) 17.704(6) Å, c ) 22.918(3) Å, V ) 6221(3) Å 3 , Z ) 6, R ) 0.028 for 3708 observed reflections with I > 3σ(I); for compound 2, a ) 19.022(1) Å, c ) 21.524(1) Å, V ) 6745(1) Å 3 , Z ) 6, and R ) 0.043 for 2143 observed reflections with I > 2σ(I); for compound 3, a ) 17.820(2) Å, c ) 24.369(2) Å, V ) 6701(1) Å 3 , Z ) 6, and R ) 0.047 for 3699 observed reflections with I > 3σ(I). These compounds contain the Keggin clusters arranged in a three-dimensional tunnel structure where the organic templates are sandwiched by two polyanions. Although the three salts are isostructural, the arrangement of organic cations and water molecules relative to the polyanion framework shows some significant differences that have been analyzed by means of ab initio calculations. Differences in the thermal behavior of the three compounds have also been explained on the basis of the different crystal arrangements.

Computational Study of the Vibrational Spectra of α‐ and β‐Keggin Polyoxometalates

“…The atom numbering is defined in Figure 1 and 2 with primed atoms located on the rotated [M 3 O 13 ] unit of the b isomer. The averaged experimental [25,26] from the present STO study, together with calculated intensities. A full list of calculated frequencies and a description of the nature of the vibrations is available in the Supporting Information.…”

“…Structures of the a-and b-isomers of [PMo 12 O 40 ] 3À : Table 1 lists optimized MÀO and XÀO bond lengths together with the available experimentally determined distances [25,26] for the a-and b-isomers of [PMo 12 O 40 ]…”

Conductive Inorganic–Organic Hybrid Layered Crystals Composed of Keggin‐Type Polyoxotungstates and a Heterocyclic Surfactant

“…The alkyl chains of the bent C 12 pda cations round the surface of PW 12 through the C–H ··· O hydrogen bonds, with the C ··· O distances ranging from 2.96 to 3.85 Å. The pyridazine rings of C 12 pda have no interaction each other, such as π–π stacking or C–H ··· π interaction, and interact directly with the PW 12 anions, which is similar to other POM crystals containing pyridazine derivatives , …”

“…Each SiW 12 anion is isolated by the hydrophilic heads of C 12 pda penetrating into the SiW 12 inorganic monolayers, which is similar to other POM hybrid crystals hybridized with heterocyclic surfactants . The pyridazine rings of C 12 pda interact directly with the SiW 12 anions without π–π stacking or C–H ··· π interaction, as observed in 1 , . The C atoms of the pyridazine ring are electron‐deficient (“π‐deficient”), due to the presence of electronegative N atoms.…”

A novel 1D chain compound constructed from copper-complex fragments-substituted dilacunary β-octamolybdate units and saturated β-octamolybdate clusters

“…The second huge mass loss can be assigned to the phen ligands (exptl 21.11%, calcd 22.51%). The relatively high temperature of dehydration for 1 reflects the presence of all water molecules as structural water, rather than as waters of crystallization [28].…”