Hydrothermal Strategies Towards Polyoxofluoromolybdates(VI)

Abstract

The predictive hydrothermal synthesis of polyoxometalates (POMs) is an important challenge for their targeted production and for the design of new POM motifs and organic−inorganic POM materials. In this context, the systematic fluorination of POMs remains to be fully explored. Therefore, the structure-directing influence of cation pairs on the primary and secondary structure of polyoxofluoromolybdates(VI) is explored in the present study. In the first step, new types of mixed alkali difluorooctamolybdates ((M, M′)Mo8O26F2·nH2O; M, M′ = K−Cs) illustrate how the choice of the alkali cations controls the resulting structure type. This structure-directing potential of the cations is investigated in terms of electrostatic calculations. The concept of cation pairs as structural “spacers” and “scissors” is then applied to construct new secondary structures from the recently discovered [Mo6O18F6]6− and [Mo7O22F3]5− fluoromolybdate anions. The use of selected bicyclic organic cations (asn = 1-azoniaspiro[4,4]nonane; adu = 1-azonia-4,9-dioxaspiro[5,5]undecane) led to the new organic−inorganic fluoromolybdates asn 2Na4Mo6O18F6·6H2O, adu 3Na3Mo6O18F6·3H2O and adu 4NaMo7O22F3·4H2O. The steering effect of the organic cations in the formation of the layered organic−inorganic structures is compared for all three compounds with respect to their potential as building blocks for constructing POM-based materials.

A Unique Fluoride Nanocontainer: Porous Molecular Capsules Can Accommodate an Unusually High Number of “Rather Labile” Fluoride Anions

“…[18] We report herein the synthesis,X -ray crystal structure analysis,a nd NMR spectroscopic characterization of an unprecedented {Mo 132 }-type capsule (for stability of the general type see Supporting Information) containing approximately 60 fluoride ions.I ts hould be emphasized that this compound is quite different from other reported fluorooxomolybdates. [19] Thea cetate-type capsule 1a [16] is often used to obtain newc apsules through exchange of acetate ligands, [20] but complete replacement of the acetate ligands is sometimes difficult to achieve and above all the method does not apply to weakly coordinating ligands.F ortunately the carbonate-type capsule 2a [21] provides ac onvenient way to extend the scope of {Mo 132 }-type capsules because of the easy decomposition of the CO 3 2À ligands.Though the capsule 2a is stable in an aqueous solution in alimited range of pH values, CO 2 is released upon acidification which leads to ah ighly reactive capsule with alarge number of Mo V -type Lewis acid centers that are either coordinatively unsaturated or bound to easily exchangeable H 2 Ol igands and are therefore prone to bind alarge diversity of ligands even if these ligands are only weakly coordinating.For example,the addition of an aqueous solution of HF and (CH 3 ) 2 NH 2 Ft oas olution of 2 in water leads to the crystallization of compound 3 while the related compound 4 is obtained by pseudo-recrystallization of 3 in water (see Experimental Section). Compounds 3 and 4 were characterized by elemental analysis,s pectroscopic methods (IR, Raman and, to some extent, 19 FNMR) and X-ray crystallography.C ompound 4 was primarily investigated to gain information about the behavior of 3a in solution (easy release of the integrated water/fluoride species).…”

“…[17] In the context it is also worth noting that surfactant-encapsulated capsules can be integrated in supported liquid or lipid bilayer membranes. [19] Thea cetate-type capsule 1a [16] is often used to obtain newc apsules through exchange of acetate ligands, [20] but complete replacement of the acetate ligands is sometimes difficult to achieve and above all the method does not apply to weakly coordinating ligands.F ortunately the carbonate-type capsule 2a [21] provides ac onvenient way to extend the scope of {Mo 132 }-type capsules because of the easy decomposition of the CO 3 2À ligands.Though the capsule 2a is stable in an aqueous solution in alimited range of pH values, CO 2 is released upon acidification which leads to ah ighly reactive capsule with alarge number of Mo V -type Lewis acid centers that are either coordinatively unsaturated or bound to easily exchangeable H 2 Ol igands and are therefore prone to bind alarge diversity of ligands even if these ligands are only weakly coordinating.For example,the addition of an aqueous solution of HF and (CH 3 ) 2 NH 2 Ft oas olution of 2 in water leads to the crystallization of compound 3 while the related compound 4 is obtained by pseudo-recrystallization of 3 in water (see Experimental Section). [19] Thea cetate-type capsule 1a [16] is often used to obtain newc apsules through exchange of acetate ligands, [20] but complete replacement of the acetate ligands is sometimes difficult to achieve and above all the method does not apply to weakly coordinating ligands.F ortunately the carbonate-type capsule 2a [21] provides ac onvenient way to extend the scope of {Mo 132 }-type capsules because of the easy decomposition of the CO 3 2À ligands.Though the capsule 2a is stable in an aqueous solution in alimited range of pH values, CO 2 is released upon acidification which leads to ah ighly reactive capsule with alarge number of Mo V -type Lewis acid centers that are either coordinatively unsaturated or bound to easily exchangeable H 2 Ol igands and are therefore prone to bind alarge diversity of ligands even if these ligands are only weakly coordinating.For example,the addition of an aqueous solution of HF and (CH 3 ) 2 NH 2 Ft oas olution of 2 in water leads to the crystallization of compound 3 while the related compound 4 is obtained by pseudo-recrystallization of 3 in water (see Experimental Section).…”

“…[18] We report herein the synthesis,X -ray crystal structure analysis,a nd NMR spectroscopic characterization of an unprecedented {Mo 132 }-type capsule (for stability of the general type see Supporting Information) containing approximately 60 fluoride ions.I ts hould be emphasized that this compound is quite different from other reported fluorooxomolybdates. Compounds 3 and 4 were characterized by elemental analysis,s pectroscopic methods (IR, Raman and, to some extent, 19 FNMR) and X-ray crystallography.C ompound 4 was primarily investigated to gain information about the behavior of 3a in solution (easy release of the integrated water/fluoride species). Compounds 3 and 4 were characterized by elemental analysis,s pectroscopic methods (IR, Raman and, to some extent, 19 FNMR) and X-ray crystallography.C ompound 4 was primarily investigated to gain information about the behavior of 3a in solution (easy release of the integrated water/fluoride species).…”

A binuclear molybdenum oxyfluoride: μ-oxido-bis[(2,2′-bipyridyl)fluoridodioxidomolybdenum(VI)]

“…For oxidofluoridomolybdates and -vanadates, see: Adil et al (2010); Burkholder & Zubieta (2004); Jones et al (2010); Michailovski et al (2006Michailovski et al ( , 2009 Table 1 Hydrogen-bond geometry (Å , ). (5) 3.199 (6) 120 (4) Symmetry codes: (i) x À 1; y; z; (ii) Àx; Ày þ 1; Àz þ 1; (iii) Àx; y þ 1 2 ; Àz þ 1 2 ; (iv) Àx þ 1; y þ 1 2 ; Àz þ 1 2 ; (v) Àx þ 1; Ày þ 1; Àz.…”

“…One area of oxide chemistry that has witnessed considerable activity is that of zeolitic materials, compositions forming open-framework structures consisting of metal oxide components and organic moieties acting as charge compensating cations, structure-directing agents or ligands. While the majority of these materials are simple oxides or oxyanion based, the introduction of fluoride to substitute for some oxo-groups provides a novel class of oxyfluorometalates (Adil et al, 2010;Jones, et al, 2010;Michailovski, et al, 2006 and2009;Burkholder and Zubieta, 2004).…”