Evolution of the Structural Chemistry of Vanadium Organodiphosphonate Networks and Frameworks:  Structural Consequences of Fluoride Incorporation in the Development of Stable Phases with Void Channels

Abstract

Hydrothermal reactions of solutions containing a vanadate source, an organodiphosphonate, an organonitrogen component, and HF (V/P/O/F) yield a series of oxyfluorovanadium-diphosphonates with charge-compensation provided by organoammonium cations or hydronium cations. While V/P/O/F networks provide the recurrent structural motif, the linkage between the layers and the details of the polyhedral connectivities within the layers are quite distinct for the five structures of this study. [H2pip][V4F4O2(H2O)2{O3P(CH2)3PO3}2] (1) (pip = piperazine) is a conventional three-dimensional (3D) "pillared" layer structure, whose V/P/O/F networks are buttressed by the propylene chains of the diphosphonate ligands. In contrast, [H2en][V2O2F2(H2O)2{O3P(CH2)4PO3}] (2) and [H2en]2[V6F12(H2O)2{O3P(CH2)5PO3}2 {HO3P(CH2)5PO3H}] (3) are two-dimensional (2D) slablike structures constructed of pairs of V/P/O/F networks sandwiching the pillaring organic tethers of the diphosphonate ligands. Despite the common overall topology, the layer substructures are quite different: isolated {VO5F} octahedra in 2 and chains of corner-sharing {VO(3)F(3)} octahedra in 3. The 3D structure of [H2en]2[V7O6F4(H2O)2{O3P(CH2)2PO3}4].7H2O (4.7H2O) exhibits a layer substructure that contains the ethylene bridges of the diphosphonate ligands and are linked through corner-sharing octahedral {VO6} sites. The connectivity requirements provide large channels that enclose readily removed water of crystallization. The structure of [H3O][V3F2(H2O)2{O3P(CH2)2PO3}2].3.5H2O (5.3.5H2O) is also 3D. Because of the similiarity with 4.7H2O, it exhibits V/P/O/F layers that include the organic tethers of the diphosphonates and are linked through corner-sharing {VO6} octahedra. In contrast to the network substructure of 4.7H2O, which contains binuclear and trinuclear vanadium clusters, the layers of 5.3.5 H2O are constructed from chains of corner-sharing {VO4F2} octahedra. Thermal studies of the open framework materials 4 and 5 reveal that incorporation of fluoride into the inorganic substructures provides robust scaffoldings that retain their crystallinity to 450 degrees C and above. In the case of 4, dehydration does not change the powder X-ray diffraction pattern of the material, which remains substantially unchanged to 450 degrees C. In the case of 5, there are two dehydration steps, that is, the higher temperature process associated with loss of coordinated water. This second dehydration results in structural changes as monitored by powder X-ray diffraction, but this new phase is retained to ca. 450 degrees C. The materials of this study exhibit a range of reduced oxidation states: 1 is mixed valence V(IV)/V(III) while 2 and 4.7H(2)O are exclusively V(IV) and 3 and 5.3.5H2O are exclusively V(III). These oxidation states are reflected in the magnetic properties of the materials. The paramagnetism of 1 arises from the presence of V(III) and V(IV) sites and conforms to the Curie-Weiss law with C = 2.38 em K/(Oe mol) and = -66 K with mu(eff) (300 K) = 4.33 mu(B). Compounds 3-5 ...

Solid state coordination chemistry of the oxofluorovanadium–diphosphonate system in the presence of Cu(II)–tetrapyridylpyrazine complex cations

“…The contrasting dimensionalities of 1 and 2 are consistent with bonding patterns previously established for diphosphonate ligands [49,65]. Thus, the methylenediphosphonate ligand does not possess the spatial extension to span adjacent clusters so as to generate chain motifs of the type {-cluster-O 3 PCH 2 PO 3 -} n , but rather adopts chelating modes with a single metal site or bridging geometries to metal sites of a single cluster.…”

Solid state coordination chemistry of the oxovanadium-diphosphonate system: Structural consequences of aryl tethers on materials of the type cation/VxOy/diphos, where cation=organoammonium and diphos=1,4-phenyldiphosphonic acid

“…The reaction mixture consisted of vanadium(V) oxide, the appropriate organoamine, 1,4-diphosphonic acid, and HF in water with reaction temperatures in the range 100-200°C and reaction times of 3-7 days. While HF is generally added as a mineralizer to induce solubility and crystal growth rather than as a constituent of the product, oxyfluorinated products are not unusual for hybrid oxides of vanadium and molybdenum [41,53,54]. In most cases, fluoride incorporation into the product requires relatively high HF/V ratios (3:1 or greater).…”

“…While the buttressed layer motif is a recurrent theme of the structural chemistry of the oxovanadium-diphosphonate phases, considerable structural variation results from factors such as tether length, replacement of oxo-groups by fluoride and introduction of aryl tethering groups [39][40][41][42][43]. For example, within the family of materials of the general type [V x O y {O 3 P(CH 2 ) n PO 3 } z ] with a, x-alkyldiphosphonate ligands, when n = 2-5, the prototypical buttressed layer structure is observed, while two-dimensional structures occur for n = 6-8 and structures characterized by V-P-O double layers for n = 9 and 10 (Scheme 1).…”

Syntheses, structures, thermal stabilities and luminescence of two new 3D zinc phosphonates

“…Homochiral zinc and lanthanide phosphonates display 1D triple-strand helical chains and selective adsorption capacities for N 2 , H 2 O and CH 3 OH molecules [21,22]. Furthermore, an important subject is to introduce organic amines as structure-directing agents to achieve various phosphonates, like mixed-valence vanadium phosphonoacetates with 16MR channels, and zinc phosphonates with tunable emission [23][24][25][26][27][28]. In this regard, Zheng et al have successfully exploited 1,4-butanediamine as a structure-directing agent to tune the structures and properties of metal 1-hydroxyethylidenediphosphonates [29][30][31][32][33][34][35].…”