Controlling Nucleation and Crystal Growth of a Distinct Polyoxovanadate Cluster: An In Situ Energy Dispersive X‐ray Diffraction Study under Solvothermal Conditions

Abstract

The formation of the antimonato polyoxovanadates [V(14)Sb(8)(C(6)H(15)N(3))(4)O(42)(H(2)O)]·4H(2)O (1), (C(6)H(17)N(3))(2)[V(15)Sb(6)(C(6)H(15)N(3))(2)O(42)(H(2)O)]·2.5H(2)O (2), {C(6)H(15)N(3)}(4)[V(16)Sb(4)O(42)]2H(2)O (3) (C(6)H(15)N(3)=1-(2-aminoethyl)piperazine, AEP) has been studied under solvothermal conditions by using in situ energy dispersive X-ray diffraction (EDRXD). The syntheses were performed with an identical ratio for Sb(2)O(3) and NH(4)VO(3). If the reactions slurries are not stirred during the solvothermal reaction and by applying 70-75% amine concentration, the products contain all three compounds, whereas 3 is observed at 80%. Under stirring conditions, variation of the concentration of AEP led to crystallization of the three different compounds at distinct concentrations, that is, 1 is formed at 75%, 1 and 2 between 75 and 80% and 3 at 80%. At an amine concentration of 77.5%, first reflections of 2 occurred and at later stages, compound 1 started to crystallize. The sample with the lowest number of V(IV) species was formed at the lowest amine concentration, whereas crystallization of 3 required the highest concentration. The formation of the compounds occurred without crystalline intermediates and/or precursors. With increasing reaction temperature, the incubation time was significantly reduced.

Catalysis of “outer-phase” oxygen atom exchange reactions by encapsulated “inner-phase” water in {V15Sb6}-type polyoxovanadates

“…1.9–2.0 Å; Tables S3–S6, ESI†); as also observed in many POVs and chemically modified polyoxovanadates 3. The Sb–O bond lengths (1.9–2.0 Å) are typical for Sb III –O and match well those reported for other Sb-POVs 5,20. The cluster shells and {M(en) 3 } 2+ counterions in I–III are arranged in a layer-like fashion with alternating anions and cations along all three axes (Fig.…”

High Nuclearity Antimonato‐Polyoxovanadate Cluster {V15Sb6O42} as a Synthon for the Solvothermal in situ Generation of α‐ and β‐{V14Sb8O42} Isomers

“…Recently, we have studied the formation of different Sb‐POVs under hydrothermal conditions with in situ X‐ray diffraction experiments, demonstrating that distinct clusters can be obtained by adjusting the amine concentration. The results strongly suggest that the reduction of V V to V IV by the amine plays an important role for Sb‐POV formation thus explaining that for each synthesis of a new Sb‐POV the reaction conditions must be explored and adjusted by “trial‐and‐error”.…”

“…Recently,w eh ave studiedt he formationo fd ifferent Sb-POVs under hydrothermalc onditions with in situ X-ray diffraction experiments, [20] demonstrating that distinct clusters can be obtained by adjusting the amine concentration.T he results strongly suggestt hat the reduction of V V to V IV by the amine plays an importantr ole for Sb-POV formation thus explaining that for each synthesis of an ew Sb-POV the reaction conditions must be explored and adjusted by "trial-and-error".A way out of this unsatisfying situationw ould be the usage of ap re-formed Sb-POVclustera sastarting material, which can then be reacted with other educts for the generation of new compounds. Recently,w er eported the first water-soluble Sb-POV,n amely,{ Ni(en) 3 The highly unusual observation of the clustert ransformation encouraged us to explore this compound as as ynthon for the preparation of new Sb-POVs.…”

Nucleation and Crystal Growth of a {V14Sb8O42} Cluster from a {V15Sb6O42} Polyoxovanadate: In Situ XRD Studies

“…In contrast to polyoxomolybdates or polyoxotungstates, no suitable preformed high‐nuclearity clusters are available for the generation of Sb‐POVs, which can be regarded as an obstacle to the development of Sb‐POV chemistry. In a recent in situ energy‐dispersive X‐ray diffraction (EDXRD) study we investigated the formation of Sb‐POVs in the presence of 1‐(2‐aminoethyl)piperazine at the same ratio of Sb 2 O 3 /NH 4 VO 3 . The main result of this study was that all [V IV 18– n Sb 2 n O 42 ] 2 n – clusters with n = 2–4 can be obtained by varying the amine concentration, that is, the amine concentration and consequently the pH value controls the nuclearity of the cluster anion.…”