Novel Second Substituted Reaction of Oxo Clusters Reported

Jun 03, 2014     Email"> PrintText Size

Compared with lacunary oxo-tungsten clusters, the lacunary oxo-vanadium (V-O) clusters are very unstable and difficult to be isolated, resulting in that no available lacunary V-O clusters can be used as the precursors. Generally, their substitution reactions are in-situ realized. In V-O clusters, the Keggin-type V₁₈O₄₂ unit is common, which has eighteen V=O groups on the cluster cage. Some V=O groups on the V₁₈O₄₂ cage can be replaced in the forming process of clusters. For example, the As^III₂O units replace the V=O groups to form the first substitution products formularized as As_2nV_18-nO₄₂ (n = 2, 3, 4 …).  

Then, the similar Sb_2nV_18-nO₄₂ clusters were also obtained by replacing V=O groups with Sb^III₂O units. Moreover, the first substitution products with formula of Ge_2nV_18-nO_42+2n (n = 2, 3, 4 …) have been successfully made by the substitution of Ge₂O₃ units. The introduction of the substituted atoms with different attribute expands the research field of the oxo-cluster chemistry and introduces the new properties for the V-O clusters, as well as will further tune their structures and properties.  

Recently, Prof. YANG Guoyu’s group at Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, has made great progress on the second substitution reaction of the oxo clusters, and obtained two unprecedented V-O cluster open frameworks constructed from tetra-Cd^II-substituted Cd₄Ge₈V₁₀O₄₆ {Cd₄Ge₈V₁₀} cluster units and GeO₄ bridging groups under hydrothermal conditions, in which the {Cd₄Ge₈V₁₀} clusters are formed via the first substitution reaction of the main-group oxo metal groups (Ge₂O₃) and then the second substitution reaction of the late transition metal Cd(II) cations, respectively. 

It is the first 3-D vanadogermanates (VGOs) frameworks built by the largest number of TM-substituted {Cd₄Ge₈V₁₀} cluster shells linked by inorganic tetrahedral GeO₄ units and {V₄} clusters, of which the {Cd₄Ge₈V₁₀} cluster contains three different kinds metal cations. Notice that the second substitution products conforms the formula M_mGe_2nV_18-n-mO_42+2n-m (M = transition metal, n = 2, 3, 4 …; m = 2, 4…).  

The result has been published in J. Am. Chem. Soc. (2014, 136, 5065), which not only exploits novel second substitution reaction on the V₁₈O₄₂ cluster cage, but also establishes the basis of the functionality on the V₁₈O₄₂ cluster, owing to introducing the different metal cations. Therefore, it possesses important guidance significance for the synthesis and functionality of the novel substituted oxo clusters, which will open up a frontier field of polyoxometalate chemistry.  

Previously, Prof. YANG's group had also made a series of relevant progress on the V-O clusters. For instance, the Zn(II), Ni(II), and Cd(II) cations had been introduced into As_2nV_18-nO₄₂ cluster skeleton and replaced some V=O groups on cluster cages to build up the novel second substitution products with the formula: M_mAs_2nV_18-n-mO_42-m (n = 2, 3, 4… m = 1, 2 …), which have been published in Eur. J. Inorg. Chem. (2004, 2004) and Inorg. Chem. (2004, 43, 8005; 2005, 44, 2426; 2007, 46, 9503), respectively. Moreover, the second substitution reaction was successfully extended to the Ge_2nV_18-nO_42+2n system and made di-Cd^II-substituted VGO (Chem. Eur. J., 2010, 16, 13253). 

                

  

 The 3-D framework built by GeO₄ groups, {Cd₄Ge₈V₁₀} and {V₄} clusters, showing the ferrimagnetic property (Image by Prof. YANG's Group)